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Geology

Published by Field Museum of Natural History

New Series, No. 5

SYSTEMATICS OF THE SOUTH AMERICAN
MARSUPIAL FAMILY CAENOLESTIDAE

LARRY G. MARSHALL

September 19, 1980
Publication 1310

THE LIBRARY OF THE
OCT 141980

SYSTEMATICS OF THE SOUTH AMERICAN
MARSUPIAL FAMILY CAENOLESTIDAE

FIELDIANA
Geology

Published by Field Museum of Natural History

New Series, No. 5

SYSTEMATICS OF THE SOUTH AMERICAN
MARSUPIAL FAMILY CAENOLESTIDAE

LARRY G. MARSHALL

Assistant Curator of Fossil Mammals

Department of Geology

Field Museum of Natural History

September 19, 1980 Submitted for publication Oct. 16, 1979;

Publication 1310 accepted Dec. 21, 1979.

Library of Congress Catalog Card No.: 80-66381

US ISSN 0096-2651

PRINTED IN THE UNITED STATES OF AMERICA

CONTENTS

Abstract 1

Introduction 3

Scope of Study 4

Techniques of Study 5

Abbreviations 8

Acknowledgements 9

Historical Review 10

Relationships of Caenolestidae and Polydolopidae 15

Classification 16

Ecology 21

Behavior 22

Dental specializations and feeding habits 23

Systematics 28

Superfamily Caenolestoidea 28

Family Caenolestidae 30

Subfamily Caenolestinae 33

Tribe Caenolestini 34

Tribe Pichipilini 40

Subfamily Abderitinae 43

Tribe Parabderitini 43

Tribe Abderitini 47

Subfamily Palaeothentinae 51

Palaeothentinae — indeterminate 103

Palaeothentinae — unidentified 104

Summary of Evolution of Palaeothentinae 104

Phylogenetic Systematics 109

Methodology 109

Character analysis Ill

1) Antorbital vacuity Ill

2) Palatal vacuities Ill

3) Brain 112

4) Dental formula 112

5) Dental specializations 114

6) Teat number 115

7) Pouch or "marsupium" 115

8) Epipubic bones 116

9) Sperm pairing 116

10) Sperm morphology 117

1 1) Karyotype 118

12) Structure of pes 118

iii

Synopsis of the characters 120

Phylogenetic relationships of caenolestid subfamilies 126

Discussion and conclusions 132

References 1 36

LIST OF ILLUSTRATIONS

1 . Map of southern tip of South America showing vertebrate fossil localities ... 6

2. Proposed phylogeny of the Caenolestidae 7

3. Caenolestid indet. (Casamayoran) 32

4. Stilotherium dissimile Ameghino, 1887 (Santacrucian) 36

5. Stilotherium dissimile Ameghino, 1887 (Santacrucian) 37

6. Stilotherium dissimile Ameghino, 1887 (Santacrucian) 38

7. Phonocdromus gracilis Ameghino, 1894 (Santacrucian) 42

8. Parabderites minusculus Ameghino, 1902b (Deseadan) 44

9. Parabderites bicrispatus Ameghino, 1902c (Colhuehuapian) 45

10. Comparison of lower dentitions of various species of fossil Caenolestidae
showing relative size and proportions of teeth 48

11. Abderites meridionalis Ameghino, 1887 (Santacrucian) 50

12. Size distribution of various species of Palaeothentinae as indicated by length of
M,. 4 56

13. Size distribution of various species of Palaeothentinae as indicated by re-
lationship of length of P., and M, 57

14. Size distribution of various species of Palaeothentinae as indicated by re-
lationship of length and width of M, 58

15. Size distribution of various species of Palaeothentinae as indicated by re-
lationship of length of M, and M 2 59

16. Comparison of upper dentitions of various species of fossil Caenolestidae
showing relative size and proportions of teeth 60

17. Comparison of lower dentitions of various species of Palaeothentinae showing
relative size and proportions of teeth 61

18. Palaeothentes minutus Ameghino, 1887 (Santacrucian) 62

19. Palaeothentes minutus Ameghino, 1887 (Santacrucian) 63

20. Palaeothentes minutus Ameghino, 1887 (Santacrucian) 64

21. Palaeothentes primus Ameghino, 1902c (Colhuehuapian) 70

22. Palaeothentes intermedius Ameghino, 1887 (Santacrucian) 73

23. Palaeothentes intermedius Ameghino, 1887 (Santacrucian) 74

24. Palaeothentes lucina Ameghino, 1903 (Deseadan) 78

25. Palaeothentes lemoinei Ameghino, 1887 (Santacrucian) 80

26. Palaeothentes lemoinei Ameghino, 1887 (Santacrucian) 81

27. Palaeothentes boliviensis Patterson & Marshall, 1978 (Deseadan) 86

28. Palaeothentes chubutensis Ameghino, 1897 (Deseadan) 87

29. Palaeothentes aratae Ameghino, 1887 (Santacrucian) 88

30. Palaeothentes aratae Ameghino, 1887 (Santacrucian) 89

31. Palaeothentes praecursor Loomis, 1914 (Deseadan) 92

32. Acdestis oweni Ameghino, 1887 (Santacrucian) 94

33. Acdestis oweni Ameghino, 1887 (Santacrucian) 95

34. Acdestis oweni Ameghino, 1887 (Santacrucian) %

35. Dendrogram showing probable phylogenetic relationships of the genera and
species of Palaeothentinae 107

36. Cladogram showing probable relationships of suprageneric groupings of
Caenolestidae 130

LIST OF TABLES

1. Subdivision of the Caenolestoidea (ss) as conceived by different workers ... 12

2. Family-group names, type-genus of each nominal taxon, and type-species of
each nominal genus 16

3. Measurements of upper cheek teeth of Palaeothentes minutus 65

4. Measurements of lower cheek teeth of Palaeothentes minutus • 66

5. Statistics for some cheek teeth of Paleothentes minutus 67

6. Measurements of lower cheek teeth of Palaeothentes primus 71

7. Statistics for some lower cheek teeth of Palaeothentes primus 72

8. Measurements of cheek teeth of Palaeothentes intermedius 75

9. Statistics for some lower cheek teeth of Palaeothentes intermedius 76

10. Measurements of lower cheek teeth of Deseadan species of Palaeothentinae . 79

11. Measurements of upper cheek teeth of Palaeothentes lemoinei 82

12. Measurements of lower cheek teeth of Palaeothentes lemoinei 82

13. Statistics for some cheek tooth dimensions of Palaeothentes lemoinei 83

14. Measurements of cheek teeth of Palaeothentes aratae 90

15. Statistics for some lower cheek teeth of Palaeothentes aratae 91

16. Measurements of upper cheek teeth of Acdestis oweni 97

17. Measurements of lower cheek teeth of Acdestis oweni 98

18. Statistics for some cheek tooth dimensions of Acdestis oweni 99

19. Summary of some diagnostic characters of known species of Palaeothentinae 106

20. Summary of some diagnostic characters of the tribes and subfamilies of
Caenolestidae 121

ABSTRACT

The family CAENOLESTIDAE is, and according to the known fos-
sil record always has been, endemic to South America. Three sub-
families are recognized. The CAENOLESTINAE includes the most
generalized forms and is divisible into two tribes: the Caenolestini
(Casamayoran — Early Eocene through Recent) includes Caenolestes,
Lestoros, Pseudhalmarhiphus, Stilotherium, and Rhyncholestes; and
the Pichipilini new tribe (Colhuehuapian — Late Oligocene through
Montehermosan — Early Pliocene) includes Pliolestes, Phonocdromus,
and Pichipilus. The ABDERITINAE includes the most specialized of
known caenolestids and is also divisible into two tribes: the Parabderi-
tini new tribe (Deseadan — Early Oligocene through Santacrucian —
Early Miocene) includes Parabderites, and the Abderitini new rank
(Colhuehuapian through Santacrucian) includes Abderites and
Pitheculites. The subfamily PALAEOTHENTINAE (Deseadan
through Santacrucian) is structurally intermediate between the other
two subfamilies. A detailed systematic revision of the Palaeothentinae
is given, and two genera are recognized — Palaeothentes with eight
species (P. minutus, P. primus, P. intermedins, P. lucina, P. lemoinei,
P. boliviensis, P. chubutensis, P. aratae) and Acdestis with two
species {A. praecursor and A. oweni). These species are distinguished
largely on the basis of absolute size and on relative and absolute size
differences between P ;1 and M,.

Various aspects of ecology, behavior, dental specializations, and
feeding habits of living Caenolestinae are discussed. Based on study of
morphologically similar groups of living marsupials an attempt is made
to establish the feeding habits and dietary preferences of members of
the fossil subfamilies Palaeothentinae and Abderitinae.

The phylogenetic relationships of the caenolestid tribes and sub-
families are inferred using a cladistic analysis of shared derived
character states, and all groups are shown to be monophyletic. The
Caenolestini contains the most generalized forms with the highest
number of plesiomorphic states and serves as a basal stock for the

2 FIELDIANA: GEOLOGY

family. The Palaeothentinae and Abderitinae are sister groups, and
they and their common ancestors form the sister group of the
Caenolestinae.

It is concluded that caenolestids evolved from a didelphoid ancestor
in South America. This dichotomy occurred before Casamayoran time,
whereas subfamilial differentiation within the Caenolestidae was a
pre-Deseadan event. Caenolestids reached their known evolutionary
climax in the mid-Tertiary (i.e., Santacrucian time), when they were
represented by the three subfamilies, five tribes, seven genera, and 11
species. In beds of that age, caenolestids are the most abundant and the
most taxonomically diverse of the small Marsupialia. Although the
factors influencing the times of origin, adaptive radiation, decline in
diversity, and/or extinction of the various caenolestid groups are com-
plex, it is shown that most of these events can be correlated with the
appearance or disappearance of other mammalian groups.

INTRODUCTION

The Caenolestidae have been known to science since the latter part
of the last century. Living forms occur along the west coast of South
America from the Andes of Colombia and Venezuela in the north to
southern Chile in the south. Although three genera and seven nominal
species are known, these represent but relics of an impressive yet long
subdued Tertiary radiation. In this study, I attempt to synthesize
knowledge of the evolutionary history of the family Caenolestidae. I
include discussion of living forms but am concerned mostly with their
long-neglected fossil allies, the Abderitinae and especially the
Palaeothentinae.

SCOPE OF STUDY

This study is concerned primarily with the family Caenolestidae and
with the relationships of the included taxa. I have included considera-
tion of previous and present views on the relationships of Caenoles-
tidae with other marsupial groups to demonstrate that the included taxa
form a monophyletic unit relative to other marsupial families. I have
adopted the suprafamilial classification proposed by Clemens & Mar-
shall (1976) and place the family Caenolestidae in the Superfamily
Caenolestoidea, Order Marsupialia. This classification is not adopted
in opposition to the views of Ride (1964) and Kirsch (1968, 1977a) that
several orders be recognized within the Marsupialia. On the contrary, I
concur that the Marsupialia should indeed be divided into several ordi-
nal groups. However, most if not all of the orders recognized by those
workers are explicitly paraphyletic. The families of Marsupialia are in
need of a rigorous cladistic analysis to clarify their phylogenetic re-
lationships and to establish monophyletic groups. This study is a step
in that direction and is limited in scope to stabilizing nomenclature of
included taxa and to defining the taxonomic limits of the family
Caenolestidae.

This study includes a detailed systematic review of the caenolestid
subfamily Palaeothentinae. Information on the other caenolestid sub-
families is abbreviated, although of such a nature as to permit an
understanding of their interrelationships and of the relationships of
included taxa. A diagnosis for each subfamily is presented along with a
list of included taxa and synonymies. Because most of the taxa have
never been adequately diagnosed or characterized, I have included
some characters in the diagnosis the utility of which are yet to be
tested. This approach is the preferred alternative to omitting characters
that might have a diagnostic significance. Except for the Palaeothen-
tinae, only original references for generic and specific synonymies
within the other subfamilies are given, and no attempt has been made
to give a complete listing of literature citations.

During the course of this study, I was able to examine first hand all

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 5

pertinent known fossil materials, including type and referred speci-
mens. This work includes discussion and description of some new
material but is essentially based on a reappraisal of previously known
specimens and literature. All diagnoses of the family, subfamilies,
tribes, genera, and species have been revised. This study represents an
attempt to bring together in one place a modern, expanded, and syn-
thetic treatment of these animals, the relationships of which are now
better understood only in hindsight and through the pioneering efforts
of a multitude of earlier workers.

TECHNIQUES OF STUDY

The identity of the teeth and of the dental formula employed in this
study is based on the discussion on p. 112. In short, the basic marsupial
formula is taken to be IJ \ \ \ I, C{, P| f §, M| 1 || \\ the primitive
caenolestid formula is 1} \ \ 4, C{, P' \ ;', M} \ \ \\ and for Palaeothentinae
it is I{ | o» C}, P} i h MJ ; ;] t This conventional system for serial
designation of the antepremolar teeth is intended to be descriptive and
does not imply homology. However, homology is assumed for the
premolars and molars, at least among the Marsupialia.

I initiated my revision of the Palaeothentinae by ignoring all available
generic and specific names. I organized the specimens of Palaeothen-
tinae into groups which I regarded as warranting specific recognition.
These species I further organized into groups which I regarded as
warranting generic recognition. At that point, I ascertained the type
species and genera. Type specimens proved to be included in each
group, and for this reason it was not necessary to erect new names.

The Argentine fossil localities mentioned below (fig. 1) are shown on
maps and are discussed in greater detail in various papers as sum-
marized by Marshall et al. (In press). The chronology and usage of
South American Land Mammal Ages (fig. 2) follows Marshall et al. (In
press).

Specimens were measured to the nearest 0.1 mm. when possible,
using a pair of dial calipers. All measurements are in millimeters (mm.).

Fig. 1. Map of southern tip of South America showing vertebrate fossil localities
(circles) discussed in text.

Opposite:

Fig. 2. Proposed phylogeny of the Caenolestidae. The phylogeny of the Palaeothen-
tinae is based on this study and that of the Abderitinae and Caenolestinae are based on
Marshall (1976a and 1976b, respectively).

ABBREVIATIONS

The following abbreviations are used for specimens from in-
stitutional collections:

AC Amherst College, Amherst, Massachusetts

AMNH American Museum of Natural History, New York

BM(NH) British Museum (Natural History), London, England
DGM Divisao de Geologia e Mineralogia do Departamento Na-

cional da Producao Mineral, Rio de Janeiro, Brazil
FMNH Field Museum of Natural History, Chicago

KUVP University of Kansas, Department of Vertebrate

Paleontology
MACN Museo Argentino de Ciencias Naturales "Bernardino

Rivadavia," Buenos Aires, Argentina
MLP Museo de La Plata, La Plata, Argentina

MMP Museo Municipal de Ciencias Naturales de Mar del Plata

"Lorenzo Scaglia," Mar del Plata, Argentina
MNHN Museum National d'Histoire Naturelle, Paris, France

MNRJ Museu Nacional e Universidade Federal do Rio de

Janeiro, Rio de Janeiro, Brazil
NMNH National Museum of Natural History, Washington, D.C.

PU Princeton University, Princeton, New Jersey

Abbreviations used in the text, figure captions, and tables of mea-
surements are: C, canine; ca, approximate measurement; CV,
coefficient of variation; I, incisor; L, length; M, molar; N, number;
OR, observed range of sample; P, premolar; s, standard deviation of
sample; x, mean; W, width.

ACKNOWLEDGEMENTS

I am indebted to the following individuals for allowing me to study
specimens at their respective institutions — D. Baird (PU); J. Bonaparte
(MACN); M. Coombs (AC); P. Freeman (FMNH); L. Martin (KUVP);
R. Pascual (MLP); L. Price (DGM); C. Ray (NMNH); G. Scaglia
(MMP); F. L. de Souza Cunha (MNRJ); R. H. Tedford (AMNH); and
A. J. Sutcliffe [BM(NH)].

For many helpful comments on various phases of this study and/or
for reading the manuscript I thank J. A. W. Kirsch, M. C. McKenna,
R. Pascual, R. H. Pine, R. H. Tedford, W. D. Turnbull, and M. O.
Woodburne. The figures were drawn by Elizabeth Liebman from either
the original specimens or from epoxy casts.

Initial stages of this study were made possible by three grants (1329,
1698, 1943) from the National Geographic Society, Washington, D.C.,
and its completion was made possible by National Science Foundation
grant DEB-7901976.

HISTORICAL REVIEW

The first reference to a living caenolestid was made by Tomes (1860)
and was based on observation of a single juvenile specimen from
Ecuador. The specimen was not then given a generic or specific name
but was described as:
A small animal about the size of the Water shrew (Sorex fodiens), with external
characters and incisor teeth so much like those of the Soricidae as to have led in the
first instance to the belief that it was a placental Insectivore, perhaps in some degree
resembling the Solenodon of Cuba. However, the existence of a small and rudimen-
tary pouch sufficiently attests the implacental nature of the creature, which but for
this must certainly, as far as external appearances go be regarded as one of the
Soricidae.

Three years later Tomes (1863) named this animal Hyracodon
fuliginosus, although he made no further reference to its marsupial
affinity.

In 1887, Florentino Ameghino described and named a number of
fossil taxa, some of which are now regarded as caenolestoids. These
had been collected from the Santa Cruz Formation of Patagonia,
southern Argentina, by his brother Carlos the previous year. Floren-
tino immediately recognized the marsupial affinities of these taxa and
placed them in two families. Within the Plagiaulacidae he included
Abderites meridionalis, Acdestis Oweni, Palaeothentes Aratae,
Palaeothentes Lemoinei, Palaeothentes pachygnathus, Palaeothentes
intermedius, Palaeothentes pressiforatus, and Palaeothentes minutus;
and in Microbiotheriidae he included, along with two species of Mic-
robiotherium, Stilotherium dis simile.

In 1889, F. Ameghino included Stilotherium in a superfamily Mic-
robiotheria, family Microbiotheriidae, and in the superfamily
Plagiaulacoidea he included (among other groups) a family Abderitidae
with Abderites and a family Epanorthidae with Acdestis and Epanor-
thus.

In subsequent years, F. Ameghino named additional fossil taxa and
continued to acknowledge their marsupial affinity. In 1894, for exam-
ple, he recognized several families, all of which he placed in his sub-

10

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 1 1

order Paucituberculata. These included the Abderitidae with Abderites
and Mannodon; Decastidae with Decastis, Acdestis, Dipilus, Metrio-
dromus, Halmadromus, and Callomenus; Epanorthidae with Epanor-
thus, Metaepanorthus, Paraepanorthus, Prepanorthus, Halmaselus,
Essoprion, and Pichipilus; and Garzonidae with Garzonia, Phonoc-
dromus, Parhalmarhiphus, Halmarhiphus, Stilotherium, and Clado-
clinus.

In 1895, a second specimen of extant Recent caenolestid, this one
from Colombia, was sent to the British Museum. Thomas recognized
its affinities with Tomes' Hyracodon fuliginosus, but since the new
specimen was larger and different in appearance he gave it (1895a) a
different specific name, obscurus. He placed this species, along with
Tomes' fuliginosus, in a new genus, Caenolestes, because Hyracodon
was preoccupied by Hyracodon Leidy (1856, p. 91), a genus of fossil
Perissodactyla. Thomas (1895b) immediately recognized the affinities
of Caenolestes with members of Ameghino's fossil families Ab-
deritidae, Epanorthidae, Garzonidae, and Decastidae. Thomas (1895b,
p. 875) concluded:

. . . after a careful examination of the characters of the different fossil genera, I am
prepared to say that Caenolestes . . . falls into the Family, so that the name
Epanorthidae must be used for its recent as well as fossil members.

He accordingly classified Caenolestes in the Order Marsupialia, Sub-
order Diprotodonta, family Epanorthidae.
F. Ameghino (1897) later noted:

M. Thomas est venu a La Plata, rapportant avec lui un crane de Caenolestes que
nous avons soigneusement compare aux formes fossiles de Patagonie et nous avons
pu reconnaitre qu'il presente plus de rapports avec les Garzonidae qu'avec les
Epanorthidae. Pourtant il est probable que le Coenolestes [sic] devra constituer le
type d'une famille nouvelle.

Trouessart (1898, p. 1205), following Ameghino's (1897) suggestion,
proposed a new family Caenolestidae to include only Caenolestes.
Ameghino (1903) later included Zygolestes along with Caenolestes in
the Caenolestidae, and he placed this family, along with the Ab-
deritidae, Epanorthidae, and Garzonidae, in his suborder Paucituber-
culata (table 1).

Weber (1904) and Gregory (1910) recognized Caenolestes and its
fossil allies as a distinct suborder, Paucituberculata, of Marsupialia.
The other marsupials were included in the suborders Diprotodontia or
Polyprotodontia. Thus, these workers recognized a tripartite division
of Marsupialia.

Caenolestids are unique among marsupials in possessing, in combi-
nation, diprotodont modifications of their lower incisors, a polyproto-

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MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 13

dont upper incisor formula, and quadrate molars. In attempting to
establish caenolestid affinity, various workers have emphasized the
special importance of one of these features over the other. The princi-
ple questions include: (1) are caenolestids indeed as distinct from di-
protodonts and polyprotodonts as those groups are from each other, or
(2) are caenolestids related by structure of their lower incisors to Aus-
tralasian diprotodonts, or (3) by their upper incisor formula to poly-
protodonts?

Bensley (1903) concluded that the similarities between Caenolestes
and Australasian diprotodonts were the result of parallel or convergent
evolution, and that the diprotodont specializations evolved in-
dependently in the two groups.

Sinclair (1905, p. 81; 1906, p. 443) and Scott (1913) believed, as did
Ameghino and Thomas, that caenolestids were closely related
phylogenetically to Australasian diprotodonts. This relationship was
used as part of their evidence for existence of a former land connection
between South America and Australia. Sinclair was firm in this view,
but he did concede (1906, p. 443) that the striking similarities in dental
structure displayed by these groups "may be explained by con-
vergence."

Dederer (1909) and Broom (1911) emphasized the polyprotodont
affinities of Caenolestes and maintained that apart from the di-
protodont specializations of the lower incisors, it is a typical poly-
protodont in all its cranial characters. Gregory (1910, p. 211) also
maintained that the skull of Caenolestes shows no striking diprotodont
characters, and he regarded it and its allies as a distinct suborder — "an
offshoot of primitive polyprotodonts, which has paralleled the di-
protodonts of Australia in certain characters of the dentition/'

Based on an exhaustive monographic treatment of Caenolestes, Os-
good (1921) concluded that caenolestids lay phylogenetically between
the Australasian Peramelidae and Phalangeridae. The relationships
"are best expressed by classifying . . . [Caenolestes] in the suborder
Diprotodontia, family Palaeothentidae, subfamily Caenolestinae."

The issue of caenolestid affinity was in part clarified by Abbie's
(1937) study of the marsupial brain. He demonstrated that Australasian
Diprotodontia have ^fasciculus aberrans in the anterior commissure of
the brain, whereas Polyprotodontia lack this structure. Because
Caenolestidae lack this structure, they must be assigned to the Poly-
protodontia, but might still be regarded as ancestral to the Di-
protodontia.

Ride (1962, p. 299) reviewed data bearing on the identity and homol-

14 FIELDIANA: GEOLOGY

ogy of the diprotodont incisors in caenolestids and Australasian
phalangeroids. He concluded that the procumbent tooth in
phalangeroids is probably the I 3 (by homology with that of di-
delphoids), whereas in caenolestids it is the I, or I 2 . This fact sub-
stantiated the view that the dental similarities between Phalangeroidea
and Caenolestoidea are the result of convergence. Ride referred to the
procumbent specializations in the Phalangeroidea as diprotodonty
compared with pseudodiprotodonty in caenolestoids.

Further clarification of caenolestid affinity has resulted from study of
sperm. Biggers & DeLamater (1965) have demonstrated that pairing of
spermatozoa in the epididymes occurs in American didelphoids and
caenolestids tested, but not in Australasian forms. Sperm pairing is an
apomorphous condition among the Mammalia (see p. 1 16) and suggests
that all living American marsupials form a monophyletic group. These
workers further demonstrated that the morphology of the sperm in
Caenolestes is quite different from those of the other marsupials tested.
Pascual & Herrera (1973, 1975) have presented arguments support-
ing the view that caenolestids are more closely related to microbiothere
didelphoids than they are to any other known group. Winge (1923) had
earlier promoted this view and included Microbiotherium in a tribe
Microbiotheriini within the family Epanorthidae (see table 1).

Kirsch (e.g., 1971, in Hayman et al., 1971) compared sera of
Caenolestes obscurus and Lestoros inca with members of all the
families of living Marsupialia except the Thylacinidae. He (1977a, p.
92) concluded that the two caenolestids are more similar to each other
than they are to any other marsupial group. The tests further indicated
that:

. . . caenolestids have no greater similarity to any Australasian marsupial superfam-
ily examined than to the [American] didelphids; in fact, the data suggest that
caenolestids are less like any of the other superfamilies of marsupials than those
superfamilies are like each other. Thus serology does not seem to support a separa-
tion of living marsupials into Australasian and American stocks, but suggests that
the caenolestoids diverged from the principal line of marsupial evolution before the
separation of didelphoids and Australasian marsupials. Such a conclusion, however,
assumes that serological affinity strictly reflects propinquity of descent, and fur-
thermore, because only two closely similar, modern genera of caenolestoids were
studied, it leaves little allowance for variation within groups or for aberrant results
(Hayman et al., 1971, pp. 194-195).

RELATIONSHIPS OF CAENOLESTIDAE AND
POLYDOLOPIDAE

For many years it was conventional practice (e.g., Simpson, 1945) to
classify the families Caenolestidae and Polydolopidae in a superfamily
Caenolestoidea. This practice was based in part on the belief that the
sectorial or plagiaulacoid tooth was the first molar. Paula Couto (1952b)
clearly demonstrated, however, that in polydolopids the sectorial tooth
is the last premolar and not the first molar as is the case in those
caenolestids with plagiaulacoid dentitions.

Thus, evolution of sectorial teeth is a convergent (or parallel) feature
in these lineages. Because there was no convincing evidence to suggest
that polydolopids were any closer phylogenetically to caenolestids than
they are to didelphids, Clemens & Marshall (1976, p. 9) allocated the
Polydolopidae to a separate superfamily, the Polydolopoidea. This left
the Caenolestoidea an uncluttered and cohesive monophyletic group.

15

CLASSIFICATION

Six family-group names for caenolestoids have been proposed, and a
synopsis of their establishment and usage is given in Table 2.

Table 2. Family-group names, type-genus of each nominal taxon, and type-species of
each nominal genus (adopted from Marshall and Tedford, 1978, Table on p. 59).

Family-group
name

ABDERITIDAE
Ameghino, 1889, pp.
268, 269 [as Abderitesi-
dae (sic)]

EPANORTHIDAE
Ameghino, 1889, pp.
268, 270

GARZONIDAE
Ameghino, 1891b,
pp. 304, 307

DECASTIDAE
Ameghino, 1893b, p. 79

Name of type-genus of

nominal family-group

taxon

Abderites Ameghino, 1887,
p. 5.

Epanorthus Ameghino,
1889, p. 271 (replacement
name for Palaeothentes
Ameghino, 1887, p. 5)

Garzonia Ameghino, 1891b,
p. 307 (subjective junior
synonym of Stilotherium
Ameghino, 1887, p. 7)

Decastis Ameghino, 1891b,
p. 305 (subjective junior
synonym of Acdestis
Ameghino, 1887, p. 5)

CAENOLESTIDAE Caenolestes Thomas, 1895b,

Trouessart, 1898, p. 1205 p. 875 (replacement name

for Hyracodon Tomes, 1863
non Leidy, 1856)

PALAEOTHENTIDAE
(Sinclair, 1906, p. 417)
Osgood, 1921, pp. 143,
151

Palaeothentes Ameghino,
1887, p. 5

Name of type-species

of nominal type-genus,

and how fixed

Abderites meridionalis
Ameghino, 1887, p. 5, by
original designation

Palaeothentes aratae
Ameghino, 1887, p. 5,
through Palaeothentes
Ameghino, 1887, p. 5

Garzonia typica Ameghino,
1891b, p. 307, under
Article 68b

Decastis columnaris
Ameghino, 1891b, p. 305,
by original designation

Hyracodon fuliginosus
Tomes, 1863, through
Hyracodon Tomes, 1863, of
of which it is the type-
species by monotypy

Palaeothentes aratae
Ameghino, 1887, p. 5, by
subsequent designation by
Clemens & Marshall, 1976,

p. 72

16

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 17

ABDERITESIDAE was proposed by Ameghino (1889, pp. 268, 269)
to include Abderites Ameghino, 1887. The spelling Abderitesidae was
followed by Ameghino (1890, p. 174), although in later works he {e.g.,
1903, p. 159; 1906, p. 472) and all other workers used the spelling
Abderitidae. For Greek nouns ending in -tes, the stem for forming
family-group names is -/, alone (see Stoll et al., 1961, 1964, p. 133,
example 16). Following the Code [Art. ll(e)(ii) and Art. 29(a)], Ab-
deritesidae was an incorrect original spelling, and the change to Ab-
deritidae was a "justified emendation" [see Stoll et al., 1961, 1964, Art
33(a)(i)] and still dates from Ameghino, 1889. The incorrect spelling
Abderitesidae has not been used in any zoological literature for more
than 70 years. Sinclair (1906, p. 417) first recognized this group as a
subfamily (i.e., Abderitinae) of Caenolestidae Trouessart, 1898, p.
1205, and it has been regarded as such by all subsequent workers.
Abderitidae has remained unused as a valid family-group name for the
last 70 years.

EPANORTHIDAE was erected by Ameghino (1889, p. 272) to in-
clude Epanorthus and Acdestis. However, Epanorthidae Ameghino,
1889 is invalid because it is based on Epanorthus Ameghino, 1889, p.
271, an invalid replacement (see p. 54). Epanorthidae was last used as
a valid senior synonym by Scott (1937, p. 717).

GARZONIDAE was proposed by Ameghino (1891b, pp. 304, 307) to
include Garzonia and Halmarhiphus. Garzonia is now considered a
junior synonym of Stilotherium Ameghino, 1887, p. 7 (see Reig, 1955,
p. 62). Sinclair (1906, p. 417) included the Garzonidae within the
Caenolestinae, and the name has remained unused as a senior family-
group synonym for the last 70 years. The last use of Garzonidae as a
valid name was by Ameghino (1906, p. 417). Loomis (1914, p. 219) used
the names Garzoninae and Caenolestinae for the same group and thus
considered them synonymous. He included both in the family
Caenolestidae.

DECASTIDAE was proposed by Ameghino (1893b, p. 79) to include
Decastis, Acdestis and Dipilus. Decastis Ameghino, 1891b is rec-
ognized as a junior synonym of Acdestis Ameghino, 1887 (see p. 91).
Sinclair (1906, p. 417) included the Decastidae in the Palaeothentinae,
and the name has remained unused as a senior synonym for the last 70
years.

CAENOLESTIDAE was proposed by Trouessart (1898, p. 1205) for
Caenolestes only, and was first used as a subfamily by Sinclair (1906,
p. 416).

PALAEOTHENTINAE was proposed by Sinclair (1906, p. 417) to

18 FIELDIANA: GEOLOGY

include Palaeothentes, Callomenus, and Decastis. It was raised to the
rank of family by Osgood (1921, pp. 143, 151), but has remained unused
as a senior synonym since that time.

Trouessart (1898, pp. 1200, 1202, 1204, 1205; 1905, pp. 839, 840, 843,
844) recognized four families within Thomas' (1895b) group
Asyndactylia — the Abderitidae, Epanorthidae, Garzonidae, and
Caenolestidae; Ameghino (1903, p. 159) recognized four families within
his group Paucituberculata — the Abderitidae, Epanorthidae,
Coenolestidae [sic], and Garzonidae; and Palmer (1904, pp. 876, 881,
882) recognized three families — the Abderitidae, Epanorthidae (which
included Caenolestidae and Decastidae), and Garzonidae. Sinclair
(1906, p. 416) recommended grouping ". . .all the Santa Cruz di-
protodont marsupials in a single family, which may be called the
Caenolestidae (Trouessart, 1898, p. 1205) from its only surviving and
best known representative Caenolestes." Within this family, Sinclair
recognized three subfamilies — the Caenolestinae (with Caenolestes,
Halmarhiphus, Garzonia), the Palaeothentinae (with Palaeothentes,
Callomenus, Decastis), and the Abderitinae (with Abderites).

Sinclair's classification has been the one most commonly used for
the last 70 years. However, no ratification has been given by sub-
sequent workers that any of these supergeneric names are valid under
the present code, and some certainly are not. They are, however, the
names used almost universally in recent literature and are the most
readily understood by any present student of marsupials or mammals in
general (Simpson, 1970, p. 57n). Pertinent publications using this
classification include Clemens & Marshall (1976, p. 10), Marshall
(1976a, p. 83), Pascual & Herrera (1973, p. 44), Piveteau (1961, p. 619),
Simpson (1930, p. 9; 1945, p. 44; 1970, p. 58), Zittel (1925, p. 27).

The following deviations from this usage are worthy of note.
Thomas' (1895b, p. 875) practice of placing Caenolestes in the
Epanorthidae was followed by Osborn (1910, p. 517). Osborn also re-
cognized a superfamily Caenolestoidea, but no family Caenolestidae.
Osgood (1921, p. 151) placed Caenolestes in the subfamily Caenoles-
tinae, family Palaeothentidae. Winge (1923, p. 84) recognized one fam-
ily, Epanorthidae, and included within it (among other groups) the
Caenolestini (with Halmatorhiphus [sic], Caenolestes, Garzonia) and
Epanorthini (with Epanorthus, Callomenus, Decastis, Abderites)
(table 1). Scott (1937, pp. 717, 722) recognized one family, Epanor-
thidae, with three subfamilies — Caenolestinae, Epanorthinae, and Ab-
deritinae.

If the Law of Priority is strictly applied, the names Caenolestidae

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 19

and Caenolestinae of the classification most commonly used for the last
70 years would have to be replaced by Abderitidae and Garzoninae.
This usage would upset continuity and stability in nomenclature of this
diverse and important group of South American mammals.

In view of this, Marshall & Tedford (1978, p. 58) submitted an appli-
cation to the Commission to safeguard the family-group names
Caenolestidae Trouessart, 1898, and Palaeothentidae (Sinclair, 1906)
Osgood, 1921 , from the threat to their stability represented by the prior
names Abderitidae Ameghino, 1889, Epanorthidae Ameghino, 1889,
Garzonidae Ameghino, 1891b, and Decastidae Ameghino, 1893b. They
asked the Commission:

(1) to use its plenary powers to rule that the family-group names
Abderitidae Ameghino, 1889, Garzonidae Ameghino, 1891b, and
Decastidae Ameghino, 1893b, not be given nomenclatural pre-
cedence over the family-group names Caenolestidae Trouessart,
1898, and Palaeothentinae Sinclair, 1906;

(2) to place the following family-group names on the Official List of
Family-Group Names in Zoology with the endorsements that:

(a) Caenolestidae Trouessart, 1898, be given nomenclatural
precedence over Abderitidae Ameghino, 1889, Gar-
zonidae Ameghino, 1891b, and Decastidae Ameghino,
1893b;

(b) Palaeothentinae Sinclair, 1906, be given nomenclatural
precedence over Abderitidae Ameghino, 1889, Gar-
zonidae Ameghino, 1891b, and Decastidae Ameghino,
1893b;

(c) Abderitinae Ameghino, 1889, not be given
nomenclatural precedence over Caenolestidae Troues-
sart, 1898, or Palaeothentinae Sinclair, 1906;

(d) Garzonidae Ameghino, 1891b, not be given
nomenclatural precedence over Caenolestidae Troues-
sart, 1898, or Palaeothentinae Sinclair, 1906;

(e) Decastidae Ameghino, 1893b, not be given
nomenclatural precedence over Caenolestidae Troues-
sart, 1898, or Palaeothentinae Sinclair, 1906;

(3) to place the following generic names on the Official List of
Generic Names in Zoology:

(a) Caenolestes Thomas, 1895a (gender, masculine);

(b) Palaeothentes Ameghino, 1887 (gender, masculine);

(c) Abderites Ameghino, 1887 (gender masculine);

20 FIELDIANA: GEOLOGY

(d) Garzonia Ameghino, 1891b (gender, feminine);

(e) Decastis Ameghino, 1891b (gender, feminine);

(4) to place the following specific names on the Official List of
Specific Names in Zoology:

(a) fuliginosus Tomes, 1863, as published in the binomen
Hyracodon fuliginosus (name of type-species of
Caenolestes Thomas, 1895a);

(b) aratae Ameghino, 1887, as published in the binomen
Palaeothentes aratae (name of type-species of
Palaeothentes Ameghino, 1887);

(c) meridionalis Ameghino 1887, as published in the bino-
men Abderites meridionalis (name of type-species of
Abderites Ameghino, 1887);

(d) typica Ameghino, 1891b, as published in the binomen
Garzonia typica (name of type-species of Garzonia
Ameghino, 1891b);

(e) columnaris Ameghino, 1891b, as published in the bino-
men Decastis columnaris (name of type-species of De-
castis Ameghino, 1891b).

In this study I adopt Sinclair's (1906) classification on the assumption
that the Commission will use its plenary powers to endorse the recom-
mendation of nomenclatural usage as requested by Marshall & Tedford
(1978). This classification is used because it is the preferred one based
on a careful consideration of the phylogenetic relationships of
caenolestid genera and of their suprageneric groupings. The only addi-
tion to Sinclair's classification is in formal recognition of two tribes
each of Caenolestinae and Abderitinae. This is based on my (1976b and
1976a, respectively) documentation of two major groupings within each
of these subfamilies.

ECOLOGY

Living caenolestines prefer densely vegetated, cold, and wet forest
habitats, ranging from sea level to elevations exceeding 14,000 ft. They
prefer moist, often moss-covered slopes and ledges, well protected
from cold winds, mist, and rain. In the high cold paramos of Colombia,
Ecuador, and Peru they are typically found in the scrub adjacent to
meadows (Osgood, 1921, p. 17; Collins, 1973, p. 169; Kirsch & Waller,
1979, p. 390).

21

BEHAVIOR

Caenolestines are terrestrial and crepuscular or nocturnal in habits.
Young ones are agile climbers (Kirsch & Waller, 1979, p. 393), and the
tail is used for this purpose. However, in no caenolestine is the tail
truly prehensile, either in a ventral or in a dorsal direction. Kirsch &
Waller (1979, p. 394) report that:

... an animal held dangling by the tip of the tail can swing itself ventrally, grasp the
tail with the forepaws, and climb up "hand over hand" ....
A tripedal stance — that is on the hind legs and tail — appears to be as common as a
quadrupedal one in resting caenolestids. Often after a period of activity, which could
be quite sustained (45 minutes for C. obscurus in the case of one session . . .),
caenolestids would suddenly cease movement, close their eyes at least part way and
drop the tip of the snout to the substrate. After a few minutes in this posture they
seemed to revive and resumed activity. Another resting posture consisted of tucking
the head between the forelegs while setting on the hindquarters. Once an animal (C
obscurus) was observed sitting on its hindlegs with its tail passed between them,
much like a kangaroo. However, this posture was certainly not usual, nor were
caenolestids ever observed to sleep or rest on their side . . . (Kirsch & Waller, 1979,
p. 394).

Using a high-speed motion picture camera, Kirsch & Waller (1979, p.
394, fig. 1) photographed species of Caenolestes and Lestoros. The
locomotion of these animals was observed to be typically symmetrical.
At higher speeds they assumed a full bound, using the fore- and hind-
legs nearly or exactly together. In all of the gaits observed by Kirsch &
Waller the tail was used:

... as a balancing device on sloping or uneven surface, when it may be rotated
violently to maintain the animal's equilibrium; on level ground it is usually held
rigidly and curving slightly downward.

These workers did not observe any caenolestid adopt a saltorial pro-
gression as Gregory (1922) suggested that they might do.

22

DENTAL SPECIALIZATIONS AND FEEDING HABITS

There is a marked regional differentiation of dentition in caenoles-
tids. This reflects differences in function between the anterior and the
posterior teeth. The lower dentition is characterized by an enlarged
procumbent medial incisor (the I,) and a reduced often rudimentary
dentition between it and the P., or M, (fig. 6). This regional differentia-
tion is influenced largely by selection for optimal designs for first ac-
quiring, then breaking down food. The initial stages of feeding involve
acquiring (ingesting) a bit of food and cutting it into manageable pieces
before mastication. This usually involves the incisors, canines, and/or
premolars. Food is then chewed (masticated) before swallowing, and
this is accomplished primarily by the molar teeth. The differences in
dental morphology can often be related to the physical properties of the
foods (Kay & Hylander, 1978, p. 173).

Bensley (1903) suggested that diprotodonty may have originated as
an adaptation for grasping and piercing small prey, probably insects.
This view was reinforced by Osgood's (1921) report of mainly insect
and arachnid remains in the stomachs of three specimens of
Caenolestes obscurus.

Based on observation and study of living caenolestids killing prey,
Kirsch (1977b) demonstrated that the original adaptive value of di-
protodonty may be related to piercing and killing rather than grasping.
Kirsch (1977b, p. 287) kept live specimens of Caenolestes obscurus
from Colombia and fed them live newborn rats:

. . . [C. obscurus] did not use its incisors simply to grasp the rat, but made stabbing
motions with the lower jaw. This rapier-like motion of the procumbent incisors was
followed by manually shifting the young rat to the side of the mouth for actual
ingestion and mastication by the cheek teeth; the incisors were never used to bite off
pieces of the rat. Devouring the prey progressed in the normal marsupial manner, by
first biting the head off and then proceeding posteriorly.

Drawings of this sequence traced from a film of a kill are shown by

Kirsch (1977b, fig. 14).
These films demonstrate that Caenolestes is certainly competent to deal with verte-
brate prey and suggest that the primary use of the diprotodont teeth is in killing. C.
obscurus may well be an important small predator in its native habitat, for in south-

23

24 FIELDIANA: GEOLOGY

ern Colombia it occurs sympatrically with several species of cricetid rodents. I
would suggest . . . [that diprotodonty] ... is an effective adaptation for killing
relatively large and vigorous prey (Kirsch, 1977b, p. 287).

Caenolestids would ordinarily pick up and hold small pieces [of meat] in the
forepaws, but would tug on larger lumps with their incisors in order to pull off
smaller bits. As this operation usually failed, they would chew off pieces with the
cheek teeth; this as well as subsequent mastication was accompanied by a distinct
clicking sound. As the labial cusps of caenolestid upper molars are much higher than
the lingual, and the upper and lower molars form shearing surfaces in occlusion
. . . , the clicking sounds probably are produced during shearing (Kirsch & Waller,
1979, p. 392).

Worms given to C. convelatus were held in the forepaws while the animal sat on its
hindlegs and tail and fed the worms directly into the side of the mouth, making only
occasional perfunctory nips with the incisors (Kirsch & Waller, 1979, p. 392).
Much speculation has been aroused by the peculiar lip flaps of caenolestids (Greg-
ory, 1922; Lonnberg, 1921; Osgood, 1921), the various suggestions being that they
hold, convey inwards, or eject food items. Our observations suggest that these
structures help prevent the sensory vibrissae and fur at the side of the mouth from
becoming clogged with blood and dirt, as might result from the caenolestids' method
of feeding, and also prevent dirt from entering the mouth (Kirsch & Waller, 1979, p.
393).

Following a meal of rats, C. obscurus would rub its muzzle on the cage floor to
remove some of the blood and wash off the rest by licking its forepaws and rubbing
them over the snout. Other species of Caenolestidae also used the forepaws, either
together or separately, in washing. Additionally, caenolestids use the tongue to wash
the body fur and the hind feet to scratch. They frequently sit on the hind legs and tail
during grooming and other operations (Kirsch & Waller, 1979, p. 393).

In Abderitinae the lower dentition is further characterized by a
hypertrophied trenchant P :{ and/or M, (fig. 10). This type of dentition in
which one or more of the lower cheek teeth is/are modified into large,
simple, laterally compressed blades with serrated cutting eges has been
termed Plagiaulax-typus or plagiaulac older Typus by Abel (1931, pp.
326-328). This name was given in allusion to its occurrence in members
of the multituberculate suborder Plagiaulacoidea. A plagiaulac old type
of dentition has evolved independently in a number of mammalian
orders — twice in early Tertiary Primates (Carpolestidae and
Saxonella — see Rose, 1975, p. 51), once in ptilodontoid multitubercu-
lates (see Simpson, 1933), and at least three times in marsupials (once
each in Australian phalangeroids, in South American polydolopoids,
and in caenolestoids — see Paula Couto, 1952b).

These blade-like specializations may involve more than one tooth as
in multituberculates, which incorporate P 2 - 4 or P 3 . 4 , and in the
caenolestoid Parabderites, which used P ;i -M, (figs. 8, 9). More typi-
cally, these specializations are restricted to a single lower tooth, such
as the P 4 in carpolestids, the P,$ in Saxonella, the P 3 in phalangeroid and

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 25

polydolopoid marsupials, and the M, in Abderitini. Rose (1975, p. 51)
has noted that the adaptive significance of the plagiaulacoid dentition
may be basically similar in the varied types possessing it, but dissimilar
upper dentitions in most of these mammals suggest that the function is
variable. Eisenberg (1978) further cautioned that evaluation of dietary
inferences should not be based solely on study of a single system such
as tooth structure, but should be cross checked against other systems,
such as morphology of the gut (e.g., Vorontsov, 1962). Since this is not
possible with fossil species, unequivocal interpretations of their feed-
ing behavior may be impossible (Kay & Hylander, 1978, p. 174).

Based on his review of plagiaulacoid groups and of consideration of
the feeding habits and food types of living plagiaulacoid forms,
Simpson (1933) considered plagiaulacoidy an adaptation for herbivory,
being especially efficient for dealing with coarse vegetation. Rose
(1975, p. 62) has suggested that the plagiaulacoid tooth (in carpolestids
at least) was used primarily during the puncture-crushing stage of mas-
tication. He further suggested that the primary diet of these forms
consisted of coarse herbage, fruits, and seeds. Most recently, Kay &
Hylander (1978) have presented a competent and detailed analysis of
the dentition and feeding adaptations of living phalangeroid marsupials.
They conclude (p. 187) that a large plagiaulacoid tooth reflects in-
creased ingestion and mastication of fibrous foods in this region. This
includes hard-shelled insects, coarse leaves, stems, seeds, etc.

The best indication of the use and function of the plagiaulacoid den-
tition of the Abderitini comes from the study by Dimpel & Calaby
(1972) of the feeding behavior, habits, and preferred food items of the
living Australian "Mountain pigmy possum," Burramys parvus. This
animal is similar in size to abderitines (especially to Pitheculites), and,
except for the fact that the plagiaulacoid tooth in Burramys is the P t!
and in Abderitini it is the M,, the dentitions are almost identical (see
Simpson, 1933, fig. 1C, Abderites; IE, Burramys).

Dimpel & Calaby (1972, pp. 103-104) noted:

. . . the faeces of our first three specimens [of Burramys parvus] taken from the
traps before the animals had fed, consisted largely of plant material, with some
insect remains. With subsequent animals the faeces have contained mostly in-
vertebrate remains, including worms, beetles, grasshoppers, and spiders. In captiv-
ity Burramys have been fed a variety of fruits and seeds such as sliced apple and
pear, grapes, soaked raisins, walnut chips, raw peanuts, sunflower seeds, honey,
and insects, such as meal-worm larvae and moths. All of these are readily eaten.
Feeding trials in the first couple of weeks of captivity indicated that a greater amount
of fruit and seeds was eaten than insect material. ... It is probable that in the wild,
Burramys feed on whatever palatable fruits, seeds, or invertebrates are available.

26 FIELDIANA: GEOLOGY

Food is picked up with the incisors then transferred to and manipulated with the
forepaws while the animal squats on its hind-quarters. The food may be held in one
or both forepaws. The soft flesh of fruits is bitten off with the incisors and chewed
with the molars. The skins are not eaten and Burramys have been observed holding
pieces of apple and grape and removing the last fragment of flesh by pulling the skin
with their forepaws against the lower incisors. Soft bodied insects such as moths are
usually dealt with by the incisors. With insects having a hard cuticle such as meal-
worm larvae the animal may begin biting with the incisors but usually the insect is
held in the forepaws at the side of the mouth and chopped up with the sectorial
premolars. Hard-shelled seeds such as sunflowers are invariably held at the side of
the mouth and bitten with the premolars. Usually the seed case is opened with a
single bite. Peanuts are mostly nibbled with the incisors but the premolars are used
also to break up fragments.

. . . Burramys stores food in its nests. Only nuts and seeds are stored in these
caches. Invertebrates are eaten when caught and if excess insects are provided they
are never taken to the nests and stored. The nuts and seeds are held in front of the
premolars, resting on the lower incisors. Animals may carry peanuts or sunflower
seeds for as long as 15 minutes, and indulge in other activities such as scratching
themselves or exploring their cages, before taking the food to their nests.

The dental specializations of Palaeothentinae are intermediate in
virtually all respects between those of the more generalized Caenoles-
tinae and the more specialized Abderitinae. Specializations seen in the
Palaeothentinae compared with the Caenolestinae include relative en-
largement in size of the protoconid-paraconid crest and of absolute size
of M,, and the increase in size of the P 3 (figs. 11, 16, 17). Shear occurs
between the labial side of the M, trigonid and the posterolingual surface
of the P 3 . These shear specializations are accentuated in evolution of
Palaeothentes by incorporation of the P 3 as a sectorial element,
whereas in Acdestis, the P 3 is reduced in size and lacks a sectorial
function.

Among the living Australasian phalangeroid marsupials, analogous
dentitions to those of Palaeothentinae are found in Petaurus. This ani-
mal has an exceptionally small P, ? and is primarily gumivorous. The
dentition of Petaurus is also similar to that of Dactylopsila which eats
high proportions of soft plant foods and insect grubs (Kay & Hy lander,
1978, p. 186).

Based on this analogy, the primary food items of Palaeothentinae
probably included both leaves and soft-bodied insects. The feeding
habits of this group thus appear to have been intermediate between the
more carnivorous Caenolestinae and the apparently more herbivorous
Abderitinae. Species of Palaeothentes were probably able to cope with
slightly coarser items due to the relatively large, but unserrated P 3 ,
whereas species of Acdestis were confined by their relatively small P 3
to softer and more succulent items.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 27

In Palaeothentinae and Abderitinae, the diprotodont incisors may
have played a major role in incisal gnawing during food acquisition as is
reported for living phalangeroids (Kay & Hylander, 1978, p. 186).

SYSTEMATICS

Order MARSUPIALIA Illiger, 1811, p. 75

Superfamily CAENOLESTOIDEA (Trouessart, 1898, p. 1205)

Osborn, 1910, p. 517 (=Paucituberculata Ameghino, 1894, p. 332;

Asyndactylia Thomas, 1895b, p. 870)

The diagnoses given by Ameghino (1898) for his order Paucituber-
culata and its included taxa are:

PAUCITUBERCULATA Ameghino. — Las muelas persistentes son cuadrangu-
lares, con cuatro o cinco tuberculos principales y la septima muela inferior siempre
presente. Son numerosisimos en las formaciones eocenas y cretaceas de Sud
America y tiene tambien algunos representes en el Laramico de Norte America
{Cimolestes Marsh, Telacodon Marsh y Batodon Marsh). Se ha encontrado re-
cientemente un genero vivo que habita Nueva Granada y Ecuador: el Coenolestes
Thomas, con dos especies de talla muy reducida y aliado de los Garzonidae del
Eoceno. Todos los representantes de este suborden son muy pequenos, compara-
bles por el tamano a lauchas y ratones. Las especies fosiles argentinas se distribuyen
en tres familias: Abderitidae , Epanorthidae y Garzonidae .

ABDERITIDAE. Se distinguen por la cuarta muela inferior muy grande, cortante
y rayada verticalmente; muelas anteriores de corona baja y aplastada como en
Stagodon. Un solo genero conocido: Abderites Ameghino, con varias especies:
Abderites meridionalis, crassiramis, altiramis, serratus, tenuissimus Ameghino,
todas del pi so Santacruceno.

EPANORTHIDAE. Con la cuarta muela inferior un poco mas grande que la
quinta y cortante, pero no rayada verticalmente. * Todas las especies, a excepcion de
una sola: el Epanorthus chubutensis, son del piso Santacruceno. Decastis
Ameghino, tercera muela inferior rudimentaria y con sola raiz en forma de columna:
Decastis columnaris y rurigenus Ameghino. Parecido al anterior es Acdestis
Ameghino, con la tercera muela inferior igualmente pequena, pero con dos raices;
tres especies: Acdestis Oweni, parvus y elatus Ameghino. El genero Dipilus
Ameghino presenta la tercera muela inferior rudimentaria, la cuarta sumamente
grande y cortante y la septima atrofiada: Dipilus Spegazzinii y Bergi Ameghino. El
genero Metriodromus Ameghino presenta entre el incisivo hipertrofiado y la cuarta
muela, solo cuatro dientes stagodoniformes, en vez de cinco: Metriodromus cras-
sus, spectans y crassidens Ameghino. Halmadromus vagus Ameghino, con solo tres
dientes inferiores stagodoniformes. Callomenus Ameghino, parecido al anterior,
pero con la cuarta muela inferior birradiculada: Callomenus intervalatus, ligatus y
robustus Ameghino. El genero Epanorthus Ameghino, que sirve de tipo a la familia,
tiene la cuarta muela inferior bien desarrollada, con dos raices separadas y corona

28

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 29

conicocomprimida, sin tuberculos accesorios; los dientes stagodoniformes son en
niimero de cuatro; comprende numerosas especies: Epanorthus chubutensis
Ameghino, del Cretaceo de Patagonia, que es la sola especie de esta familia que no
procede del piso Santacruceno; Epanorthus Aratae, ambiguus, Lemoinei, pachyg-
nathus, pressiforatus, simplex, lepidus, inaequalis Ameghino. Metaepanorthus
Ameghino, parecido al anterior, pero con la cuarta muela inferior provista de un
tuberculo accesario anterior y otro posterior: Metaepanorthus intermedius, com-
plicatus, Holmbergi Ameghino. Paraepanorthus minutus Ameghino, presenta la
cuarta muela inferior con un solo tuberculo accesorio adelante, es de tamano muy
pequeho y debio ser sumamente abundante, pues es el plagiaulacoidio que ha dejado
mas restos Prepanorthus lanius Ameghino, canino y primera a cuarta muelas
superiores, inclusive, separadas una de otra y muy comprimidas en forma de hojas
cortantes. Halmaselus valens Ameghino, con la tercera muela con dos raices, como
la cuarta. Essoprion Ameghino, primera muela inferior ausente y la cuarta bien
desarrollada y con dos raices distintas, dos especies: Essoprion coruscus y con-
sumptus Ameghino. Pichipilus Ameghino, corona de las muelas inferiores con un
pliegue profundo al lado interno que les da una forma semilunar o en arco de circulo,
dos especies: Pichipilus Osborni y exilis Ameghino, ambas sumamente pequenas.

*En la formacion Patagonica del rio Deseado y del lago Musters se han encontrado
restos de les especies indeterminadas de los generos Abderites y Epanorthus. — (Del
((Suplemento: Adiciones y Correcciones)), pagina 7.)

GARZONIDAE. Segunda y tercera muela inferiores siempre birradiculadas; la
cuarta inferior apenas un poco mayor que la quinta; cuarta a sexta inferiores
bilobadas sobre el lado externo, con dos tuberculos externos y tres o cuatro sobre el
lado interno; estas muelas presentan un gran parecido con las de los Didelphys.
Todos los representantes conocidos de este grupo son excesivamente pequenos y
hasta ahora exclusivos del piso Santacruceno. Garzonia Ameghino, segundo y ter-
cera muelas inferiores birradiculadas, cuarta a sexta con dos tuberculos externos y
tres internos y ademas un tuberculo rudimentario sobre el lado posterior, ultima
inferior conica y de una sola rafz, tres especies: Garzonia typica, captiva y minima
Ameghino. El genero Phonocdromus se distingue por las muelas inferiores cuarta a
sexta con dos tuberculos externos y cuatro internos, ambas filas son separadas por
un surco longitudinal, dos especies: Phonocdromus patagonicus y gracilis
Ameghino, Parhalmarhiphus annectens Ameghino, muelas inferiores cuarta a sexta
cuadrangulares, con cuatro tuberculos principales dispuestos por pares, dos
adelante y dos atras; ultima inferior conicocolumnar. Halmarhiphus Ameghino,
cuarta a sexta muelas inferiores con dos ciispides externas y tres internas, la anterior
externa mucho mas elevada que las otras, ultima muela inferior con dos raices bien
separadas, dos especies: Halmarhiphus nanus y didelphoides Ameghino.*

*Agreguese en el genero Halmarhiphus: Halmarhiphus guaraniticus, n. sp.,
muelas inferiores con el tuberculo anterior externo de igual altura que el posterior
externo y con un fuerte cigulo basal. Longitud del espacio ocupado por las cuarta y
quinta muelas: 3.5 milimetros. Formacion Guaranitica. — (Del ((Suplemento:
Adiciones y Correcciones)), pagina 7.)

El genero Stilotherium Ameghino tiene once dientes en cada lado de la mandfbula
inferior, el gran incisivo hipertrofiado, cuatro dientes unirradiculados
stagodoniformes sumamente pequenos, dos dientes birradiculados de corona simple
y cuatro muelas de corona complicada, cada muela con cuatro tuberculos dispuestos
por pares, uno anterior y otro posterior, y un tuberculo impar anterior sobre el lado
interno, unido al anterior externo por una cresta en arco de circulo, dos especies:

30 FIELDIANA: GEOLOGY

Stilotherium dissimile Ameghino, de tamano diminuto y Stilotherium grande
Ameghino, de tamano cuatro veces mayor. Cladoclinus Copei Ameghino, carac-
terizado por la rama ascendente inclinada hacia atras, formando una prolongation
casi horizontal del borde alveolar.*

* A continuation del genero Cladoclinus cdloquese el Zygolestes paranensis men-
cionado en la pagina 243; ademas Zygolestes entrerrianus n. sp., de talla doble que la
del precedente. Longitud de la cuarta muela inferior: 3.5 milfmetros. Formation
Entrerriana. — (Ibidem: pagina 7). (Ver. pagina 714 de este tomo).

The family Caenolestidae and the subfamilies Caenolestinae,
Palaeothentinae, and Abderitinae were diagnosed by Sinclair (1906, pp.
416-417) as follows:

Family: CAENOLESTIDAE. — Pes, so far as known (Caenolestes), non-
syndactylous. Sectorials, when present, restricted to the posterior premolar above
and the first molar below. Superior premolars three in number (Palaeothentes,
Caenolestes), the anterior and median small, the posterior large and trenchant.
Functional lower premolars 2-none. Vestigial teeth always present in the lower
jaw. Molars rooted, brachyodont, tuberculo-sectorial or buno-lophodont, under-
going progressive complication in the superior series by the addition of a
hypocone. Hypertrophied lower incisors lanceolate with cutting edges enamel
layer confined to the outer face.

First Subfamily: CAENOLESTINAE.— Dental formula ] A d. 2 , \ {Caenolestes). Sec-
torials not developed. First and second superior molars fully quadritubercular,
third and fourth tritubercular (Caenolestes). Lower molars tuberculo-sectorial,
approaching lophodont when worn. Median and posterior lower premolars
double-rooted and functional. Genera: Caenolestes, Halmarhiphus, Gar-
zonia.

Second Subfamily: PALAEOTHENTINAE.— Dental formula \-& u J. Posterior
superior premolar and first lower molar sectorial in function. Sectorials unstriated.
First upper molar fully quadritubercular, second with rudimentary hypocone,
third and fourth tritubercular (Palaeothentes). Lower molars lophodont. M, with
prominent metaconid. Posterior lower premolar double-rooted and functional or
single-rooted and reduced. Genera: Palaeothentes, Callomenus, Decastis.

Third Subfamily: ABDERITINAE.— Dental formula j; ? 4 ; ( , I. First lower molar with
protoconoid-paraconoid blade developed into a striated sectorial shear with ser-
rate margin, greatly elevated above the general level of the tooth row. Metaconoid
absent on M,. Second, third and fourth lower molars bunolophodont. Functional
lower premolars wanting in known Santa Cruz forms, the posterior tooth being
single-rooted and vestigial. Genus: Abderites.

Revised diagnoses for the family Caenolestidae and the subfamilies
and tribes follow.

Family CAENOLESTIDAE Trouessart, 1898, p. 1205

(Including Epanorthidae Ameghino, 1889, pp. 268, 270;

Abderitesidae [sic] Ameghino, 1889, pp. 268, 269;

Garzonidae Ameghino, 1891b, pp. 304, 307;

Decastidae Ameghino, 1893b, p. 79;
Palaeothentidae Osgood, 1921, pp. 143, 151)

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 31

Diagnosis. — Small size; I|:1, C}, P 2 3 { , M:}; mandibular rami unfused
along symphysis; angular process of dentary is prominent and is
strongly inflected; one large laterally compressed procumbent gliriform
incisor in each lower jaw with enamel along only outer surface, fol-
lowed by six to seven tiny, spaced vestigial teeth; MJ::{, with sharp
reduction in size from M} to Mj, M:} reduced but not vestigial;
hypocone present on M 1 " 3 (large on M 1 , very small on M 3 ); M, modified
into sectorial "plagiaulacoid" blade in some groups; "intermediate
conule" at inner base of metacone present in early and generalized
forms; pes didactylous; palatal vacuities present; lack deciduous tooth
(dP3); lack fasciculus aberrans in forebrain (simplicicommissural); lack
superficial thymus; four or five mammae; adult females lack a pouch or
marsupium; ossified epipubic bones present; sperm paired; sperm rec-
tangular in shape; diploid chromosome number 2n = 14.

Known range. — Caenolestids are and according to the known fossil
record always have been endemic to South America.* Fossils are
known from beds of Casamayoran, Deseadan, Colhuehuapian, Santa-
crucian, Chasicoan, and Montehermosan age of Argentina, and from
Deseadan age beds of Bolivia. Living forms range along the Andes
Cordillera from southern Venezuela, through the uplands of Colombia,
Ecuador and Peru, south to Llanquihue Province and Chiloe Island in
southern Chile.

Comments. — The broader relationships of caenolestids with Aus-
tralasian groups are discussed by Osgood (1921), Ride (1962), and
Kirsch (1977a), and their relationships with other South American
groups are discussed by Paula Couto (1952b) and Simpson (1928, 1930,
1933, 1970, 1971).

The documented occurrence of Caenolestidae in beds of
Casamayoran age is based solely on an isolated lower molar (AMNH
28442), identified as an M, by Simpson (1948, p. 50). Simpson noted
that this tooth has no shear specializations; the paraconid is reduced
and is internal in position; the talonid is high and nearly bicuspid, with
the entoconid about equal to the metaconid; and the hypoconulid is
small and "sparlike."

This specimen was apparently broken subsequent to Simpson's
study, and only the talonid remains (fig. 3). The entoconid is slightly
larger than the hypoconid, and the hypoconulid is very reduced. This

*The African Miocene species Palaeothentoides africanus Stromer, 1932, was be-
lieved by its describer to be a caenolestoid and hence to have South American affinities.
Butler & Hopwood (1957) and Patterson (1965) have shown, however, that this species is
a member of the exclusively African placental family Macroscelididae.

32

FIELDIANA: GEOLOGY

Fig. 3. Caenolestid indet. (Casamayoran). AMNH 28442, a nearly complete talonid of
a right M,?: a, occlusal; b, labial; c, posterior; d, lingual views. Scale = 25X.

specimen does indeed appear to represent a caenolestid and is probably
a member of the subfamily Caenolestinae. Apart from this, little can be
said of its phylogenetic significance.

Several South American fossil taxa once classified as caenolestids or
believed to have had close caenolestid affinity have been shown to
either be nomina vana or to belong elsewhere.

Progarzonia notostylopense Ameghino, 1904b, p. 260, was based on
a fragment of a left mandibular ramus (MACN A55-14) with a single,
two-rooted P :! , 2.5 mm. in length, collected from beds of Casamayoran
age from the Barranca south of Lago Colhue-Huapi (Simpson, 1948, p.
50; 1967a, 1967b, p. 9). Simpson (1967b, p. 9) concluded that:

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 33

. . . the animal may be a caenolestid, but in my opinion it is not adequately identifi-
able at any taxonomic level below the class.

IPromy sops primarius Ameghino, 1902b, p. 36 (listed as Promysops
primarius by Ameghino, 1903, p. 89, fig. 6; 1906, p. 363, fig. 209) was
based on an isolated incisor (MACN A55-10) from the Musters Forma-
tion of Patagonia (no other data) (Simpson, 1948, p. 50; 1967b, p. 9).
Simpson (1948, p. 50) noted that this incisor is:

. . . somewhat gliriform, with the crown enameled and the enamel not extending

into the alveolus. It is perhaps from a caenolestid or a polydolopid, but even this is

not certain.

He (1967b, p. 9) later concluded that:

. . . this specimen does not belong to Promysops, which is a [junior] synonym of
[the polydolopoid genus] Eudolops. The specimen is not identifiable, and the specific
name is a nomen vanum.

Zygotes tes Ameghino, 1898, p. 243, was erected on the basis of
specimens collected from the Entre Rios Formation
("Mesopotamiense"), along the rio Parana, Entre Rios Province,
Argentina. These beds are now believed to be Late Tertiary (i.e.,
Huayquerian and Montehermosan) in age (see Marshall et al., In
press). Two species were recognized, and both were once placed in the
Caenolestidae (see table 1). Reig (1957) restudied these specimens and
demonstrated that they were both referrable to the family Didelphidae.
The type species, Zygolestes paranensis Ameghino, 1898, p. 243, was
based on a left mandibular ramus with P 2 -M 4 (MACN 8889). The
unique feature of this specimen (see Reig, 1957, p. 213, fig. 1) not found
in other known Didelphidae is the small relative size of the P :i com-
pared with the much larger P 2 and M,. A referred species, Zygolestes
entrerrianus Ameghino, 1899a, p. 7, was based on an isolated right M,
(MACN 8888). Reig has shown this species to be referrable to the living
didelphid genus Philander.

Subfamily CAENOLESTINAE (Trouessart, 1898, p. 1205)
Sinclair, 1906, p. 416 (= Caenolestidae Trouessart, 1898,
p. 1205, sensu stricto; Caenolestini Winge, 1923, p. 84)
(Including Garzonidae Ameghino, 1891b, p. 304)

Diagnosis. — I.^i,, C{, Pi, M:}; P 2 double rooted and functional; P. {
large, double rooted and equal to or greater than height of M, trigonid;
M\:\ tuberculo-sectorial, no lophs in unworn teeth; M, with prominent
metaconid, trigonid, and talonid regions unmodified; M 2 . : , with distinct
trigonids and talonids, talonid much larger in occlusal view than
trigonid; "intermediate conule" present at inner base of metacone on
M 13 ; M 1 quadritubercular; neither P\ M 1 , P 2 , nor M, are developed

34 FIELDIANA: GEOLOGY

into sectorials; antorbital vacuity present between nasal, maxillary,
and frontal.

Known range. — Casamayoran, Deseadan, Colhuehuapian, Santa-
crucian, Chasicoan, and Montehermosan of Argentina; Recent in
Chile, Colombia, Ecuador, Peru, and Venezuela.

Comments. — Living Caenolestinae are reviewed by Osgood (1924)
and discussed by Collins (1973), and fossil Caenolestinae are discussed
by Reig (1955), Marshall (1976b), Pascual & Herrera (1973, 1975), and
Marshall & Pascual (1977).

Tribe CAENOLESTINI (Trouessart, 1898, p. 1205)
Winge, 1923, p. 84

Diagnosis. — Differs from Pichipilini in trigonids of M 2 . 3 having two
large, distinct lingual cusps (paraconid and metaconid, respectively)
separated by deep valley; trigonid basin distinct; talonid basin narrow
and deep; absence of cuspule posterior to lingual trigonid cusp on M,_ 3 ;
trigonid cusps notably higher than talonid cusps.

Known range. — Casamayoran, Deseadan, and Santacrucian of
Argentina; Recent in Chile, Colombia, Ecuador, Peru, and Venezuela.

Includes. —

1. Caenolestes Thomas, 1895a, p. 367 [=Hyracodon Tomes, 1863, p.
50, nee Hyracodon Leidy, 1856, p. 91 (a genus of Perissodactyla)].

la. Caenolestes caniventer Anthony, 1921, p. 6. Recent — known

only from El Chiral, Cordillera Occidental, El Oro, Ecuador,
lb. Caenolestes convelatus Anthony, 1924, p. 1. Recent — known

only from Aloag and Las Maquinas, Cordillera Occidental,

Ecuador,
lc. Caenolestes fuliginosus (Tomes, 1863, p. 51). Recent — known

only from Andes of Ecuador.
Id. Caenolestes obscurus Thomas, 1895a, p. 367. Recent — known

only from Bogota northward along the Cordillera Oriental to the

Paramo de Tama on Venezuelan-Colombian border,
le. Caenolestes tatei Anthony, 1923, p. 1. Recent — known only

from Molleturo, Azuay, Cordillera Occidental, Ecuador.

2. Lestoros Oehser, 1934, p. 240 [=Orolestes Thomas, 1917, p. 3, nee
Orolestes MacLachlan, 1895, p. 21 (a genus of dragonfly); Cryp-
tolestes Tate, 1934, p. 154, nee Cryptolestes Ganglebauer, 1899, p.
608 (a subgenus of Coleoptera)].

2a. Lestoros inca (Thomas, 1917, p. 3). Recent — known only from
southern Peru.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 35

3. Pseudhalmarhiphus Ameghino, 1899a, p. 7.

3a. Pseudhalmarhiphus guaraniticus (Ameghino, 1899a, p. 7). De-
seadan.

4. Stilotherium Ameghino, 1887, p. 7 [Including Garzonia Ameghino,
1891b, p. 307; Halmarhiphus Ameghino, 1891b, p. 308 (partim);
Parhalmarhiphus Ameghino, 1894, p. 356].

4a. Stilotherium dissimile Ameghino, 1887, p. 7 [Including Garzonia
typica Ameghino, 1891b, p. 307; Garzonia annectens (partim)
Ameghino, 1891b, p. 307; Pichipilus exilis Ameghino, 1891b, p.
307; Garzonia captiva Ameghino, 1891b, p. 308; Garzonia
minima Ameghino, 1891b, p. 308; Halmarhiphus didelpoides
(sic) (partim) Ameghino, 1891b, p. 308; Halmarhiphus nanus
(partim) Ameghino, 1891b, p. 308; Phonocdromus patagonicus
(partim) Ameghino, 1894, p. 355.] Santacrucian.

5. Rhyncholestes Osgood, 1924, p. 169.

5a. Rhyncholestes raphanurus Osgood, 1924, p. 170. Recent —
known only from forests of Llanquihue Province and Chiloe
Island, southern Chile.

Remarks. — Included within the Caenolestini are the most gener-
alized of known Caenolestidae. They represent the prototype group
from which evolved the Pichipilini and the subfamilies Palaeothentinae
and Abderitinae. The Caenolestini have the longest known record of
any caenolestid group, extending from Casamayoran to Recent.

Pseudhalmarhiphus guaraniticus was erected by Ameghino (1899a,
p. 7) on the basis of a fragment of a right mandibular ramus with M,. 2 .
The present whereabouts of this, the type specimen, is not known,
although Ameghino (1899b, p. 560, fig. 5; 1902d, p. 424, fig. 5; 1903, p.
83, fig. 2) did figure the M 2 in three views. As figured by Ameghino, the
M 2 trigonid has two well-developed lingual cusps (paraconid and
metaconid) separated by a deep valley; the trigonid is only slightly
narrower than the talonid, and the cusps are sharp and high; the
trigonid and talonid basins are deep and narrow, and the tooth is very
narrow for its length; and a well-developed anterobasal cingulum is
present. Ameghino (1899a, p. 7) gave the length of M,. 2 (his M 4 . 5 ) as 3.5
mm. In all of these features, Pseudhalmarhiphus is structurally similar
to and is probably directly ancestral to Stilotherium dissimile (Mar-
shall, 1976b, p. 58).

Stilotherium dissimile (figs. 4, 5) is the most abundant caenolestine in
the Santacrucian fauna of Argentina. Reig (1955, p. 62) noted that he
was unable to locate the type; therefore, he selected MACN 8464 (fig.
6) as neotype. However, Ameghino recorded in his catalogue that

36

FIELDIANA: GEOLOGY

Fig. 4. Stilotherium dissimile Ameghino, 1887, p. 7 (Santacrucian). MACN 8427, a
fragment of a rostrum with left C, P 2 , and P 3 (same individual as in fig. 5): a, labial; b,
occlusal; c, lingual views. Scale - 5 mm.

MACN 5723, a fragment of a right mandibular ramus with crowns of
P 2 - 3 and bases of M,_ 2 , is the "Tipo," and this specimen agrees per-
fectly with the original description. MACN 5723 is recorded as being
collected by Carlos Ameghino in 1890-91, whereas the species S. dis-
simile was named four years earlier in 1887.* Whether this specimen is

*There are many uncertainties regarding Carlos Ameghino's 1887 collection. It is very
likely that all of it did not end up in the MLP, but that Florentino diverted a substantial
portion to the MACN. There may have been several shipments from Carlos, of which the
first one or two went to the MLP and served as the basis for Florentine's Enumeration
sistemdtica . . . of 1887, whereas the last one or two provided the basis for his monograph

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

37

me pa

hy pr

Fig. 5. Stilotherium dissimile Ameghino, 1887, p. 7 (Santacrucian). MACN 8426, a
fragment of a right maxillary with M 2 \ and MACN 8231, an isolated right M 1 (same
individual as in fig. 4): a, labial; b, occlusal; c, lingual views. Scale = 5 mm. Abbrevia-
tions are: pr, protocone; pa, paracone; me, metacone; ic, intermediate conule; hy,
hypocone.

of 1889 and went into the Ameghino Collection in the MACN, in which Bryan Patterson
(pers. comm.) and myself have seen some of the specimens there figured.

The evidence for this, as pointed out by Bryan Patterson {written communication,
Oct., 1975), is as follows. F. Ameghino resigned from the MLP on Jan. 17, 1888 (see
Ameghino, 1889, p. xiv), the culmination of a progressive deterioration of relations with
the director Alcedes Moreno, who thereupon barred Ameghino from the collections of
that institution. In February, 1888, Florentino began work on the "Contribucidn . . ."
and finished 14 months later (see Ameghino, 1889, p. vii), around April, 1889, as the
publication date was May 20 (1889, p. iv). His principal artist, Z. Bommert, worked for
eight straight months on that paper (see Atlas, pp. v-vi). In the course of this immense
labor, Bommert illustrated 74 of 120-odd species described in Ameghino (1887) and all of
the 11 additional species described in Ameghino (1889). Where did the material for all of
this come from? Certainly not from the MLP, because Moreno would never have allowed

38

FIELDIANA: GEOLOGY

Fig. 6. Stilotherium dissimile Ameghino, 1887, p. 7 (Santacrucian). MACN 8464
(neotype), a right mandibular ramus with complete dentition, missing only tip of I,: a,
labial; b, occlusal; c, lingual views. Scale = 5 mm.

access, and Ameghino specifically stated (1889, pp. xiii-xiv) that Moreno was indeed
responsible for the fact that a number of species were not figured. Not, it would seem
from Carlos' expedition of 1888-89, unless an unreported detour to the Rio Santa Cruz
was made, which seems unlikely as there would have been no reason to keep it quiet,
both brothers being by then no longer in the employ of the MLP.

In dealing with F. Ameghino, it is sometimes necessary to employ what may be termed
textual criticism, which in this instance compels one to the belief that all of the 1887
collection did not end up in the MLP. This was not simple robbery, at least in Floren-
tine's eyes. He had taken Moreno's measure and found him wanting, both as a man and
as a paleontologist. Ameghino may have decided that Science would be better served
with part of the collection in his possession — and, if he did, events have largely proved
him correct. Also, as one who had crucially aided the expedition of 1887 in various ways
(see 1889, p. xiv), Ameghino may well have thought he had a moral right to take such
action. In any event, the type of Stilotherium dissimile may well have been included
among those specimens "diverted" to the MACN.

Rosendo Pascual has also noted that after the MLP collections were closed to Floren-
tine Carlos went back to Patagonia and recollected the same localities that he worked in
1886-87. Some of these new specimens came to be labeled as types, in the MACN, of
species that he described in 1887.

This was Florentine's way of being able to refer to types, despite the fact that the real
types were in the MLP. Many of these supplemental MACN types were collected by
Carlos during his field season of 1890-91. Such may be the case of MACN 5723.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 39

in fact the type, and the dating in the catalogue is in error, or whether
this specimen is itself a neotype selected by Ameghino in 1891 is not
known. Reig's neotype is certainly more complete than the type of
Ameghino (sensu his catalogue), and in this respect it is a much more
useful specimen. Because there is some doubt as to the validity of
MACN 5723 being the true "Tipo," I follow Reig and recognize
MACN 8464 as the valid neotype (also see Marshall, 1976b, pp. 62-63
for discussion on this point).

Most of the synonymies recognized here for Stilotherium dissimile
were originally suggested by Reig (1955). My only modification from
his scheme is in recognizing Garzonia typica Ameghino, 1891b, p. 307
(type species of the genus) as a junior synonym of S. dissimile. Reig
(1955, p. 64) recognized "G." typica as a valid species of Stilotherium
and noted that S. dissimile and S. typicum were virtually identical in
size and structure and surely differed only in the greater depth of the
mandibular ramus in the latter. On the primary basis of this one
character he recommended tentatively regarding these taxa as distinct,
and I (1976b, p. 62) later followed this suggestion. Upon restudy of all
pertinent material, I now see no justification for recognizing these taxa
as distinct and here formally recognize them as synonymous. In addi-
tion, I formally recognize Pichipilus exilis Ameghino, 1891b, p. 307, as
a junior synonym of S. dissimile. P. exilis was based on a fragment of a
left mandibular ramus (MACN 5698) with alveoli of M 2 and M 4 , and M : ,
present but very worn.

A second species of Stilotherium, S. grande, was erected by
Ameghino (1894, p. 358) on the basis of what he believed to be a right
lower molar. Reig (1955, p. 64) was unable to locate the type, but
concluded that based on Ameghino' s description the species was not
related to Stilotherium nor was it a caenolestid. While in the MACN in
1976, I was fortunate to relocate the type (MACN 8468) in the
Ameghino collection. I gave a cast of this to P. Hershkovitz for study,
and he has demonstrated (unpubl.) that it represents the dP 4 of the
primate genus Homunculus and proposes to recognize it as a valid
species of that genus.

The validity of the three genera — Garzonia, Halmarhiphus,
Parhalmarhiphus — included in synonymy with Stilotherium was also
discussed by Reig (1955), the conclusions of which are substantiated by
my own studies. Reig (1955, p. 63) noted that Halmarhiphus di-
delphoides was based on four partial mandibular rami (MACN 5716,
5717, 5718, 5719) of which the first (considered the type in the MACN
catalogue) and the latter two are microbiotheres, whereas MACN 5717

40 FIELDIANA: GEOLOGY

is inseparable from S. dissimile. Halmarhiphus nanus (the genotype)
was based on three partial mandibular rami of which one (MACN
5720 — considered the type in the MACN catalogue) is inseparable from
S. dissimile, another (MACN 5721) is probably a microbiothere, and
the third is an edentulous mandibular ramus that on the basis of its size
may be referred to Phonocdromus gracilis.

The type species of Parhalmarhiphus Ameghino, 1894, p. 357, is
"Garzonia" annectens Ameghino, 1891b, p. 307. The type of that
species (MACN 5703) is a left mandibular ramus with M^ that is
inseparable from specimens of S. dissimile. However, the generic di-
agnosis of Parhalmarhiphus appears to have been based largely on two
other specimens — MACN 5704 and 5705 — of which the first is an in-
determinate caenolestid, and the second is a microbiothere. Con-
sequently, the genus Parhalmarhiphus has no validity (Reig, 1955, p.
63).

The living Caenolestini are grouped into three genera — Caenolestes,
Lestoros, Rhyncholestes — with five named species in the first and one
each in the others (Osgood, 1924). It is generally agreed among Recent
marsupial workers that the genus Caenolestes is overly split, and three
of the nominal species are known only from or near their type locality.
In addition, the genera Caenolestes and Lestoros are questionably
separable. Simpson (1970, p. 41n) has suggested that placing of the
"genera" as three species would be a better arrangement. Many addi-
tional species of Caenolestinae have been collected since the time of
Osgood's study, and the living forms are clearly in need of a rigorous
systematic revision.

Tribe PICHIPILINI new tribe

Diagnosis. — Differs from Caenolestini in trigonids being narrower
than talonids; single, large lingual trigonid cusp that is bifid in unworn
teeth (paraconid very reduced); trigonid cusps equal to or only slightly
higher than talonid cusps; talonid basin broad and relatively shallow;
cuspule present posterior to lingual trigonid cusp on M,. 3 ; P 3 small in
some taxa (Pliolestes), but large in others (Phonocdromus, Pichipilus).

Known range. — Colhuehuapian, Santacrucian, Chasicoan, and
Montehermosan of Argentina.

Includes. —

1. Pliolestes Reig, 1955, p. 66.

la. Pliolestes tripotamicus Reig, 1955, p. 67. Montehermosan.

2. Phonocdromus Ameghino, 1894, p. 355.

2a. Phonocdromus gracilis Ameghino, 1894, p. 356. Santacrucian.

MARSHALL: SYSTEM ATICS OF CAENOLESTIDAE 41

3. Pichipilus Ameghino, 1890, p. 155.

3a. Pichipilus osborni Ameghino, 1890, p. 155. Santacrucian.
3b. Pichipilus riggsi (Simpson, 1932, p. 4). Colhuehuapian.
3c. Pichipilus centinelus Marshall and Pascual, 1977, p. 102. Early
Santacrucian ("Notohipidense" horizon).

Comments. — Within the Pichipilini are several mid- to late Tertiary
taxa that include the largest and the smallest of known Caenolestinae.
In certain features of molar morphology (i.e., reduced size of paraconid
on M 2 . :{ ; trigonid cusps equal to or only slightly higher than talonid
cusps; talonid basin broad and relatively shallow) they resemble
Palaeothentinae.

The oldest known species is Pichipilus riggsi from the Colhuehua-
pian of Patagonia. This species was originally placed by Simpson (1932,
p. 4, fig. 2) in the genus Halmarhiphus. Reig (1955, p. 61) later noted
that it does not belong in Halmarhiphus, is possibly referable to
Phonocdromus or, more fundamentally, to a new genus. The generic
affinities of the species riggsi were clarified upon the redescription of
the Santacrucian species Pichipilus osborni by Marshall (1976b) and
the discovery and description of a new early Santacrucian species of
Pichipilus, P. centinelus by Marshall & Pascual (1977). The species
riggsi was formally placed in Pichipilus by Marshall & Pascual (1977).
The three known species of Pichipilus appear to represent an evolu-
tionary lineage characterized by slight size increase, going from the
smallest species P. centinelus in the Colhuehuapian to the largest
species P. osborni in the later Santacrucian, and with the early Santa-
crucian P. centineulus representing an intermediate form in size, struc-
ture, and time.

Pliolestes tripotamicus was erected by Reig (1955, p. 67, fig. 3) on
the basis of specimens from beds of Montehermosan age in Argentina.
The species was based on a fragment of a left mandibular ramus
(MACN 9971) with P 3 and M 2 present and alveoli of P,. 2 , M,. 2 , and part
of M 4 . Pascual & Herrera (1973, p. 42) later described additional
specimens of that species and referred a specimen (MMP 975M) from
the Arroyo Chasico Fm. (Chasicoan Age) to Pliolestes sp.

Species of Pichipilus and Pliolestes share a large number of features:
both are similar in size; anterobasal cingulum is large and broad;
trigonid has two major cusps, with the lingual cusp set anterior relative
to the labial cusp; trigonid is much narrower than the talonid; talonid
basin is broad and shallow; small hypoconulid present just posterior to
entoconid and joined with hypoconid by a low posterocingular ridge;
and overall proportions of known molar teeth are similar. In Pichipilus,

42

FIELDIANA: GEOLOGY

the P,j is small (i.e., it is about Vi the height of M, trigonid), and the
lingual corner of the anterobasal cingulum continues onto the anterior
surface of the trigonid as a small ridge, whereas in Pliolestes the P 3 is
about the same height as the M, trigonid, and there is no ridge along the
anterior surface of the trigonid. Because of these similarities,
Pichipilus represents an ideal morphological ancestor for Pliolestes,
and the last two features may be considered derived in Pliolestes.
Pichipilus and Pliolestes are the largest known genera of Caenoles-
tinae.

Phonocdromus gracilis is the smallest known species of Caenoles-
tinae (fig. 7) and is further distinguished from Pichipilus and Pliolestes

Fig. 7. Phonocdromus gracilis Ameghino, 1894, p. 356 (Santacrucian). MACN 8457
(lectotype), a fragment of a left mandibular ramus with P3-M3 complete, alveoli of M 4 : a,
labial; b, occlusal; c, lingual views. Scale = 5 mm.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 43

in its molars being proportionately narrower and more elongated an-
te roposteriorly; in the anterobasal cingulum being proportionately nar-
rower and less well developed; in the M 2 trigonid being proportionately
not as narrow as the talonid; and in the M :J trigonid being almost as
wide as the talonid (not distinctly narrower as in Pichipilus osborni).

Subfamily ABDERITINAE (Ameghino, 1889, pp. 268, 269)
Sinclair, 1906, p. 417
(Including Abderitesidae [sic]
Ameghino, 1889, pp. 268, 269;
Epanorthini Winge, 1923, p. 84 [partim])

Diagnosis. — 11, C\, PL MS; mandibular ramus short and deep; large
procumbent incisor (I,) followed by four tiny, spaced, single-rooted
vestigial teeth (I 2 , C, P,, P 2 ); P 2 single rooted; M, lacks metaconid,
trigonid transversely compressed, greatly elevated above rest of tooth
row, and modified into "plagiaulacoid" shear-blade with serrated edge
along crest joining protoconid and paraconid; M 2 : 3 bunolophodont,
distinct lophs connect primary labial and lingual cusps; M 2 . 3 lack
paraconid, trigonid and talonid of subequal size in occlusal view and in
height in lateral view, trigonid and talonid basins shallow; no trace of
"intermediate conule" on M 13 ; small cusp present anterior to paracone
on M 3 ; sectorials— P 3 (?)/P 3 -M, tri g„nid or MVM, trigonid-

Known range. — Deseadan, Colhuehuapian, and Santacrucian, Santa
Cruz and Chubut Provinces, Patagonia, southern Argentina.

Comments. — The species and genera of Abderitinae are reviewed by
Marshall (1976a).

Tribe PARABDERITINI new tribe

Diagnosis. — Mandibular ramus shallower and more gracile than in
Abderitini; P 2 separated from P ;J by distinct diastema; P., large, double
rooted, and blade-like, with simple serrated edge (up to two serrations
on each surface and corresponding apical denticles, with a smaller
anterior and a larger posterior); M, shear-blade, with two distinct ser-
rations on each surface and corresponding apical denticles; M, talonid
unmodified and similar to that on M 2 ; M 2 . ;} proportionately longer and
narrower than in Abderitini, and trigonids and talonids of M 2 . :1 distinct;
distinct cuspule absent just anterior to paracone on M 3 ; sectorials — P 3

(•)'P3"M, trigonid*

Known range. — Deseadan, Colhuehuapian, and early Santacrucian,
Santa Cruz and Chubut Provinces, Patagonia, southern Argentina.

Includes. —
1. Parabderites Ameghino, 1902c, p. 121 [Including Tideus Ameghino,

44

FIELDIANA: GEOLOGY

1890, p. 157, nee Tydeus Koch, 1837, Table II (Arachnida), nee Sauv-
age, 1870, p. 23 (Pisces), Tydaeus Ameghino, 1893a, p. 15; Mannodon
Ameghino, 1893a, p. 15.]

la. Parabderites bicrispatus Ameghino, 1902c, p. 121. Colhuehuapian.

lb. Parabderites minusculus Ameghino, 1902b, p. 43 Deseadan.

Comments. — Within the Parabderitini is included one genus,
Parabderites, with two species, P. minusculus (fig. 8) and P. bicris-

r-

Fig. 8. Parabderites minusculus Ameghino, 1902b, p. 43 (Deseadan). MACN 52-380
(type), a left mandibular ramus with P 3 -M 3 , and alveoli of M 2 : a, labial; b, occlusal; c,
lingual views. Scale = 5 mm.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

45

Fig. 9. Parabderites bicrispatus Ameghino, 1902c, p. 121 (Colhuehuapian). MACN
52-45 (type), greater part of a right mandibular ramus with alveoli of C-P 2 , P. t -M 4 com-
plete but worn: a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

patus (fig. 9). Parabderites minusculus is the smallest of the two and is
the only abderitine of Deseadan age. It is known only from its type
(MACN 52-380), a left mandibular ramus with P 3 -M 3 and alveoli
of M 4 (see Marshall, 1976a, p. 79, fig. 10; Patterson & Marshall,
1978, p. 89, fig. 22).

The Colhuehuapian species P. bicrispatus is known from several
specimens, including partial upper and relatively complete lower
dentitions (see Marshall, 1976a, p. 76). It differs from/ 1 , minusculus in
being larger in size, in having two distinct serrations on labial and
lingual sides of P 3 (P 3 off. minusculus has no serrations), and in the P :i
and trigonid region of M, being inclined forward at less of an angle
relative to the main horizontal axis of the mandibular ramus.

46 FIELDIANA: GEOLOGY

No morphological characters are present in P. minusculus that
would exclude it as an ancestor of P. bicrispatus. The change from one
to the other involves increase in size, development of serrations on the
P 3 , and the orientation of the P,$ and trigonid region of the M, into a
more vertical position. It is thus possible to regard P. minusculus as the
Deseadan ancestor of P. bicrispatus.

An isolated left M 2 (MACN 52- 375b) and a fragment of a right man-
dibular ramus with roots of M,_ 4 (MLP 68-1-17-205) identified as
Parabderites sp. are known from the "Notohipidense" horizon (early
Santacrucian) at Karaiken and Cerro Centinela near the eastern edge of
Lago Argentino, Patagonia (see Marshall, 1976a, p. 79, fig. 11; Mar-
shall & Pascual, 1977, p. 115, fig. 7). Both specimens are intermediate
in size between P. minusculus and P. bicrispatus, but because they are
found in beds younger than either of those species, they cannot repre-
sent a phylogenetic intermediate form. The poorly known
"Notohipidense" population of Parabderites thus may have evolved
directly from a form similar to P. minusculus or from a post-/*.
minusculus — pre-P. bicrispatus population of that genus.

The above molar (MACN 52-375b) referred by Marshall (1976a, p.
81) to Parabderites sp. was referred by Ameghino (see below) to his
species Tideus trisulcatus and Mannodon trisulcatus. To clarify the
previous taxonomic history of this tooth it is necessary to review the
history of these names.

Tideus trisulcatus was erected by Ameghino (1890, p. 157) on the
basis of a tip of a "lower incisor," described as having three longitudi-
nal sulci and being similar in size and shape to species of Abderites. It
was placed in the Plagiaulacoidea. The type of T. trisulcatus (MACN
52-375a) does not, however, appear to represent a mammal, but its true
affinities are not known. It can be described for all practial purposes as
a sliver of reddish-brown bone, with two deep longitudinal sulci (not
three as indicated by Ameghino), that measures 7.6 mm. in length. The
type is thus indeterminate, and the generic and specific names are
nomina vana.

Ameghino (1893a, p. 15) replaced the name Tideus with Mannodon
on the ground that it was doubly preoccupied by Tydaeus (misprint for
Tydeus Koch, 1837, a genus of Arachnida; Sauvage, 1870, a genus of
Pisces). The former spelling is, however, different from Tydeus and
this does not constitute preoccupation under the present Code. The
name Tideus is thus technically valid.

Ameghino (1893a, p. 15) also noted that Mannodon trisulcatus was
the first genus of Plagiaulacidae known from Patagonia in which the

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 47

"lower molar' ' was constructed similar to multituberculates. The
lower molar he referred to was MACN 52-375b, which he later figured
(1903, p. 110, fig. 28) and listed as coming from the "Notohipidense"
horizon in the figure caption. Ameghino' s concept of Tideus trisulcatus
(=Mannodon trisulcatus) was essentially based around this specimen,
and the type (i.e., the dubious lower incisor — MACN 52-375a) is not
discussed further by him except for a brief statement (1898, p. 185) to
its Santacrucian age. The most detailed description of this species and
one based solely on MACN 52-375b (the M 2 ) is given by Ameghino in
1894 (p. 340). In essence, the name Tideus trisulcatus was used by
Ameghino with reference to the type (MACN 52-375a), whereas the
name Mannodon trisulcatus was applied to the M 2 (MACN 52-375b).
The M 2 , however, is not the type that is anomen vanum, and there are
no problems of preoccupation of the generic name Parabderites
Ameghino, 1902c, by the older names Tideus Ameghino, 1890, or
Mannodon Ameghino, 1893a.

Tribe ABDERITINI (Ameghino, 1889, pp. 268, 269) new rank
(=Abderitesidae [sic] Ameghino, 1889, pp. 268, 269]

Diagnosis. — Mandibular ramus short and deep; P 2 not separated
from P., by distinct diastema; P., single rooted, styliform, and set in
notch in anterobasal edge of M,; M, shear-blade more highly spe-
cialized than in Parabderitini and with three to six apical denticles and
corresponding labial and lingual serrations, and talonid very reduced
but basined with lingual side enclosed by prominent, anteroposteriorly
compressed entoconid; M 2 . 4 proportionately shorter and broader than
in Parabderitini, and trigonids and talonids poorly differentiated in
worn teeth; M ;! slightly smaller than M 2 , and of similar shape and
structure; M 1 blade-like with serrated anterior edge; M 24 with two
distinct labial cusps (which are connected basally, forming a well-
developed anteroposterior crest), and two lower lingual cusps; distinct
cuspule occurs just anterior to paracone on M { ; sectorials — MV

Mi trigonid (fig- 10).

Known range. — Colhuehuapian and Santacrucian, Santa Cruz and
Chubut Provinces, Patagonia, southern Argentina.

Includes. —
1. Abderites Ameghino, 1887, p. 5 [Including Homunculites
Ameghino, 1902c, p. 73].

la. A bderites crispus Ameghino, 1902c, p. 120 [Including A bderites
crispulus Ameghino, 1902c, p. 120; Parabderites invelatus
Ameghino, 1902c, p. 122]. Colhuehuapian.

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MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 49

lb. Abderites meridionalis Ameghino, 1887, p. 5 [Including Abder-
ites crasignathus (sic) Ameghino, 1891a, p. 248; Abderites
crassiramis Ameghino, 1893b, p. 80; Abderites serratus
Ameghino, 1891a, p. 248; Abderites tenuissimus Ameghino,
1891b, p. 304]. Santacrucian.
lc. Abderites pristinus (Ameghino, 1902c, p. 73). Colhuehuapian.
2. Pitheculites Ameghino, 1902c, p. 74 [Including Eomannodon
Ameghino, 1902c, p. 119; Micrabderites Simpson, 1932, p. 6].
2a. Pitheculites minimus Ameghino, 1902c, p. 74 [Including
Eomannodon multitubergulatus (sic) Ameghino, 1902c, p. 119;
Micrabderites williamsi Simpson, 1932, p. 6]. Colhuehuapian.
Comments. — Included within the Abderitini are several mid-Tertiary
taxa that are characterized by possession of a large "plagiaulacoid" M,
with a serrated cutting edge and with P, very reduced, peg-like, and set
into a notch in the anterobasal edge of the M,.

Pitheculites minimus from the Colhuehuapian of Patagonia is the
smallest known species of Abderitini. It differs from species of Abder-
ites in its smaller size and in the M, blade having fewer striae [three
occur in Pitheculites (AMNH 29661) compared with six in Abderites]
(Marshall, 1976a, p. 72).

Three species of Abderites are recognized — A. crispus and A. pris-
tinus of Colhuehuapian age and A. meridionalis (fig. 11) of Santacru-
cian age. Abderites crispus and A. meridionalis are represented by
large sample sizes, and the numerous characters that can be compared
show them to be quite similar. In A. crispus, the Mj is larger in length
and breadth, Mill are smaller and the lophs connecting the labial and
lingual cusps are not as well developed, the M 2 is proportionately
shorter, and the labial crests in M 2 " 3 are proportionately stronger than
in A. meridionalis.

I recognize A. crispus as the probable Colhuehuapian ancestor of A.
meridionalis. The primary changes from one to the other include in-
crease in size of Ml::}, slight reduction in length and breadth of Mj, size
reduction of labial crests on M 2,J , increase in size of lophs connecting
labial and lingual cusps, and proportionate increase in length of M 2 .
These changes are minor, and there is little problem in deriving one
from the other.

The type of A. pristinus (MACN 52-34), a fragment of a left man-
dibular ramus with M 2 complete and alveoli of P.,, M, and M :{ . 4 , is all
that is known of this species, and little can be said about its affinities
with other species of Abderites. Abderites pristinus has a larger M 2 and
a more gracile mandibular ramus than either A. crispus or A.

50

FIELDIANA: GEOLOGY

Fig. U.Abderites meridionalis Ameghino, 1887, p. 5 (Santacrucian). MACN 2037, a
left mandibular ramus with alveoli of C-P,, P 2 -M., complete, M 4 missing anterolingual
corner: a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

meridionalis. It is certainly distinct from the other Colhuehuapian
species A. crispus, and it does not appear to be involved in the ancestry
of A. meridionalis.

The dentitions of A. crispus and P. minimus are similar in the weak
development of the lophs connecting the lingual and labial cusps, in the
shorter and more quadrate structure of M 2 as compared to the more
elongated M 2 in A. meridionalis, and in the large and prominent struc-
ture of the labial crest in M 2 and M 3 (especially M 2 ). These features are
all slightly modified in the Santacrucian A. meridionalis, and their joint
occurrence in the two Colhuehuapian taxa suggest that they represent
character states shared by a common Pitheculites-Abderites ancestor.

Abderites altiramis Ameghino, 1894, p. 304, was based on a right
mandibular ramus (MACN 8250) with the anterior alveolus and talonid
of M :? and both roots of M 4 , collected from the Santa Cruz beds of
Patagonia. This specimen was earlier figured by Ameghino (1889, pi. 1 ,

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 51

figs. 10- 10b) as "Epanorthus" aratae and has been shown by Marshall
(1976a, p. 72) to be a borhyaenid. The name Abderites altiramis repre-
sents a junior synonym of the borhyaenid species Perathereutes
pungens Ameghino, 1891b.

A specimen (MLP 68-1-17-210), consisting of a fragment of a left
mandibular ramus with alveoli and/or roots of most of the teeth, col-
lected from the "Notohipidense" horizon (early Santacrucian) of
Patagonia has been identified as Abderites sp. by Marshall & Pascual
(1977, p. 113).

Pascual & Odreman Rivas (1971, p. 396) include Abderites sp. in a
faunal list of Friasian mammals. However, no specimens of Abderites
have as yet been described from beds of Friasian age, and this report
needs confirmation and documentation.

Willard (1966, p. 73, pi. 65, fig. 6) identified a partial edentulous left
mandibular ramus with seven alveoli as Abderites sp. Judging from the
photograph presented by Willard, this specimen is a member of the
family Didelphidae as evidenced by the seven posterior alveoli that are
of subequal size and shape. In Abderites, these alveoli decrease rapidly
in size from front to back. The specimen is listed as coming from the
"upper Inuya" of Peru. These beds are presently regarded as Late
Tertiary (cf. Huayquerian and/or Montehermosan) in age (Marshall et
al., in press).

Subfamily PALAEOTHENTINAE Sinclair, 1906, p. 417
(Including Epanorthidae Ameghino, 1889,
pp. 268, 270, sensu s trie to;
Epanorthini Winge, 1923, p. 84 \partim]\
Decastidae Ameghino, 1893b, p. 79;
Epanorthinae Trouessart, 1905, p. 840;
Palaeothentidae Osgood, 1921, pp. 143, 151)

Diagnosis. — L], C{, P< 2 : !.- { ,, M:{; mandibular ramus long and relatively
shallow, but deeper and relatively shorter than in Caenolestinae; two
mental foramina are typically present, one below P 2 and another below
M,, sometimes a third occurs between these below anterior root of M, ;
large procumbent and lanceolate I, followed by three or four tiny,
vestigial teeth (I 2 , C, P,, P 2 ); P 2 either double or single rooted; P : , either
single rooted and styliform with a crown height less than Vi that of M,,
or large, double rooted, and equal to or greater than height of M,
trigonid (intermediate sizes also occur); M, with trigonid region (crest
connecting protoconid and paraconid) elongated and with paraconid
set far anteriad, metaconid large and well developed; Mf:;j brachyo-

52 FIELDIANA: GEOLOGY

dont, no distinct lophs in unworn teeth; trigonid and talonid regions of
M 2 . :! distinct and subequal in size in occlusal view and in height in
lateral view, trigonid and talonid basins shallow, paraconid absent; P 12
very reduced in size and crown height; P 2 laterally compressed with
prominent central cusp and smaller anterior and posterior accessory
cuspules; P 3 enormous, rivalling M 1 in size in some taxa, and with
crown height equal to or greater than that of M 1 ; posterior end of P 3
crown much broader than anterior and with posterolingual cingular
shelf; anterior root of P :i is much narrower transversely than posterior
root; sharp cutting edge formed along labial sides of M 12 and extending
onto P 3 ; M 1 with cingular shelf along anterior edge of paracone;
"intermediate conule" weakly developed in unworn M 1 " 3 only in P.
minutus; anterior ends of M 1 " 3 much broader than posterior ends;
sectorials-posterointernal surface of P 3 shears against labial surface of
M, trigonid; no trace of antorbital vacuity as in Caenolestinae.

Known range. — Deseadan, Colhuehuapian, and Santacrucian of
Patagonia, southern Argentina; Deseadan of Bolivia.

Comments. — Although 16 generic names for palaeothentines have
been proposed (15 based initially on Santacrucian species), their status
has been viewed as extremely dubious. This is due to the fact that
many of the type specimens were never figured, and diagnoses for the
most part were inadequate. The group has also suffered from neglect,
and the included genera and species were last reviewed by Ameghino
(1898).

Apart from Palaeothentes Ameghino, 1887, the first named, the gen-
era include Acdestis Ameghino, 1887; Epanorthus Ameghino, 1889 (a
replacement name for Palaeothentes); Dipilus Ameghino, 1890; De-
castis Ameghino, 1891; Callomenus Ameghino, 1891; Essoprion
Ameghino, 1891; Halmadromus Ameghino, 1891; Halmaselus
Ameghino, 1891; Palaepanorthus Ameghino, 1902c; Metriodromus
Ameghino, 1894; Metaepanorthus Ameghino, 1894; Paraepanorthus
Ameghino, 1894; Prepanorthus Ameghino, 1894; Cladoclinus
Ameghino, 1894; and Pilchenia Ameghino, 1903.

Subsequent workers agreed that the Palaeothentinae were overly
split at the generic and specific levels. Simpson (1945, p. 45), for exam-
ple, tentatively recognized only five genera {Palaeothentes, Pilchenia,
Acdestis, Dipilus, and Halmadromus). The others were either included
as synonyms of one of these five or were regarded nomina vana. As
Simpson (1945, p. 42, 2n) noted:

Proper generic criteria for this group have not yet been worked out, and the pub-
lished data are inadequate in several cases.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 53

All of the genera and included species were erected on lower den-
titions and were distinguished in large part on the basis of overall size,
number of antemolar teeth, absolute size and/or number of roots on P :{ ,
relative size of P ? and M,, and presence, absence, and/or relative size
of accessory cuspules on P 3 * (see p. 29 for quote from Ameghino,
1898). Supposed differences in proportions of M,_ 4 were also occasion-
ally noted. These criteria alone or together are adequate if one is
working with entire dentitions, but for most taxa this was not the case.
In addition, Ameghino made no attempt to evaluate individual varia-
tion within a species, and the taxonomic limits of the species and
genera were never subjected to rigorous cross evalution based on large
sample sizes.

Palaeothentes Ameghino, 1887

Palaeothentes Moreno, 1882, p. 122 (nomen nudum).

Palaeothentes Ameghino, 1887, p. 5.

Epanorthus Ameghino, 1889, p. 271; to replace Palaeothentes.

Essoprion Ameghino, 1891b, p. 306.

Halmadromus Ameghino, 1891b, p. 306.

Halmaselus Ameghino, 1891b, p. 306.

Palaepanorthus Ameghino, 1902c, p. 123.

Metriodromus Ameghino, 1894, p. 342.

Metaepanorthus** Ameghino, 1894, p. 348.

Paraepanorthus** Ameghino, 1894, p. 349.

Prepanorthus Ameghino, 1894, p. 350.

Cladoclinus Ameghino, 1894, p. 358.

Pilchenia Ameghino, 1903, p. 128.

Type of Palaeothentes. — P. aratae Ameghino, 1887, p. 5.

Type of Epanorthus. — E. aratae (Ameghino, 1889, p. 272).

Type of Essoprion. — E. coruscus Ameghino, 1891b, p. 306.

Type of Halmadromus. — H. vagus Ameghino, 1891b, p. 306.

Type of Halmaselus. — H. valens Ameghino, 1891b, p. 306.

Type of Palaepanorthus. — P. primus Ameghino, 1902c, p. 123.

Type of Metriodromus. — M. arenarus Ameghino, 1894, p. 343.

Type of Metaepanorthus. — M. intermedius Ameghino, 1887, p. 6.

*For example, Metaepanorthus was characterized by the presence of a well-defined
anterior and posterior accessory cuspule on P :i , and Paraepanorthus, by the occurrence
of the anterior cuspule only.

**In accordance with Articles 27 and 32c of the International Code of Zoological
Nomenclature (Stoll et al., 1961, 1964) the diacritic mark is dropped from the names
originally spelled Metaepanorthus and Paraepanorthus.

54 FIELDIANA: GEOLOGY

Type of Paraepanorthus. — P. minutus (Ameghino, 1894, p. 350).
Type of Prepanorthus. — P. lanius Ameghino, 1894, p. 351.
Type of Cladoclinus. — C. copei Ameghino, 1894, p. 359.
Type of Pilchenia. — P. lucina Ameghino, 1903, p. 128.

Diagnosis. — Small to very large Palaeothentinae: If, Cj, P 3 , Mi; P 2
reduced relative to P 3 and double or single rooted; P 3 large, double
rooted (posterior root is always larger than anterior root), and always
greater than x /i height of M, trigonid; anterobasal cuspule present on P 3 ;
paraconid bifurcated on M,; M, protoconid is generally slightly higher
than paraconid in unworn teeth compared with species of Acdestis in
which they are generally more subequal in height; anterolabial cingula
weakly developed on M,. 2 ; anterobasal cuspule on P 5 well developed in
unworn teeth; size decrease from Ml to M\ more gradual than in
species of Acdestis.

Known range. — Deseadan, Colhuehuapian, and Santacrucian of
Patagonia, southern Argentina; Deseadan of Bolivia.

Comments. — The name "Palaeothentes aratae Mor." was pub-
lished in a list of names by Doering (1882, p. 455) and is a nomen
nudum. In the same year Moreno (1882, p. 116) published the name
Palaeotenthes (also spelled by him Palaeothentes) aratae but this too
is a nomen nudum. It is impossible to establish which name appeared
first. A valid definition of this genus and species was first published by
Ameghino (1887, p. 5) under the name Palaeothentes. In 1889
Ameghino (p. 271) decided that the spelling Palaeothentes was "im-
posible" and that the generic name should have been written
Palaeoteuthis and hence was preoccupied by Palaeoteuthis D'Orbigny
(1850, p. 327), an extinct genus of dibranchiate cephalopod. On these
grounds, Ameghino (1889, p. 271) proposed the generic name Epanor-
thus to replace Palaeothentes Ameghino, 1887. But the spelling
Palaeothentes was original, intentional, and has priority and ipso facto
is the correct spelling regardless of its etymology; it cannot be pre-
occupied by the quite different name Palaeoteuthis (Simpson, 1945, p.
45n). Indeed, Sinclair (1906, p. 416) has already argued that Epanor-
thus:

. . . can no longer be retained either for a genus or to designate a family [Epanor-
thidae].

There is no possible origin for the name Palaeothentes. Palmer (1904)
gave "thereutes, hunter" as the origin and probably got that from
Ameghino. However, it is impossible to get -thentes or anything like it
from -thereutes.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 55

Palaeothentes, when described in 1887 (and redescribed in 1889
when Epanorthus was proposed to replace it), contained six species,
although no type-species was designated on either occasion. Clemens
& Marshall (1976, p. 72) were the first to designate a type-species when
they chose P. aratae, the first species described.

Eight species of Palaeothentes are here recognized: three {P. lucina,
P. boliviensis, P. chubutensis) are known from beds of Deseadan age,
one (P. primus) is from beds of Colhuehuapian age, and four {P.
minutus, P. intermedius, P. lemoinei, P. aratae) are from the Santa-
crucian.

These species are distinguished primarily on the basis of absolute
size and on minor size differences of the P :J relative to the M, (figs.
12-17). For example, in length of M,. 4 (fig. 12) all species for a given
Age are readily separable one from the other. This is also true for plots
of L P, vs. L M, (fig. 13), L M, vs. W M, (fig. 14), and L M, vs. L M 2
(fig. 15). These plots are based for the most part on large sample sizes,
and they show that absolute and/or relative size differences alone are
ample to readily differentiate the species.

Palaeothentes minutus Ameghino, 1887. Figures 18-20; Tables 3-5.

Palaeothentes minutus Ameghino, 1887, p. 6; Sinclair, 1906, p. 432, pi. 63, figs. 1,

4-5a, pi. 64, fig. 2; Schlosser, 1925, p. 27, figs. 40B, 42.
Epanorthus minutus Ameghino, 1889, p. 274, pi. 1, fig. 16; 1893b, p. 78, fig. 1.
Paraepanorthus minutus Ameghino, 1894, p. 350, fig. 40; 1897, p. 500, fig. 76; 1898, p.

186, fig. 50h; 1904a, p. 45, fig. 30; 1905, p. 17, figs. 18, 19; Rusconi, 1933, p. 247, fig.

4.
Paraepanorthus (Epanorthus) minutus Ameghino. 1903, p. 141, figs. 62, 95, 96.
Dipilus bergii Ameghino, 1890, p. 155; 1894, p. 342; 1898, p. 186.
Halmaselus valens Ameghino, 1891b, p. 306; 1894, p. 351; 1898, p. 186.
Essoprion consumptus Ameghino, 1891b, p. 306; 1894, p. 351; 1898, p. 186.
Essoprion coruscus Ameghino, 1891b, p. 306; 1894, p. 351; 1898, p. 186.
Epanorthus simplex Ameghino, 1894, p. 347.

Cladoclinus copei Ameghino, 1894, p. 359; 1903, p. 117, fig. 35; Reig, 1955, p. 64.
Epanorthus delicatus Ameghino, 1894, in Roger, 18%, p. 19 (nomen nudum).
Palaeothentes delicatus Simpson, 1930, p. 57 (nomen nudum).
Metaepanorthus complicatus Ameghino, 1894, p. 348; 1898, p. 186.
Epanorthus complicatus Roger, 18%, p. 19.
Palaeothentes complicatus Sinclair, 1906, p. 455.
Prepanorthus lanius Ameghino, 1894, p. 351.

Type of Palaeothentes minutus. — MACN 15, a right mandibular
ramus with alveoli of I 2 -P 2 , and P 3 -M 4 complete (listed as type in
Ameghino's catalogue).

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FIELDIANA: GEOLOGY

Fig. 18. Palaeothentes minutus Ameghino, 1887, p. 6 (Santacrucian). MACN 15
(type), a right mandibular ramus with alveoli of L-P 2 , and P ;j -M 4 complete: a, labial; b,
occlusal; c, lingual views. Scale = 5 mm.

Type of Dipilus bergii. — MACN 2041 , a fragment of a left mandibular
ramus with P 3 -M 2 .

Type of Halmaselus valens. — MACN 6595, a fragment of a right
mandibular ramus with alveoli of C-P 2 , P :! -M 2 complete (the alveoli of
the P 2 show this tooth to have been double rooted, a character not
visible if the tooth were present).

Type of Essoprion consumptus. — MACN 5697, a fragment of a right
mandibular ramus with alveoli of I 2 -P 2 , PrM, complete, and trigonid of
M 2 present.

Type of Essoprion coruscus. — MACN 5696, a fragment of a right
mandibular ramus with alveoli of C-M l5 and M 2 complete.

Type of Epanorthus simplex. — MACN 5677, a fragment of a left
mandibular ramus with alveoli of P,_ 2 , and P 3 -M 2 complete (listed as
type in Ameghino' s catalogue).

Type of Epanorthus delicatus. — MACN 5690, a fragment of a left
mandibular ramus with alveoli of M 2 , and M : ,. 4 complete.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

63

Fig. 19. Palaeothentes minutus Ameghino, 1887, p. 6(Santacrucian). MACN 10245, a
left maxillary fragment with P'-M 4 complete: a, labial; b, occlusal; c, lingual views. Scale
= 5 mm.

Type of Epanorthus complicatus. — MACN 5671, a nearly complete
left mandibular ramus with base of I,, alveoli of I2-P2. P.i complete,
alveoli of M,, and M 2 . 4 complete.

Type of Prepanorthus lanius.— MACN 8323-8328 [8323, a fragment
of a right maxillary with M 1 * 3 complete; 8324, a fragment of a left
maxillary with M 2 ' complete, and alveoli of M 1 and M 4 ; 8325, a frag-
ment of a right maxillary with P 1 :! complete; 8326, two isolated upper
incisors; 8327, three isolated upper molars; 8328, a pelvic fragment
with acetabulum (all of a single associated individual)].

64

FIELDIANA: GEOLOGY

Fig. 20. Palaeothentes minutus Ameghino, 1887, p. 6. Left lateral view of skull.
Redrafted from Ameghino (1897, fig. 76; 1903, figs. 62, 95; 1904a, fig. 30). This figure was
drawn by Florentino Ameghino and is apparently based in total or at least in part on
MACN 8271. Scale = 3 X natural size.

Type ofCladoclinus copei. — MACN 8469, a fragment of a right man-
dibular ramus with M 4 complete.

Hypodigm. — The 10 types and MACN 2042, a fragment of a right
mandibular ramus with M ; $_ 4 (possible cotype of Dipilus bergii); MACN
5672, a fragment of an innominate (supposedly of same individual as
type of Epanorthus complicatus, MACN 5671); MACN 5673, a right
mandibular ramus with P :! -M,; MACN 5674, a right mandibular ramus
with P :J ; MACN 5675, a right mandibular ramus with P 3 -M 2 ; MACN
5674, a right mandibular ramus with P :? ; MACN 5675, a right mandibu-
lar ramus with P a ; MACN 5676, a fragment of a right mandibular ramus
with P.rM,; MACN 8271, partial skull with attached mandible with
complete dentition, including incisors (this is probably the specimen
used by Ameghino to reconstruct the skull that he illustrated — see
Ameghino, 1897, fig. 76; 1903, figs. 62, 95; 1904a, fig. 30— as it is the
most complete specimen of that element yet known); MACN 8297, a
nearly complete right mandibular ramus with dentition; MACN 8298,
nearly complete left mandibular ramus with dentition (this specimen
was figured by Ameghino, 1894, fig. 40; 1898, fig. 50h; 1903, fig. 96— it
is the same individual as 8297); MACN 8300, a left mandibular ramus
with P, complete, alveoli of M,, and M 2 . 4 complete; MACN 8306, a
right mandibular ramus with M,. 4 complete; MACN 8307, a right man-
dibular ramus with P 3 -M 4 complete; MACN 8308, a right mandibular
ramus with M 2 . 4 complete; MACN 8309, a right ramus with M 2 _ 4 com-
plete; MACN 8310, a left mandibular ramus with M,_ 2 complete;
MACN 8321, a right maxillary fragment with P ;5 -M' 5 complete; MACN
8330a, a fragment of a left mandibular ramus with P 3 -M 3 complete;
MACN 8330b, a fragment of a right mandibular ramus with I,-M, (same
individual as 8330a); MACN 8331, a left mandibular ramus with I,-M 2

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66

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

67

Table 5. Statistics for some cheek teeth of Palaeothentes minutus.

Dimension

N

OR

X

s

cv

Upper cheek teeth

pa

L

2

1.6-1.9

1.75

0.21

12.00

W

2

1.1-1.3

1.20

0.14

11.67

M'

L

4

2.0-2.3

2.18

0.15

6.88

W

4

1.8-2.2

1.98

0.17

8.59

M 2

L

6

1.6-1.9

1.73

0.14

8.09

W

6

1.8-2.1

1.97

0.10

5.08

W

L

6

1.0-1.3

1.12

0.15

13.39

W

6

1.5-1.7

1.63

0.08

4.91

w

L

3

0.8-0.9

0.87

0.06

6.90

W

3

1.2-1.3

1.27

0.06

4.72

M IJ

L

3

5.8-6.3

6.03

0.25

4.15

P*-M 4

L

2

7.7-8.0

7.85

0.21

2.68

Lower cheek teeth

P:,

L

24

1.0-1.3

1.12

0.12

10.71

W

24

0.7-1.0

0.84

0.07

8.33

Mi

L

23

2.2-2.7

2.45

0.17

6.94

W

23

1.2-1.5

1.36

0.08

5.88

M,

L

24

1.8-2.2

1.93

0.13

6.74

W

25

1.3-1.5

1.40

0.07

5.00

Ma

L

19

1.4-1.8

1.54

0.14

9.09

W

19

1.1-1.3

1.21

0.06

4.%

M 4

L

17

0.9-1.1

1.01

0.06

5.94

W

18

0.8-1.0

0.88

0.06

6.82

M,. 4

L

12

6.9-7.8

7.27

0.26

3.58

P :r M 4

L

6

8.1-8.6

8.37

0.21

2.51

complete; MACN 8355, rostral and palatal region of skull with partial
dentition; MACN 8372, partial skull with attached mandible (mandible
has greater part of dentition but lacks incisors; left half of skull with
P*-M 4 complete); MACN 8376, a left mandibular ramus with P 3 -M,
complete; MACN 8377, a left mandibular ramus with P.rM, (same
individual as 8376); MACN 10245, a left maxillary fragment with P'-M 4
complete (labeled D. spegazzinii); MACN 10246, rostral part of skull
with partial dentition; AMNH 9122, a fragment of a left mandibular
ramus with P.rM, complete; AMNH 9599, a left mandibular ramus with
M,. 4 complete; KUVP 655, a left mandibular ramus with I,-C complete,
alveoli of P,-P 2 andP 3 -M 4 complete, and an associated right mandibular
ramus with I,, alveoli of I 2 -P,, P2 complete, and P.rM., complete (only
M 2 is broken between trigonid and talonid); PU 15068, a fragment of a
right mandibular ramus with P.rM., complete, and alveoli of M 4 ; PU
15624, an incomplete mandibular ramus; PU 15706, a left mandibular
ramus with I,, alveoli of I 2 -Pj, P 2 complete, P :J complete, roots of M,,

68 FIELDIANA: GEOLOGY

M 2 . 4 complete; PU 15707, a fragment of a right mandibular ramus with
base of I,, alveoli of I 2 -P 2 , P :! -M 2 complete; PU 15708, a left mandibular
ramus with I,, alveoli of I 2 -P 2 , and P 3 -M, complete (only posterior edge
of M, is broken); PU 15709, a fragment of a right mandibular ramus
with I,-C, a fragment of a left mandibular ramus with I,, alveoli of I 2 -P 2 ,
P;, complete, anterior half of M, present, alveoli of M 2 , M 3 . 4 complete,
and an associated fragment of a left maxillary with P :i -M 4 complete; and
PU 15999, a fragment of a right maxillary with M 2:i complete; MLP
11-51, a fragment of a left mandibular ramus with M 2 . 3 complete and
alveoli of M 4 ; MLP 1 l-55a, a fragment of a left mandibular ramus with
M,_ 2 complete, and roots of M 3 ; MLP 11-123, a fragment of a left
mandibular ramus with P 3 -M 3 complete, and alveoli of M 4 ; MLP 11-
124, a fragment of a right mandibular ramus with alveoli of P 2 -M,, and
with M 2 complete; MLP 1 1-128, a fragment of a left mandibular ramus
with P ;! complete, and alveoli of P,. 2 and M,. (In addition to the above,
Ameghino, 1889, pi. 1 , fig. 16, figured a fragment of a mandibular ramus
with M,. 3 , and in 1905, figs. 18, 19, he figured an astragalus and cal-
caneum, respectively. I have not been able to locate or identify these
specimens in the Ameghino collection in the MACN.)

Horizon and locality. — All of the specimens are from the Santa
Cruz Formation, Santa Cruz Province, southern Argentina, and their
localities of collection are as follows: Killik Aike PU 15068 (collected
by O. A. Peterson, 1896), PU 15624 (collected by J. B. Hatcher, 1898),
PU 15706 (collected by H. Felton, 1899), PU 15707, 15708, 15709 (col-
lected by H. Felton, 1899); [La] Cueva MACN 8297, 8298, 8300, 8469,
10246 (collected by C. Ameghino, 1892-93); Santa Cruz MACN 15,
MLP 11-51, ll-55a, 11-123, 11-124, 11-128; Sehuen MACN 5677 (col-
lected by C. Ameghino, 1890-91); Rio Gallegos AMNH 9122, 9599
(collected by B. Brown, 1899); Monte Observation MACN 8323-28,
8321 (collected by C. Ameghino, 1891-92), MACN 5671, 5672, 5673,
5674, 5675, 5676, 5690, 5696, 5697, 6595, 8306, 8307, 8308, 8309, 8310
(collected by C. Ameghino, 1890-91); south side of Rio Santa Cruz, 60
miles below Lago Argentino PU 15999 (collected by J. B. Hatcher,
1897); KUVP 655, collected in 1904 by H. T. Martin from his "Loc.
S.A. 2."; MACN 2041 and 2042, collected by C. Ameghino, 1889-90
(locality not specified); MACN 10245, collected by C. Ameghino, 1898
(locality not specified); all other specimens are without collection or
locality data.

Age. — Santacrucian.

Diagnosis. — Smallest and most generalized of known Palaeothen-
tinae; molars relatively narrower and more trenchant than in other
known species; P 2 double rooted in some specimens; P, { large, double

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 69

rooted and = or > height of M,; anterobasal cuspule on P., large; P 1
double rooted; anterobasal cuspule on P 3 large; differs from con-
temporaneous P. intermedins in being smaller in size with a relatively
larger P, and with relatively narrower and more trenchant molars (fig.
17).

Comments.— Ameghino (1897, fig. 76; 1903, figs. 62, 95; 1904a, fig.
30) figured a nearly complete skull of Palaeothentes minutus, lacking
only the basicranial region. This illustration is apparently based in total
or at least in part on MACN 8271 and is here reproduced in Figure 20.
The rostral portion of the skull in MACN 8271 is no longer intact, and
the illustration thus documents our only knowledge of the upper in-
cisors and canine of the Palaeothentinae.

As seen in Figure 20, there are three single-rooted upper incisors
designated I 1 , I 2 , P. The I 1 is largest and is proodont; I 2 is lower and is
elongated anteroposteriorly; and I 3 is slightly higher than I 2 and is
button shaped. The I 1 and I 2 are similar to those in living Caenoles-
tinae, whereas the I 3 is more elongated and is thus more similar to I 2 in
living forms. The C is similar to the I 3 , but is slightly larger.

Palaeothentes primus (Ameghino, 1902c). Figure 21; Tables 6, 7.

Palaepanorthus primus Ameghino, 1902a, p. 77 (nomen nudum); 1902c, p. 123.

Type. — MACN 52-373a, a nearly complete edentulous left mandibu-
lar ramus.

Hypodigm. — MACN 52-370c, a fragment of a right mandibular
ramus with alveoli of P 2 , and P, { complete; MACN 52-373b, a fragment
of a left mandibular ramus with roots of P. { , M,.. { complete, and alveoli
of M 4 (possible cotype); MACN 52-373c, a complete lower left I,;
MACN 52-373d, root of a lower I,; MACN 52-377a, a right mandibular
ramus with alveoli of P 2 , P.rM :! complete, and alveoli of M 4 ; MMP
M-944, a right mandibular ramus with alveoli of I,-P 2 , roots of P ;r M,
and M 2 . 4 complete; MLP 77-V1-13-2, a fragment of a right mandibular
ramus with M,. 2 very worn; MLP 77-VI-13-16, a fragment of a left
mandibular ramus with M,. 2 complete; MLP 77-VI-13-17, a right man-
dibular ramus with P. { -M 4 complete; MLP 77- VI- 13-22, a left mandibu-
lar ramus with alveoli of C-P 2 and M, and M 4 , and with P., and M 2 . 3
complete.

Horizon and locality. — All specimens are from the Colhue-Huapi
Formation at the Barranca south of Lago Colhue-Huapi, Chubut
Province, Argentina. The MACN specimens were collected by C.
Ameghino; the MMP specimen (labeled "frente a estacion ferrocarril
La Parada") was collected by G. Scaglia, Contreras, and J. Hernandez
in 1964; the MLP specimens were collected by E. Herrera.

70

FIELDIANA: GEOLOGY

Fig. 21. Palaeothentes primus Ameghino, 1902c, p. 123 (Colhuehuapian). MACN
52-377a, a right mandibular ramus with alveoli of P 2 and M 4 , and P :i -M :! complete: a,
labial; b, occlusal; c, lingual views. Scale = 5 mm.

Age . — Colhuehuapian.

Diagnosis. — Small to medium-sized palaeothentine; P ;! large, double
rooted and = or < height of M,; differs from Palaeothentes inter-
medins in having slightly larger linear molar dimensions and in a rela-
tively larger P.,; differs from Acdestis oweni in having a much larger P :!
(fig. 17).

Comments. — In the same box containing the type (MACN 52-377a)
is another specimen (MACN 52-377b), a fragment of a left mandibular
ramus with alveoli of M :i _ 4 . The M 4 alveoli of this specimen are larger
than in known specimens of Palaeothentes primus; differences in the
posterior part of the mandible suggest that it is not referable to that

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71

72 FIELDIANA: GEOLOGY

Table 7. Statistics for some lower cheek teeth of Palaeothentes primus.

Dimension N OR x s CV

P, L 2 1.5 1-50

W 2 1.2-1.3 1.25 0.07 5.60

M L 2 3.6-3.8 3.70 0.14 3.78

W 2 2.1-2.2 2.15 0.07 3.26

M, L 3 2.5-2.7 2.57 0.12 4.67

W 3 1.9-2.1 2.03 0.12 5.91

M , L 3 1.9-2.0 1.97 0.06 3.05

W 3 1.5-1.6 1.53 0.06 3.92

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W 1 1-2 1-20

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P^M.L 4 11.2-12.0 11.60 0.37 3.19

species. Ameghino made no specific reference to this specimen, and it
is so fragmentary as to be virtually indeterminate. The name
Palaepanorthus secundus was included, along with Palaepanorthus
primus, by Ameghino (1902a, p. 77) in a faunal list of Colhuehuapian
species. This species was not then nor was it subsequently described,
and the name is a nomen nudum. As a point of speculation, Ameghino
may have coined this name for MACN 52-377b, but later decided not
to, or simply forgot to, formally describe it.
Palaeothentes intermedius Ameghino, 1887. Figures 22, 23; Tables 8, 9.

Palaeothentes intermedius Ameghino, 1887, p. 6 {not Sinclair, 1906, p. 430, pi. 63, figs.

3, 7, pi. 64, figs. 1, la); Schlosser, 1925, p. 27, fig. 40A; Simpson, 1930, p. 58.
Epanorthus intermedius Ameghino, 1889, p. 274, pi. 1, fig. 15.
Metaepanorthus intermedius Ameghino, 1894, p. 348.
Epanorthus lepidus Ameghino, 1891b, p. 305; 1894, p. 348.
Palaeothentes lepidus Sinclair, 1906, p. 431, pi. 62, figs. 6, 6a.
Epanorthus inaequalis Ameghino, 1891b, p. 305; 1894, p. 348; 1898, p. 186.
Palaeothentes inaequalis Sinclair, 1906, p. 455.
Halmadromus vagus Ameghino, 1891b, p. 306; 1894, p. 344; 1898, p. 186; Palmer,

1904, p. 307.
Metriodromus arenarus Ameghino, 1894, p. 343.
Dipilus arenarus Clemens & Marshall, 1976, p. 70.
Metriodromus crassidens Ameghino, 1898, p. 186.
Dipilus crassidens Clemens & Marshall, 1976, p. 71.

Epanorthus lemoinei (partim) Ameghino, 1894, figs. 36, 37; 1898, figs. 50e, f.
Type oiPalaeothentes intermedius.— MACN 2, a fragment of a right
mandibular ramus with P 3 -M 3 complete (figured by Ameghino, 1889, pi.
l.fig. 15).

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

73

Fig. 22. Palaeothentes intermedius Ameghino, 1887, p. 6 (Santacrucian). MACN 5678
(type oVEpanorthus lepidus"), a left mandibular ramus with alveoli of C-P 2 , and P :1 -M 4
complete: a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

Type of Epanorthus lepidus. — MACN 5678, a left mandibular ramus
with P3-M4 complete (listed as type in Ameghino's catalogue).

Type of Epanorthus inaequalis. — MACN 5689, a fragment of a left
mandibular ramus with M, complete, and alveoli of M 2 . 4 .

Type of Halmadromus vagus. — MACN 5694, a fragment of a left
mandibular ramus with alveoli of P 3 -M 3 .

Type of Metriodromus arenarus. — MACN 5699, a fragment of a right
mandibular ramus with M : , complete, and alveoli of M 2 and M 4 .

Type of Metriodromus crassidens. — MACN 8508, a right mandibular
ramus with P 3 and M 2 complete, and alveoli of M, and M 3 . 4 .

74

FIELDIANA: GEOLOGY

Fig. 23. Palaeothentes intermedius
Ameghino, 1887, p. 6 (Santacrucian).
MACN 5646, a fragment of a left maxil-
lary with M i:i complete: a, labial; b,
occlusal; c, lingual views. Scale = 5 mm.

Hypodigm. — The six types and MACN 2063, a fragment of a left
mandibular ramus with M,_ 2 complete (listed as type off. intermedius
in Ameghino's catalogue and a possible cotype); MACN 5582, a nearly
complete right mandibular ramus with I, and P 3 -M 3 complete; MACN
5584, a fragment of a right mandibular ramus with roots of M, and
anterior half of M 2 , and talonid of M 2 and M :! . 4 complete; MACN 5585,
a fragment of a right mandibular ramus with alveoli of M, and M 2 . 4
complete; MACN 5646, a fragment of a left maxillary with M 1 " 3 com-
plete (figured as P. lemoinei by Ameghino, 1894, figs. 36, 37; 1898, figs.
50e, f); MACN 5681, a fragment of a right mandibular ramus with
alveoli of I 2 -P 2 and P ;r M, complete; MACN 5682, a fragment of a left
mandibular ramus with P r M, complete; MACN 5683, a fragment of a
left mandibular ramus with P ;{ and M 2 complete, and alveoli of M,;

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76 FIELDIANA: GEOLOGY

Table 9. Statistics for some lower cheek teeth of
Palaeothentes intermedius.

Dimei

ision

N

OR

X

s

cv

P 3

L

11

1.1-1.3

1.24

0.08

6.45

W

11

0.8-1.2

1.01

0.12

11.88

M,

L

12

3.4-3.9

3.50

0.15

4.29

W

11

1.7-1.9

1.80

0.06

3.33

M 2

L

13

2.4-2.8

2.53

0.13

5.14

W

14

1.8-2.0

1.86

0.08

4.30

M :!

L

11

1.5-2.1

1.87

0.16

8.56

W

11

1.3-1.5

1.45

0.08

5.52

M 4

L

4

1.1-1.3

1.20

0.12

10.00

W

3

1.0-1.1

1.03

0.06

5.83

Mm

L

6

9.2-9.7

9.52

0.17

1.79

P,-M,

i L

5

10.5-10.9

10.68

0.15

1.40

MACN 8296, a fragment of a left mandibular ramus with P 3 -M! com-
plete, and trigonid of M 2 (very worn) (labeled E. simplex); MACN
8302, a right mandibular ramus with base of I,, alveoli of C-M,, and
M 2 _ 4 complete (labeled M. intermedius); MACN 8311, a fragment of a
left mandibular ramus with alveoli of M, and M 4 , and M 2 . 3 complete
(labeled M. complicates); NMNH 5937 (=AMNH 9596), a right man-
dibular ramus with P 3 complete, M, missing labial surface, M 2 com-
plete, and roots of M 3 _ 4 ; AMNH 9597, a right mandibular ramus with
P3-M3 complete (figured by Sinclair, 1906, pi. 63, fig. 6); AMNH 9598, a
left mandibular ramus with posterior half of P 3 , M,_ 3 complete, and
alveoli of M 4 ; AMNH 9600, a left mandibular ramus with P 3 -M 3 com-
plete; MLP 11-48, a fragment of a left mandibular ramus with M,_ 3
complete and alveoli of M 4 ; MLP 1 1-53, a fragment of a right mandibu-
lar ramus with posterior root of P 3 and anterior root of M,, talonid of
M, and M 2 complete but very worn; MLP 1 1-127, a fragment of a right
mandibular ramus with M 2 . 4 complete; MLP 11-131, a fragment of a
right mandibular ramus with P 3 -M,; MLP 55-XII-13-150, a right man-
dibular ramus with P 3 -M 3 complete and alveoli of M 4 .

Horizon and locality. — All specimens are from the Santa Cruz For-
mation, Santa Cruz Province, Patagonia, southern Argentina, and their
localities of collection are as follows: Santa Cruz MACN 2, MLP 11-
127, 11-131; Sehuen MACN 5689 (collected by C. Ameghino, 1890-91);
[La] Cueva MACN 8302, 8508 (collected by C. Ameghino, 1892-93);
Monte Observacion MACN 5582, 5584, 5585, 5646, 5678, 5681, 5682,
5683, 5694, 5699, 8311 (collected by C. Ameghino, 1890-91), MACN
8296 (collected by C. Ameghino, 1891-92); Rio Gallegos NMNH 5937,
AMNH 9597, 9598, 9600 (collected by B. Brown, 1899); Monte Leon

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 77

MLP 55-XII-13-150; MACN 2063 (collected in 1889-90, no additional
locality data); MLP 11-48, 11-53 (no data).

Age . — Santacrucian .

Diagnosis. — Small to medium-sized palaeothentine; P :1 large, double
rooted, less than height of M,; differs from Palaeothentes primus in
being slightly smaller in size and with a smaller P :} ; differs from P.
minutus in being larger and with a slightly smaller P.,; differs from
Acdestis oweni in being slightly smaller in linear tooth dimensions and
with a much larger P., (fig. 17).

Comments. — Palaeothentes intermedius has slightly larger linear
molar dimensions and a relatively larger P ; , than the Colhuehuapian
species P. primus. These differences are minor, and the two species
appear to represent a single phylogenetic lineage. I therefore recognize
P. primus as the probable Colhuehuapian ancestor of P. intermedius.

Palaeothentes lucina (Ameghino, 1903). Figure 24; Table 10.

Pilchenia lucina Ameghino, 1903, p. 128, fig. 49; 1904b, p. 259 said to be new in 1904,

but publication in 1903 was prior and valid); Loomis, 1914, p. 222, fig. 146.
Palaeothentes lucina Patterson & Marshall, 1978, p. 82, fig. 18.

Type.— MACN 52-371, an isolated left M,.

Hypodigm. — Type and AC 3110, a left mandibular ramus with P :!
missing anterior tip, and M 14 nearly complete.

Horizon and locality. — The type is from the "Piroteriense," Prob-
ably from Cabeza Blanca; AC 3110 is definitely from that locality.

Age . — De seadan .

Diagnosis. — Compared with Palaeothentes chubutensis and P.
boliviensis, P, { similar in relative length compared to M,, but consid-
erably narrower and lower; larger than in Acdestis praecursor; de-
crease in size from M, to M A more gradual than in P. chubutensis;
differs from P. lemoinei in being slightly smaller in overall linear tooth
dimensions but with a larger P., (fig. 17).

Comments. — Ameghino erected Pilchenia lucina on an isolated
molar that Loomis (1914) correctly interpreted as M ;j . Loomis assigned
a second specimen (AC 3110), consisting of the greater part of a left
mandibular ramus, to this species. I agree with this assignment.

When he proposed Pilchenia, Ameghino did not present criteria that
would distinguish it from any of the 15 named Colhuehuapian and
Santacrucian genera of Palaeothentinae. I have compared AC 3110
with a large sample of Santacrucian species of Palaeothentes and find
no reason to recognize it as distinct at the generic level; I therefore
assign lucina to that genus.

78

FIELDIANA: GEOLOGY

Fig. 24. Palaeothentes lucina (Ameghino, 1903, p. 128) (Deseadan). AC 3110, a left
mandibular ramus with P :t -M 4 : a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

Ameghino (1903, p. 128) based Pilchenia lobata on a fragment of a
right mandibular ramus with a complete M 2 (MACN 52-379). This
specimen was collected from the "Notohipidense" (early Santacru-
cian) horizon at Karaiken, near the eastern end of Lago Argentino,
Santa Cruz Province, Argentina. As noted by Marshall & Pascual
(1977, p. 113), this specimen is clearly referable to Palaeothentes and is
here regarded as conspecific with P. lemoinei from the Santa Cruz beds
along the Atlantic coast between Rio Gallegos in the south and Monte
Leon in the north.

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80

FIELDIANA: GEOLOGY

Fig. 25. Palaeothentes lemoinei Ameghino, 1887, p. 6 (Santacrucian). MACN 8293, a
nearly complete left mandibular ramus with alveoli of C-P 2 , and 1 12 and P. r M 4 complete:
a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

Palaeothentes lemoinei Ameghino, 1887. Figures 25, 26; Tables 11-13.

Palaeothentes lemoinei Ameghino, 1887, p. 6.

Epanorthus lemoinei Ameghino, 1889, p. 273, pi. 1, figs. 13, 14; 1890, fig. 7; 1894, p.

346, fig. 38; 1898, p. 186, fig. 50 g.
Epanorthus ambiguus Ameghino, 1891b, p. 305; 1894, p. 347; 1898, p. 186.
Palaeothentes ambiguus Sinclair, 1906, p. 454.
Epanorthus holmhergi Ameghino, 1890, p. 157, fig. 8.
Metaepanorthus holmhergi Ameghino, 1894, p. 349, fig. 39; 1898, p. 186; 1903, p. 172

(partim); Schlosser, 1925, p. 27, fig. 51A, B.
Palaeothentes holmhergi Sinclair, 1906, p. 455.
Callomenus ligatus Ameghino, 1903, p. 88 (partim, figs. 10 & 46 are referable to P.

lemoinei).
Pilchenia lobata Ameghino, 1903, p. 128, fig. 50; 1904b, p. 259 (said to be new in 1904,

but publication in 1903 was prior and valid).
Palaeothentes lobata Marshall & Pascual, 1977, p. Ill, fig. 6.
Type of Palaeothentes lemoinei. — MACN 3, a right mandibular
ramus with M,. 4 complete but worn (figured by Ameghino, 1889, pi. 1,
fig. 13; 1890, fig. 7; 1894, fig. 38; 1898, fig. 50g).

Type of Epanorthus ambiguus. — MACN 5565, a fragment of a right
mandibular ramus with M 2 - 4 complete.

: ».•: -•'■v./ .

Fig. 26. Palaeothentes lemoinei Ameghino, 1887, p. 6 (Santacrucian). MACN 5568, a
fragment of a left maxillary with P'-M 3 complete, and alveoli of M 4 : a, labial; b, occlusal;
c, lingual views. Scale = 5 mm.

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82

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

83

Table 13. Statistics for some cheek tooth dimensions of Palaeothentes lemoinei.

Dimension

N

OR

X

s

cv

Upper cheek teeth

F

L

2

3.0-3.3

3.15

0.21

6.67

W

2

2.0-2.2

2.10

0.14

6.67

M'

L

4

3.5-3.8

3.70

0.14

3.78

W

4

3.3-3.6

3.40

0.14

4.12

M 2

L

3

2.7-2.9

2.83

0.12

4.24

W

3

3.4-3.7

3.57

0.15

4.20

M :1

L

2

1.9

1.9

W

2

2.6-2.7

2.65

0.07

2.64

M 4

L

1

1.5

1.5

W

1

2.0

2.0

M 14
Lowei

L
t CHEEK teeth

1

10.0

10.0

p,

L

9

1.9-2.2

2.03

0.11

5.42

W

9

1.3-1.6

1.41

0.11

7.80

M,

L

11

4.4-4.8

4.54

0.16

3.52

W

11

2.2-2.5

2.32

0.11

4.74

M,

L

16

3.2-3.7

3.34

0.16

4.79

W

15

2.3-2.6

2.44

0.10

4.10

M :t

L

13

2.5-2.8

2.58

0.08

3.10

W

13

1.9-2.2

2.03

0.08

3.94

M,

L

7

1.6-1.9

1.79

0.13

7.26

W

7

1.3-1.6

1.46

0.10

6.85

M M

L

9

12.0-12.8

12.36

0.30

2.43

P,M 4

L

6

14.0-15.0

14.42

0.38

2.64

Type of Epanorthus holmbergi. — MACN 2071, originally a right
mandibular ramus with P :r M 4 complete [now in two parts — anterior
with P ; i through trigonid of M 2 , posterior with M :M complete; anterior
part, which had I, and diastema with alveoli of I 2 -P 2 has been lost since
specimen was figured by Ameghino (1890, fig. 8; 1894, fig. 39)].

Type of Pilchenia lobata. — MACN 52-379, a fragment of a right
mandibular ramus with M 2 .

Hypodigm. — The four types and FMNH P15264, a fragment of a left
mandibular ramus with P :r M, complete, and M 2 missing posterolabial
corner; MACN 4, a fragment of an M 1 (figured by Ameghino, 1889, pi.
1, fig. 14); MACN 5568, a fragment of a left maxillary with P :, -M 3
complete and alveoli of M A : MACN 5570, a left mandibular ramus with
P ;r M 4 complete (crown of M, broken): MACN 5571 , a fragment of a left
mandibular ramus with M,. 4 complete; MACN 5572, a fragment of a
right mandibular ramus with P. r M, complete; MACN 5576, a fragment
of a right maxillary with M 1 2 complete; MACN 5577, a fragment of a
left maxillary with M 14 complete; MACN 5578, a fragment of a right

84 FIELDIANA: GEOLOGY

maxillary with P J -M', and alveoli of M 2 ; MACN 8259, a fragment of a
right mandibular ramus with M 2 .;5 (M 3 is now loose from mandible;
originally referred in literature to C. ligatus — figured by Ameghino,
1903, figs. 10, 46); MACN 8291, a left mandibular ramus with P,-M 4
complete but worn (labeled E. ambiguus); MACN 8292, a right man-
dibular ramus with P ;r M 4 (labeled E. ambiguus); MACN 8293, a nearly
complete left mandibular ramus with nearly complete dentition (labeled
E. lemoinei); MACN 8294, a right mandibular ramus with P 3 -M 3 com-
plete, and roots of M 4 (labeled E. lemoinei); MACN 8295, a left man-
dibular ramus with complete I,, alveoli of I 2 -P 2 , and P 3 -M 4 complete;
MACN 10244, a right mandibular ramus with base of I,, alveoli of I 2 -P 2 ,
and P3-M2 complete; MLP 11-52, a fragment of a right mandibular
ramus with alveoli of M,, M 2 complete, alveoli of M 3 _ 4 ; MLP 11-56, a
fragment of a right mandibular ramus with alveoli of C-P 2 and with P 3
complete; MLP 1 1-129, a fragment of a right mandibular ramus with I,
and P 3 complete, and alveoli of I 2 -P 2 ; MLP55-XII-13-147, a fragment of
a left mandibular ramus with P 2 -M, complete; MLP 68-1-17-208, a
fragment of a right mandibular ramus with M 2 . 3 complete and roots of
M 4 ; and MLP 68-1-17-209, a fragment of a right mandibular ramus with
M 2 _ 3 complete, but broken.

Horizon and locality. — All specimens are from the Santa Cruz For-
mation, Santa Cruz Province, Patagonia, southern Argentina, and their
localities of collection are as follows: Corriguen-Kaik MACN 8291
(collected by C. Ameghino, 1892-93); [La] Cueva MACN 8292, 8294,
8295 (collected by C. Ameghino, 1892-93); Santa Cruz MACN 3, 4,
MLP 11-129; Quequa-Quemada MACN 8293 (collected by C.
Ameghino, 1892-93); Sehuen MACN 5565, 5568 (collected by C.
Ameghino, 1890-91); Monte Leon MLP 55-XII-13-147; Monte Obser-
vation MACN 5570, 5571, 5572, 5576, 5577, 5578 (collected by C.
Ameghino, 1890-91); MACN 10244 (collected by C. Ameghino,
1891-92); 12 miles North of Cape Fairweather FMNH P15264;
Karaiken MACN 52-379 (collected by C. Ameghino, 1889); Cerro Cen-
tinela MLP 68-1-17-208, 68-1-17-209 (collected by R. Pascual and O. E.
Odreman Rivas, 1968); MACN 2071 (collected in 1889-90— no locality
data); MACN 8259, MLP 11-52, 11-56 (no data).

Age . — Santacrucian .

Diagnosis. — Medium to large-sized palaeothentine; P :1 ~ in height to
M x ; M 3 larger than in Acdestis oweni and with relatively larger
hypocone; intermediate in size between contemporaneous P. inter-
medius and P. aratae; differs from Deseadan P. lucina in being slightly
larger in overall linear tooth dimensions but with a smaller P 3 (fig. 17).

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 85

Comments. — Palaeothentes lemoinei is similar in size and structure
to the Deseadan species P. lucina. They differ in the latter being
slightly smaller in overall linear tooth dimensions and in having an
absolutely larger P, t . These differences are, however, minor, and these
species are here regarded as representing a single phylogenetic lineage.
I recognize P. lucina as the probable Deseadan ancestor of P. lemoinei.

Palaeothentes boliviensis Patterson & Marshall, 1978. Figure 27; Table
10.

Palaeothentes boliviensis Patterson & Marshall, 1978, p. 83, fig. 19.

Type. — PU 21977, a fragment of a right mandibular ramus with P.,-M,
(posterolingual corner of M, is missing).

Horizon and locality. — Salla-Luribay Basin (BraniSa locality V-2),
Bolivia.

Age. — Deseadan.

Diagnosis. — Large palaeothentine; P :} ~ in height to M, trigonid;
smaller than Palaeothentes chubutensis; considerably larger and with
more prominent and higher-crowned P, 5 than contemporaneous P.
lucina and Acdestis praecursor (fig. 17).

Comments. — Palaeothentes boliviensis is the only palaeothentine
known from the Salla fauna, and it is the the only palaeothentine yet
known outside of Patagonia. In its relatively large size and high, broad
P 3 , P. boliviensis shows closer affinities to P. chubutensis than to any
other known Deseadan palaeothentine. Except for the very large San-
tacrucian species P. aratae, P. boliviensis is considerably larger than
any other known Colhuehuapian or Santacrucian palaeothentine.
Palaeothentes chubutensis (Ameghino, 1897). Figure 28; Table 10.

Epanorthus chubutensis Ameghino, 1897, p. 500, fig. 77.
Palaepanorthus chubutensis Ameghino, 1902a, p. 77.

Palaeothentes chubutensis Loomis, 1914, p. 221, fig. 145; Patterson & Marshall, 1978,
p. 85, fig. 20.

Type. — MACN 52-378, a right mandibular ramus with posterior root
of P 2 , P3-M2, and M 4 complete, roots of M :? (all teeth are heavily worn).

Hypodigm. — Type only.

Horizon and locality. — Chubut Province, Argentina; exact locality is
not known, but probably from Cabeza Blanca.

Age. — Deseadan.

Diagnosis. — Largest known species of pre-Santacrucian
Palaeothentinae; P : , = in height to M, trigonid; differs from similar-
sized Santacrucian Palaeothentes aratae in having a slightly deeper,
more robust mandibular ramus and a large P :! (fig. 17).

Fig. 27. Palaeothentes boliviensis Patterson & Marshall, 1978, p. 83 (Deseadan). PU
21977 (type), a fragment of a right mandibular ramus with P^-M, (posterolingual corner of
M, talonid is missing): a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

86

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

87

Fig. 28. Palaeothentes chubutensis (Ameghino, 1897, p. 500) (Deseadan). MACN
52-378 (type), a right mandibular ramus with posterior root of P 2 , P 3 -M 2 . and M 4 relatively
complete, and roots of M., (all teeth are heavily worn): a, labial; b, occlusal; c, lingual
views. Scale = 5 mm.

Comments. — Ameghino (1897, fig. 77) figured the type of
Palaeothentes chubutensis in which M :! was correctly illustrated as
missing. Loomis (1914, fig. 145) redrafted Ameghino's figure and in so
doing restored the missing tooth.
Palaeothentes aratae Ameghino, 1887. Figures 29, 30; Tables 14, 15.

Palaeothentes aratae Moreno, 1882, p. 122 (nomen nudum).

Palaeothentes aratae Ameghino, 1887, p. 5; Sinclair, 1906, p. 428, text-fig. 8, pi. 63,
figs. 2, 2a; J. L. Kraglievich, 1953, p. 54, fig. 6D.

Epanorthus aratae Ameghino, 1889, p. 272, pi. 1, figs. 10-12; 1894, p. 347.

Type. — MACN 14, a right mandibular ramus with alveoli of P,. 2 ,
P. r M 4 complete (figured by Sinclair, 1906, text-fig. 8; J. L. Kraglievich,
1953, fig. 6D).

Hypodigm. — MACN 1340 (cast), a right mandibular ramus with
roots of P,_, { , M,_ 2 present but worn, and roots of M : ,_ 4 (figured by
Ameghino, 1889, pi. 1, fig. 11-1 la; original probably in MLP); MACN

88

FIELDIANA: GEOLOGY

Fig. 29. Palaeothentes aratae Ameghino, 1887, p. 5 (Santacrucian). MACN 14 (type),
a right mandibular ramus with alveoli of P,. 2 , and P :t -M 4 complete: a, labial; b, occlusal; c,
lingual views. Scale = 5 mm.

5563, a fragment of a left mandibular ramus with P 3 -M 2 complete, and
MACN 5564, a complete associated left I,; MACN 5566, a fragment of
a left mandibular ramus with P ; <; MACN 8289, a right maxillary frag-
ment with roots of P 12 , space for P 3 , and M 1 " 3 complete; MACN 8290, a
fragment of a right mandibular ramus with alveoli of I 2 -P 2 (which de-
crease in size anteriorly), P 3 -M 3 complete, and alveoli of M 4 ; AMNH
9549, a right maxillary fragment with alveoli of P 1 , P 23 complete,
alveoli of M 1 , and M 24 complete; MLP 11-93, a fragment of a right
mandibular ramus with trigonid of M 3 present and roots of C-M,,
talonid of M 2 , and M 3 . 4 .

Horizon and locality. — All specimens are from the Santa Cruz For-
mation, Santa Cruz Province, Patagonia, southern Argentina, and their
localities of collection are as follows: Santa Cruz MACN 14 (collected
by C. Ameghino, 1890-91); Sehuen MACN 5563, 5564, 5566, 8289
(collected by C. Ameghino, 1890-91); Monte Observation MACN 8290
(collected by C. Ameghino, 1890-91); Rio Gallegos AMNH 9549 (col-
lected by B. Brown, 1899); MACN 1340 and MLP 11-93 (without lo-
cality data).

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

89

Fig. 30. Palaeothentes aratae Ameghino, 1887, p. 5 (Santacrucian). AMNH 9549, a
right maxillary fragment with alveoli of P 1 and M 1 , and F" 3 and M 2 ' complete: a, labial; b,
occlusal; c, lingual views. Scale = 5 mm.

Age. — Santacrucian.

Diagnosis. — Largest known species of Santacrucian palaeothentine
and only known species with single-rooted P 1 ; P :! ~ in height to M,
trigonid; teeth anterior to Pjj are more spaced than in other species;
differs from similar-sized Deseadan P. chubutensis in having a slightly
shallower and less robust mandibular ramus and a slightly smaller P,
(fig. 17).

i

2,

<N —

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ci ci

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ci ci r\i r\i

cheek teet

8289

9549*

CHEEK TEE

14

5563

5566

8290

II

m

ri

II

Upper i
MACN
AMNH

Lower
MACN
MACN
MACN
MACN

a.
*

90

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 91

Table 15. Statistics for some lower cheek teeth of Palaeothentes aratae.

Dmitri'

iion

.N

OR

X

s

cv

P,

L

4

2.6-3.2

2.93

0.25

8.53

W

4

2.0-2.3

2.10

0.14

6.67

M,

L

3

6.3-6.6

6.43

0.15

2.33

W

3

3.2-3.3

3.23

0.06

1.86

M,

L

3

4.3-4.4

4.33

0.06

1.39

W

3

3.1-3.2

3.17

0.06

1.89

M,

L

2

3.1

3.1

W

2

2.5

2.5

Comments. — The specimen figured by Ameghino (1889, pi. 1, fig.
10- 10b) as Epanorthus aratae is MACN 8250. It was later made the
type of Abderites altiramis by Ameghino (1894, p. 304) and was
characterized as being almost twice as large as Abderites crassiramis.
The specimen is, however, not an abderitine, but a small borhyaenid.
The size of the roots of M :i . A and structure of the M :$ talonid agree
perfectly with the type of Perathereutes pungens (MACN 684), which
is also of Santacrucian age. The ramus of A. altiramis is slightly shal-
lower and more gracile than that of P. pungens, but these differences
are minor, and they surely represent no more than individual variation
within a single species. The name A. altiramis thus represents a junior
synonym of Perathereute s pungens Ameghino, 1891b, the latter having
three years date of priority over the former (see Marshall, 1976a, p. 72).
In addition, the cranial roof fragment (MACN 1074) figured as
Epanorthus aratae by Ameghino (1889, pi. 1, figs. 12-12a) is not of a
marsupial, but more probably represents a dasypodid edentate.

Palaeothentes aratae is very similar to the Deseadan P. chubutensis
and can be regarded as a direct descendant of that species. The primary
changes involved in this lineage include a slight reduction in size and
robustness of the mandibular ramus and in size of the P 3 .

Acdestis Ameghino, 1887

Acdestis Ameghino. 1887, p. 5.
Dipilus Ameghino, 1890, p. 153.
Decastis Ameghino, 1891b, p. 305.
Callomenus Ameghino, 1891b, p. 306.

Type of Acdestis. — A. oweni Ameghino, 1887, p. 5.
Type of Dipilus. — D. spegazzinii Ameghino, 1890, p. 154.
Type of Decastis. — D. columnaris Ameghino, 1891b, p. 305.
Type of Callomenus. — C. intervalatus Ameghino, 1891b, p. 306.

92

FIELDIANA: GEOLOGY

Diagnosis. — Medium-sized Palaeothentinae; I|, Cj, P. 2 . ;? , M4 [three or
four teeth (I 2 , C, P,, P 2 ) on diastema between I, and P 3 ; P 2 sometimes
lost]; P :{ very small and ranging from double rooted and Vi height of M,
trigonid to single rooted and less than V2 height of M, trigonid; an-
terobasal cuspule absent on P 3 ; M, paraconid not bifurcated; an-
terobasal cuspule on P 3 very tiny; hint of development of stylar area
especially labial to M 2 paracone and less so labial to M 1 and M 2
metacone; size decrease from M 2 to M4 sharper, and M, relatively
larger and narrower than in species of Palaeothentes.

Known range. — Deseadan and Santacrucian of Patagonia, southern
Argentina.

Acdestis praecursor (Loomis, 1914). Figure 31; Table 10.

Callomenus praecursor Loomis, 1914, p. 223, figs. 147, 148.

Fig. 3 1 . Palaeothentes praecursor (Loomis, 1914, p. 223) (Deseadan). AC 3020 (type),
a fragment of aright mandibular ramus with crown of M 2 and alveoli of P 2 -M,: a, labial; b,
occlusal; c, lingual views. Scale = 5 mm.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 93

Acdestis praecursor Pascual & Odreman Rivas, 1971, p. 383; Clemens & Marshall,

1976, p. 69.
Palaeothentes praecursor Patterson & Marshall, 1978, p. 87, fig. 21.

Type. — AC 3020, a fragment of a right mandibular ramus with M 2 .
The crowns of P. ? and M,, originally present, have been lost since the
specimen was figured by Loomis.

Hypodigm. — Type only.

Horizon and locality . — Cabeza Blanca, Chubut Province, Argentina.

Age. — Deseadan.

Diagnosis. — P ; , double rooted, very small compared with that of
other Deseadan species, about half as high as M, trigonid; M,. 2 slightly
larger than in Palaeothentes lucina, considerably smaller than in P .
boliviensis and P. chubutensis; M, and M 2 slightly longer than in San-
tacrucian species Acdestis oweni (fig. 17).

Comments. — M,. 2 of Acdestis praecursor are heavily worn, pre-
venting comparison of minor cusp morphology with Palaeothentes
lucina. The smaller size of M,. 2 and larger size of P. { in the latter serve
to separate these species. Acdestis praecursor has the smallest P., of
any known Deseadan Palaeothentinae.

Acdestis oweni Ameghino, 1887. Figures 32-34; Tables 16-18.

Acdestis oweni Ameghino, 1887, p. 5; 1889, p. 270, pi. 1, fig. 9; 1890, p. 153, fig. 4;

1894, p. 342, fig. 33; 1898, p. 186, fig. 50d; 1903, p. 171, fig. 98.
Dipilus spegazzinii Ameghino, 1890, p. 154, figs. 5, 6; 1894, p. 342, figs. 34, 35; 1898, p.

186, fig. 50a, b.
Dipilus spegazzinianus Ameghino, 1903, pp. 157, 172, figs. 79, 99.
Acdestis elatus Ameghino, 1891b, p. 304; 1894, p. 342; 1898, p. 186.
Acdestis parvus Ameghino, 1891b, p. 305; 1894, p. 342; 1898, p. 186.
Callomenus intervalatus Ameghino, 1891b, p. 306; 1894, p. 344.
Callomenus ligatus Ameghino, 1894, p. 344; 1903, p. 88 (partim), fig. 5 (figs. 10 & 46

are referable to Palaeothentes lemoinei); Sinclair, 1906, p. 435, pi. 64, figs. 5, 5a.
Callomenus robustus Ameghino, 1894, p. 344; 1903, pp. 116, 120, figs. 34, 38; Schlos-

ser, 1925, p. 28, fig. 43.
Decastis columnaris Ameghino, 1891b, p. 305; 1893b, p. 79, fig. 3; 1894, p. 341, fig. 32;

1898, fig. 50c; 1903, p. 171, fig. 97; Sinclair, 1906, p. 437, pi. 64, figs. 4, 4a, 6, 6a.
Decastis rurigenus Ameghino, 1891b, p. 305; 1894, p. 342; 1898, p. 186; Sinclair, 1906,

p. 452.
Dipilus rurigenus Clemens & Marshall, 1976, p. 71.
Metriodromus spectans Ameghino, 1894, p. 343; 1898, p. 186.
Dipilus spectans Clemens & Marshall, 1976, p. 71.
Metaepanorthus holmbergi Ameghino, 1903, p. 172 {partim), fig. 100.
Palaeothentes intermedins Sinclair, 1906, p. 430, pi. 63, figs. 3, 7, pi. 64, figs. 1, la.

94

FIELDIANA: GEOLOGY

Fig. 32. Acdestis oweni Ameghino, 1887, p. 5 (Santacrucian). MACN 5559 (type of
"Acdestis elatus"), a left mandibular ramus with alveoli of L-P 2 , and P. ( -M, complete: a,
labial; b, occlusal; c, lingual views. Scale = 5 mm.

Type of Acdestis oweni. — MACN 1379, a fragment of a right man-
dibular ramus with root of I,, alveoli of I0-P2, P.vM, complete, and
trigonid of M, present (figured by Ameghino, 1889, pi. 1, fig. 9-9e; 1890,
fig. 4; 1894, fig. 33; 1898, fig. 50d; and probably 1903, fig. 98— in the
latter four publications, the jaw was partially restored by the artist,
with I,-P 2 being added).

Type of Dipilus spegazzinii. — MACN 2038, a left mandibular ramus
(greatly restored) with complete 1,-P, , P 3 -M 2 complete, in position of
M.< trigonid is a reversed right M, talonid (the jaw is completely re-
stored in this area, resulting in an increase and exaggeration of distance
from M, to M 4 ), posterior half of M ;! and all of M A are complete (figured
by Ameghino, 1890, figs. 5, 6; 1894, figs. 34, 35; 1898, fig. 50a, b; 1903,
figs. 79, 99 — the P., is actually larger relative to the M, than appears as
figured; crown of P, is actually about twice the size of the crowns of
I 2 -P 2 ).

Type of Acdestis elatus. — MACN 5559, a left mandibular ramus with
alveoli of I 2 -P 2 , and P. r M 4 complete.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

95

Fig. 33. Acdestis oweni Ameghino, 1887, p. 5 (Santacrucian). MACN 5561 (type of
"Decastis columnaris"), a right mandibular ramus with alveoli of P 2 and M,. and P :) -M :t
complete: a, labial; b, occlusal; c, lingual views. Scale = 5 mm.

Type of Acdestis parvus. — MACN 5553, a nearly complete mandible
with left and right rami articulated; left ramus with base of I,, alveoli of
I 2 -P 2 , and P 3 -M 4 complete; right ramus of I,, alveoli of I 2 -P 2 , P»-M 2
complete, and alveoli of M :M (MACN 5554, a vertebra, and MACN
5555, a diaphysis of a humerus, are of same individual).

Type of Callomenus intervalatus. — MACN 5693, a fragment of a
right mandibular ramus with three alveoli on preserved portion of di-
astema (probably C-P 2 ), roots of P 3 , and M,. 2 present but very worn.

Lectotype of Callomenus ligatus. — MACN 8257, a left mandibular
ramus with alveoli of I,-P 2 , P 8 -M a complete (specimen matches all mea-
surements in original description perfectly, and it is the only probable
cotype with the M., as indicated in original description).

%

FIELDIANA: GEOLOGY

Fig. 34. Acdestis oweni Ameghino, 1887, p. 5 (Santacrucian). PU 15225, left maxillary
with alveoli of C and part of P 1 . and P 2 -M' complete: a, labial; b, occlusal; c, lingual
views. Scale = 5 mm.

Type of Callomenus robustus. — MACN 8260, a left mandibular
ramus with P 3 -M 2 complete (but very worn), and roots of M ;{ _ 4 (listed as
type on card with specimen but not in Ameghino's catalogue — it does,
however, fit original description perfectly).

Type of Decastis columnaris. — MACN 5561, a right mandibular
ramus with P,rM ;! complete (figured by Ameghino, 1893b, fig. 3; 1894,
fig. 32; 1898, fig. 50c; 1903, fig. 97).

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MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

99

Table 18. Statistics for some cheek tooth dimensions of Acdestis oweni.

Dimension

Upper cheek

F

L

W

M'

L

W

M 2

L

W

M 3

L

W

M 4

L

W

M' 4

L

F-M 4

L

Lower ch

IEEK

P.

L

W

M,

L

w

M,

L

W

M,

L

W

M 4

L

W

M,. 4

L

P.rM 4

L

N

OR

CV

8

2.9-3.1

3.03

0.07

2.31

8

2.0-2.4

2.20

0.13

5.91

8

3.3-3.7

3.55

0.15

4.23

8

3.2-3.4

3.33

0.07

2.10

8

2.4-2.6

2.49

0.08

3.21

8

3.0-3.2

3.14

0.07

2.23

7

1.1-1.3

1.26

0.08

6.45

7

1.8-2.0

1.%

0.08

4.08

6

0.8-1.0

0.87

0.08

9.20

6

1.2-1.3

1.28

0.04

3.13

7

8.4-8.6

8.49

0.07

0.82

6

10.5-11.1

10.87

0.24

2.21

23

0.9-1.5

1.05

0.12

11.43

23

0.8-1.2

0.95

0.10

10.53

27

4.1-4.7

4.39

0.16

3.64

28

2.0-2.4

2.12

0.12

5.66

23

2.7-3.0

2.86

0.13

4.55

24

1.8-2.3

2.03

0.13

6.40

16

1.7-1.9

1.77

0.08

4.52

16

1.3-1.7

1.50

0.10

6.67

9

0.8-1.0

0.94

0.07

7.45

9

0.9-1.0

0.98

0.04

4.08

14

10.3-12.5

10.50

0.51

4.86

11

10.3-12.5

11.37

0.64

5.63

Type ofDecastis run genus. — MACN 5562, a right mandibular ramus
with P ;t -M;, complete, and roots of M 4 (listed as type in Ameghino's
catalogue).

Type of Metriodromus spectans. — MACN 8254, a right mandibular
ramus with M :1 complete, and alveoli of rest of dentition.

Hypodigm. — The ten types and MACN 2039, a fragment of a left
mandibular ramus with M,. 2 (labeled D. spegazzinii); MACN 2040, a
fragment of a left mandibular ramus with M, (labeled D. spegazzinii);
MACN 5546, a fragment of a right mandibular ramus with alveoli of
M 2 , and M.,. 4 complete; MACN 5547, a fragment of a left mandibular
ramus with roots of P,, and P 2 -M 2 complete but worn; MACN 5548a, a
fragment of a right mandibular ramus with alveoli of I 2 -P 2 , P :1 -Mi com-
plete, and roots of M 2 ; MACN 5548b, a fragment of a right mandibular
ramus with alveoli of P. { , and M,. 2 complete but worn; MACN 5549, a
left mandibular ramus with M,. 4 ; MACN 5550, a left mandibular ramus
with P 3 -M 3 ; MACN 5551, a left mandibular ramus with M,. 4 ; MACN

100 FIELDIANA: GEOLOGY

5552, a right mandibular ramus with Fj-M, complete, aijd trigonid of
M 2 ; MACN 5556, a fragment of a right mandibular ramus with P ;5 -M,;
MACN 5557, a fragment of a left mandibular ramus with P 3 -M 2 ; MACN
5558, a fragment of a left mandibular ramus with M 2 _ 4 ; MACN 5560, a
left mandibular ramus with P ; ,-M 4 complete; MACN 5645, a right
maxillary fragment with P 2 -M 4 (labeled M. intermedius); MACN 8251,
a right mandibular ramus with P., complete, and alveoli of rest of teeth
(labeled D. rurigenus); MACN 8253, a fragment of a right mandibular
ramus with P 3 -M 2 (labeled D. rurigenus); MACN 8255, a fragment of a
left mandibular ramus with P ;r M, complete (labeled C. ligatus and a
possible cotype of that species); MACN 8256, a fragment of a right
mandibular ramus with I,, and P ;r M 2 complete (labeled C. ligatus and a
possible cotype of that species); MACN 8258a, a fragment of a left
mandibular ramus with I,-P ;! complete (possible cotype of C. ligatus);
MACN 8258b, an isolated right lower I, (figured by Ameghino, 1903,
fig. 5, and possible cotype of C. ligatus); MACN 8312, palate of skull
with right P ! -M 4 , and left P'-M ! complete [figured by Ameghino (1903,
fig. 100) asE. holmbergi] (labeled M. holmbergii); MACN 10236, a left
mandibular ramus with P 3 -M 3 complete, and roots of M 4 (labeled A.
elatus); FMNH P13160, a partial skull with right P 3 -M 4 complete, a
partial right mandibular ramus with talonid of M 2 , and all of M :! . 4 com-
plete, and a partial left mandibular ramus with P :r M 4 complete (all of a
single associated individual); AMNH 9124, a partial left mandibular
ramus with M,_ 2 complete, and an associated partial right ramus with
M,. ;{ complete, and alveoli of M 4 ; AMNH 9550, a partial left maxillary
with P-M 2 complete; AMNH 9594, a partial right mandibular ramus
with base of I,, and P 2 and M,_ 2 complete; PU 15066, a right mandibular
ramus with base of I, , alveoli of I 2 -P, , P :1 -M :) complete, and roots of M 4 ;
PU 15225, a partial skull with much of upper dentition; PU 15710, a
partial left mandibular ramus with P 3 -M 2 complete, and roots of M :5 . 4 ;
PU 15952, a fragment of a right maxillary with roots of P 1 and P 2 -M 4
complete; [I was unable to find or identify the specimen figured by
Ameghino (1903, figs. 34, 38) as Callomenus robustus, although it is
clearly referable to A. oweni]; MLP 11-50, a fragment of a left man-
dibular ramus with M 2 . 4 complete; MLP 11-72, a right mandibular
ramus with alveoli of P ;i (two rooted), M,. s complete but very worn, and
alveoli of M 4 ; MLP 1 1-73, a right mandibular ramus with roots of P,. 2 ,
P 3 complete (two rooted), alveoli of M,, and M 2 . 4 complete.

Horizon and locality. — All specimens are from the Santa Cruz For-
mation, Santa Cruz Province, Patagonia, southern Argentina, and their
localities of collection are as follows: [La] Cueva MACN 8251, 8253,

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 101

8254, 8255, 8256, 8260, 8312 (collected by C. Ameghino, 1892-93); Coy
Inlet PU 15710 (collected by O. A. Peterson, 1899); Killik Aike PU
15066 (collected by O. A. Peterson, 18%), PU 15952 (collected by O.
A. Peterson, 1899); La Costa, 2 miles west of Coy Inlet FMNH PI 3 160
(collected by J. B. Abbott, 1923-24); 5 miles South of Coy Inlet
PU15225 (collected by O. A. Peterson, IS96); Santa Cruz MACN 1379;
Rio Gallegos AMNH 9124, 9550, 9594 (collected by B. Brown, 1899);
Sehuen MACN 5553, 5645 (collected by C. Ameghino, 1890-91); Monte
Observation MACN 5546, 5547, 5548a, 5548b, 5549, 5550, 5551, 5552,
5556, 5557, 5558, 5559, 5560, 5561, 5562, 5693 (collected by C.
Ameghino, 1890-91), MACN 8257, 8258a, 8258b (collected by C.
Ameghino, 1892-93); MACN 2038, 2039, 2040 (1889-90, no other data);
MACN 10236, MLP 11-50, 11-72, 11-73 (no data).

Age . — Santacrucian.

Diagnosis. — M, and M 2 are slightly shorter than in Deseadan species
Acdestis praecursor; smallest P :{ relative to M, of all known Santacru-
cian Palaeothentinae.

Description. — Two partial skulls of Acdestis oweni are known — PU
15225 and FMNH 13160. The former was described and figured by
Sinclair (1906, pp. 427-428, pi. 63, fig. 3, pi. 64, figs. 1, la) as
Palaeothentes intermedius.

The braincase is large, bulbous, and widely expanded posteriorly.
There are no postorbital processes, but the weak temporal ridges con-
verge posteriorly to form a low sagittal crest. Between the anterior
edge of the orbits, the frontals form a broad flat plane. The frontals
have a broad sutural contact with the maxillaries at a point dorso-
anterior to the anterior edge of the orbit.

The nasals are broad and pointed posteriorly, and they decrease
rapidly in width anteriorly. Unlike known fossil (i.e., Pichipilus) and all
living Caenolestinae, there is no trace of an antorbital vacuity between
the nasal, maxillary, and frontal. The premaxillaries resemble those of
living Caenolestinae in having a narrow extension between the maxil-
lary and nasal (see Sinclair, 1906, pi. 63, figs. 3, 14, pi. 64, fig. la). The
lacrimal is largely confined to the orbit with only a small facial contri-
bution along the anterodorsal edge. The lacrimal duct opens within the
rim of the orbit and supports a small but distinct lacrimal tubercle. A
large infraorbital canal opens above the anterior root of the P 3 .

The anterior margin of the orbit is well defined and is modified into a
sharp rim. The jugal extends posteriorly and forms the anterior edge of
the glenoid fossa. The squamosal portion of the zygomatic arch is not

102 FIELDIANA: GEOLOGY

inflated as it is in some Australian phalangeroids (e.g., Petaurus). The
alisphenoid is slightly inflated and forms an ossified contribution to the
auditory bulla anteriorly.

The palate is deeply concave anteroposteriorly and transversely and
is perforated by two large anteroposteriorly elongated palatal vacuities.
The latter extend from a point opposite the anterior extremity of M 1 to
a point posterior to M 4 . Small nutrient canals perforate the bony por-
tion of the palate. The palatal-narial border is thickened, ridge-like, and
elevated to a height equal to that of the occlusal surfaces of M 14 .

Comments. — A marked amount of variation occurs in the size and
the number of antemolar teeth in Acdestis oweni. In all specimens
except MACN 8260,* the P. { is very small relative to the M,. In MACN
1379, 5553, 5559 (fig. 32), 5562, 5693, 8257, and PU 15066 the P, is
clearly double rooted; in MACN 2038 it appears to be single rooted
(although it may be incipiently double rooted and have a figure 8-
shaped root); in MACN 8254 it appears to be single rooted as evi-
denced by the figure 8-shaped alveolus, with the anterior part being
smaller than the posterior (a double root with a single alveolus is
suggested); and in MACN 5561 (fig. 33) it is definitely single rooted.
When double rooted, the posterior root is always larger than the an-
terior root.

The diastema is complete in MACN 1379, 5553, 5559, 8254, 8257,
and PU 15066. In the former three specimens there are four tiny,
single-rooted teeth (I 2 , C, P,, P 2 ) or their alveoli on the diastema an-
terior to the P :! , and in all cases the last (P 2 ) is the smallest, and in
MACN 5553 (and MACN 5562) its alveolus is confluent with the an-
terior alveolus of the P 3 . In the latter three specimens there are only
three tiny alveoli anterior to the P ;i (probably I 2 , C, P,), and it appears
that the one just anterior to the P ;1 (the P 2 ) was lost. In MACN 5693 a
small diastema occurs just anterior to the P ti , which is then followed by
three tiny teeth (presumably P, , C, I,) — this space presumably marks
the site of a former fourth tooth (the P 2 ), whereas in MACN 8254 there
is a tiny lingual depression between the P, alveolus and that anterior to
it (the P,?) that could represent the remnant alveolus of the missing P 2 .
In MACN 2038, 5561, and 8260 there are three rudimentary teeth on
the diastema, but the anterior ends of these diastemas are broken away
and with it may have been lost a fourth rudimentary tooth (the I 2 ).

*In MACN 8260 the P., is double rooted and is somewhat larger (table 17) than in other
specimens. It is reminiscent of specimens of the slightly larger Palaeothentes lemoinei,
although in that species the P :t is much larger (compare specimens in fig. 17). In length of
M,. 4) MACN 8260 falls within the range of other specimens assigned to A. oweni (table
17), and it is smaller than those assigned to P. lemoinei (table 13).

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 103

The Deseadan Acdestis praecursor and the Santacrucian A. oweni
are the only species of Acdestis known. Their only real difference is in
the slightly larger size of the lower molars in A. praecursor. It is possi-
ble to envision A. praecursor as the Deseadan ancestor of A. oweni if a
slight diminution in size occurred in this lineage. Alternatively, these
species may represent independent derivations from a common pre-
Deseadan ancestor. I favor the first view as there is no conflicting
evidence against such a lineage relationship.

Palaeothentinae — Indeterminate

I was unable to locate the types of two of Ameghino's 1887 species of
Palaeothentes, P. pachygnathus and P. pressiforatus. As a result I am
neither able to determine their validity nor their systematic position
with regard to the other named species. Both species were erected on
specimens collected by Carlos Ameghino from the Santa Cruz Forma-
tion of Patagonia. The types should be in the MLP although neither
could be located in the collections of that institution. A catalogue card
in the MLP for specimen 1 1-32 bears the name of one of these species
(P. pachygnathus), although neither I nor Rosendo Pascual could lo-
cate the specimen. Several possibilities regarding the fate of these
types exist: (1) they are lost; (2) they are temporarily misplaced; (3)
they are among known MLP specimens but are not recognized as the
types; or (4) they were taken by Ameghino to the MACN and are now
in the Ameghino Collection of that institution (see footnote, p. 36).
Whatever the case, I here regard these species as nomina vana.

The original descriptions and pertinent literature citations for these
species follow:

1. Palaeothentes pachygnatus sp. n. — Talla todavia menor, pero relativamente mas
robusto (than P. lemoinei). — Parte sinfisaria de la mandibula, muy espesa. — Cara
externa de la rama horizontal debajo del pm M , muy convexa. — Largo del pm. 4
4mm. — Largo del pm. : , pm. 4 y m., — 0.0095. — Alto de la rama horizontal debajo del
pm. 4 , 6 mm. (Ameghino. 1887, p. 6).

Palaeothentes pachygnatus* [sic] Ameghino, 1887, p. 6.

Epanorthus pachygnatus* [sic] Ameghino, 1889, p. 273; 1894, p. 347; 1898, p. 186.

Palaeothentes pachygnathus Sinclair, 1906, p. 454; Simpson, 1930, p. 58.
2. Palaeothentes pressiforatus, sp. n. — Tamano mas considerable que el de la
especie precedente (P. intermedius), comparable al del Palaeothentes Lemoinei. —
Los dos agujeros mentonianos de cada rama mandibular, muy proximos entre si, el
anterior debajo de la parte posterior del pm. 2 , y el posterior debajo de la segunda raiz
del pm.;„ a solo 3 mm. de distancia. — Alto de la rama horizontal debajo del pm. :1 , 6
mm. (Ameghino, 1887, p. 6).

*Despite the fact that Ameghino repeatedly spelled the trivial name pachygnatus
this seems such an obvious lapsus calami that it seems permissible to accept the
corrected form [pachygnathus] (Simpson, 1930, p. 58).

104 FIELDIANA: GEOLOGY

Palaeothentes pressiforatus Ameghino, 1887, p. 6. *

Epanorthus pressiforatus Ameghino, 1889, p. 274; 1894, p. 347; 1898, p. 186.

Palaeothentinae — Unidentified

In the summer of 1976, I visited the British Museum (Natural His-
tory), London, and made a brief survey of south American fossil mar-
supials in the collection of that institution. Nine specimens were
labeled Epanorthus sp. and are clearly referable to the subfamily
Palaeothentinae. I did not then study these specimens in any detail nor
have I had the opportunity to do so for this present review. I list these
specimens here for the sake of completeness — BM(NH) M5685, 5686,
5687, 5688 (all presented by F. Ameghino in 1895); 7267, 7326 (both
purchased from R. Damon in 1899); 11724, 11725, 11726 (collection of
W. E. Balston purchased by J. R. Gregory & Co., August, 1919).

Other known specimens of palaeothentines not seen by me include:
AMNH 9592, a partial left mandibular ramus with P ;5 and M 3 . 4 (col-
lected by B. Brown from the Rio Gallegos in 1899); PU 15072, a frag-
ment of a maxillary (collected by J. B. Hatcher and O. A. Peterson in
1897 from the Rio Chalia, 30 miles east of the Cordillera); PU 15513,
upper teeth (collected by O. A. Peterson in 1899 from Coy Inlet); and
PU 15559, an edentulous left lower jaw (no collection data). All of the
above specimens are from the Santa Cruz Formation of Patagonia.

Tournouer (1903, p. 469) reported "un Epanorthus" from beds of
Deseadan age at La Flecha on the south side of the mouth of the Rio
Deseado, and specimens of Abde rites meridionalis, Epanorthus, and
Garzonia from beds of Santacrucian age at Monte Leon. These speci-
mens are in the MNHN and have neither been described nor figured.

Summary of Evolution of Palaeothentinae

Members of subfamily Palaeothentinae are known from beds of De-
seadan through Santacrucian age in Patagonia, southern Argentina,
and in beds of Deseadan age in Bolivia. Two genera, Palaeothentes and
Acdestis, are recognized.

Palaeothentes is the most generalized of the two, and it most closely
approximates the basal stock for the subfamily and in turn the ancestor
of Caenolestini. Species of Palaeothentes are distinguished from those
of Acdestis in their possession of a large two-rooted P. ? that is greater
than Vi the height of the M, ; in a relatively longer, less crowded di-
astema; and in the presence of a bifurcated paraconid on the M,. In the
latter feature, the paraconid region branches into two small crests. One
extends lingually perpendicular to the main axis of the tooth. A second
crest extends anteriorly, linking the protoconid-paraconid shear crest

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 105

of the M, trigonid with the cutting edge of the large P :{ . This crest
furnishes continuation of the shearing surface between the P. { and the
protoconid-paraconid crest of the M, (figs. 16, 17).

The smallest and most generalized of the known species of
Palaeothentes (and of the Palaeothentinae) is P. minutus. This species
retains several features found only in ancestral Caenolestini (e.g., an
"intermediate conule" on unworn upper molars and a two-rooted P 2 in
some specimens), and it serves as a proto- or morphotype from which
may be derived all other known species of Palaeothentinae and for that
matter Abderitinae.

The next largest species isf\ intermedius. It has slightly larger linear
molar dimensions and a relatively larger P. { than the Colhuehuapian
species P. primus, but these differences are minor, and the two species
appear to represent a single phylogenetic lineage. I therefore recognize
P. primus as the Colhuehuapian ancestor off. intermedius.

The Deseadan species P. lucina is of medium-large size and differs
from the Santacrucian species P. lemoinei in being slightly smaller in
overall linear tooth dimensions but in having an absolutely larger P. { .
These species also appear to form a phylogenetic lineage, and the
former is here regarded as representing the Deseadan ancestor of the
latter.

Palaeothentes boliviensis is of large size and is known only from a
single specimen from the Deseadan Salla fauna of Bolivia. It does not
appear to be related ancestrally to any known later species. Based on
its large size and its high, broad P :J , P. boliviensis shows closer affinities
to the Deseadan species P. chubutensis than to any other known De-
seadan palaeothentine. This suggests that these species shared a com-
mon ancestor more recent than those shared with other Palaeothen-
tinae.

The Deseadan species P. chubutensis and the Santacrucian P. aratae
are the two largest species of Palaeothentinae (and Caenolestidae)
known. The former differs from the latter in having a slightly deeper,
more robust mandibular ramus and a slightly larger P :! , but these dif-
ferences are minor and their range of variation within each species is
not yet known. There is little problem in regarding P. chubutensis as
the Deseadan ancestor of P. aratae. Palaeothentes aratae further dif-
fers from other palaeothentines in having a single-rooted P 1 . This state
may have existed in the ancestral P. chubutensis, but the upper denti-
tion of that species is not yet known.

Species of Acdestis share a number of apomorphous states not found
in species of Palaeothentes. The jaw and especially the diastema in

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MARSHALL: SYSTEMATICS OF CAENOLESTIDAE

107

Fig. 35. Dendrogram showing probable phylogenetic relationships of the genera and
species of Palaeothentinae. Only relative positions of pre-Deseadan common ancestors
are indicated.

Acdestis is foreshortened, resulting in a crowding of the antemolar
teeth. A consequence of this is loss in some specimens of the P 2 and in
a significant reduction in size of the P :{ . The P. { is less than Vz the height
of the M, trigonid in all specimens; it may be single or double rooted,
and it tends to be tucked under the anterior edge of the M, trigonid. The
M, becomes relatively larger than the other cheek teeth, it is the most
pronounced of the cheek teeth, and the size decrease from Ml to M4 is
sharper than in species of Palaeothentes. The paraconid on the M, is
not bifurcated as in species of Palaeothentes, an important feature for
distinguishing isolated M,'s of such similar-sized contemporary species
as Acdestis oweni and Palaeothentes intermedius. In the upper molars,
the stylar area is swollen especially labial to the M 2 paracone and also,
but less so, labial to the M 1 and M 2 metacone.

108 FIELDIANA: GEOLOGY

Two species of Acdestis are recognized, the Deseadan A. praecursor
and the Santacrucian A. oweni. Acdestis praecursor differs from A.
oweni only in the M, and M 2 being slightly longer. In other respects
these species are inseparable. I regard them as representing a single
evolutionary lineage and recognize A. praecursor as the slightly larger
Deseadan ancestor of A. oweni.

Some diagnostic characters for the species of Palaeothentinae are
listed and compared in Table 19. The character states that occur in
Palaeothentes are regarded as plesiomorphic, those in Acdestis, as
apomorphic. The probable phylogenetic relationships of the two genera
and 10 species are shown in Figure 35. This suggested phylogeny is
based on the data set in Table 19, and for want of better characters I
have regarded size increase as an important apomorphy in several
instances.

PHYLOGENETIC SYSTEMATICS
Methodology

Cladistic analysis is a procedure for inferring phylogeny as branching
sequences in evolutionary time. Extensive discussions of this method
are given by Hennig (1966), Brundin (1966, 1968), Kavanaugh (1972),
Ashlock (1974), and Andersen (1978). The fundamental premise of
cladistics is that relatedness is demonstrated by shared, derived
(synapomorphous) character states, not by shared primitive
(symplesiomorphous) ones. The methods used here for determining if a
character is plesiomorphic (primitive), symplesiomorphic (primitive
and possessed by more than one species), apomorphic (derived), or
synapomorphic (derived and possessed by more than one species)
largely conform with those of Schaeffer et al. (1972). Use of such terms
as sister-group, monophyly, morphocline, polarity, character state,
convergent evolution, and parallel evolution follow the definitions of
Hecht (1976), Hecht & Edwards (1976), and Kirsch (1977a).

Establishment of polarity is therefore the most important problem in
the analysis of a morphocline or transformation series. The parts of
these sequences must be evolutionary homologues. For a series of
comparisons there can be only one primitive state, and criteria for
determining the primitive state must be rigidly followed.

One method for determining whether a character is primitive or de-
rived for a particular taxon is by application of the principle of com-
monality (Schaeffer et al., 1972). If a character or suite of characters is
found in the majority or in all members of the group under considera-
tion, it is concluded that the character was present in the common
ancestor of that group and was not independently derived in each in-
stance of its occurrence. The unique origin of this character state is the
most parsimonious explanation for its distribution, and the cladogram
requiring the fewest steps or changes is preferred (Hecht, 1976, p. 340;
Ashlock, 1974, p. 83). Any variation from the inferred primitive state is
regarded as a derived state.

109

110 FIELDIANA: GEOLOGY

Doubts have been expressed concerning the validity of the "com-
mon is primitive" postulate, and contentions that a rare state is primi-
tive may involve appeals to character state distribution in a wider range
of taxa of different levels of cladistic relatedness. This fact leads to a
second method for establishing plesiomorphy, out-group comparison.
For this, a minimum of three groups must be used — the two or more
taxa under consideration and an out-group consisting of some other
taxon or taxa hypothesized to be related to these two. If a character or
suite of characters is found to be unique to one of the two taxa not in
the out-group, two possibilities must be considered: (1) the character(s)
evolved from a simpler, more primitive condition in only one of the
groups; or (2) the character(s) was present in the common ancestor, but
was secondarily lost in one of the two groups. Decisions concerning
these choices can be made following comparisons with one or more
out-groups (Reig et al., In prep.).

Decisions about the relative plesiomorphy or apomorphy of charac-
ter states may also be tempered by knowledge of what sorts of changes
are possible for a given character. For example, improbable polarities,
such as the resurrection of complex structures from lost or reduced
states, can be given low probability of occurrence (Hecht, 1976, p.
341).

Once the primitive state of a character has been inferred, the
apomorphous states may be ordered corresponding to the likely evolu-
tionary sequence and this series used to infer the relationships of the
taxa in which those states co-occur. The transformation of a sequence
may be simply linear and be expressed as in the stepwise four-
character state morphocline a— >b— »c— »d, or it may be complexly
branching. These alternatives can only be determined empirically by
sequential comparison of the cladograms suggested by each series of
character states. The degree of concordance or discordance between
characters suggests the extent of convergence or parallelism in those
characters. Ordinarily, one begins an analysis with three or four taxa
likely to be closely related and determines their cladistic relatedness by
means of the best-established character morphoclines. All types of
branching patterns should be examined, and the simplest pattern may
not necessarily be the correct one for any given character. Clearly, for
more than a few characters, the number of possible cladograms is very
large, particularly when some character-sequences do not give con-
cordant cladograms due to convergence, to parallelism, or to mistaken
homologies. The greater the concordance between different clado-
grams, the more likelihood that the original hypothesis of relatedness
was correct (Hecht, 1976, p. 341; Reig et al., In prep).

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 1 1 1

Character Analysis

Discussions of the phylogenetic relationships of caenolestid sub-
families have been based on an array of characters that have not pre-
viously been analyzed in a cladistic framework. An attempt is made to
treat all useful or potentially useful characters for which data are avail-
able. The analysis for each character is presented in an abbreviated
form, with extensive literature citations to more detailed coverage.

Two basic groups of characters may be recognized. Hard part fea-
tures, like bones and teeth, are based on an analysis of both living and
fossil forms, employing both the principle of commonality and out-
group comparison. Inference of the distribution of soft part features is
based largely on the application of the principle of commonality. It is
assumed, with reservations but in the absence of conflicting (or any)
data, that the states of soft part features in living Caenolestini are the
same in all fossil Caenolestidae.

I have selected 12 characters for analysis and have arranged them in
the general order of head, dentition, and postcranial. Most of the
characters are unique and distinct, but others represent "complexes"
that I have attempted to isolate into component parts.

An analysis of each of these characters follows.

1 . Antorbital vacuity. — An antorbital vacuity, bounded by the nasal,
frontal, and maxillary occurs on each side of the face directly above the
infraorbital foramen in all living Caenolestini (see Osgood, 1924, pi. 23)
and in a fossil species of Pichipilini, Pichipilus centinelus (see Marshall
& Pascual, 1977, p. 104, fig. 4). As seen in living species, this vacuity
opens into the large sinus between the nasoturbinal and the maxillary.
Its relations to the overlying dermal tissues are simple, and no glandu-
lar or other special development is apparent (Osgood, 1921, p. 107).

A vacuity of this type does not occur in the two known skulls of the
palaeothentine Acdestis oweni (see p. 101) nor in any other known
marsupial group. Among placentals, a vacuity in this part of the skull is
found only among ungulates (Osgood, 1921, p. 107). Among Mar-
supialia in general and Caenolestidae in particular, an antorbital va-
cuity is regarded as an apomorphy for the subfamily Caenolestinae,
since it occurs in all known skulls in members of both recognized
tribes.

2. Palatal vacuities. — The palate in marsupials is often perforated by
three sets of palatal vacuities or fenestrae adjacent to the palatal mid-
line. Because of the widespread occurrence of these vacuities in mar-
supials, their presence is generally regarded (e.g., Tyndale-Biscoe,
1973) as plesiomorphous for the group.

112 FIELDIANA: GEOLOGY

Large palatal vacuities occur in all living Caenolestini (see Osgood,
1924), in the fossil Pichipilus centinelus (see Marshall & Pascual, 1977,
p. 104), and in the two known skulls of the palaeothentine Acdestis
oweni (see p. 102). Based on the traditional view, the presence' of
palatal vacuities in caenolestids would thus be regarded as a retained
primitive marsupial character.

Elsewhere, I reviewed the distribution of palatal vacuities in marsu-
pials in particular (1977, p. 415) and in mammals in general (1979b, p.
377). In the former study I was led to conclude that palatal vacuities
may have evolved independently in various marsupial lineages. In the
latter study I concluded that a solid, unfenestrated palate was
plesiomorphic for mammals in general and prototherians, therians,
metatherians, and eutherians in particular.

The relevant point for this study is that all known caenolestids have a
fenestrated palate and that nothing can be said about the inter-
relationships of caenolestid taxa based on this character. At the family
level, the occurrence of a fenestrated palate can be regarded as a
plesiomorphic feature.

3. Brain. — All marsupial groups, except for Australasian di-
protodonts (= Phalange roidea sensu Ride, 1962, p. 301), show the same
pattern of commissural connections as do monotremes, and this ar-
rangement probably also occurred in the common therian ancestor of
marsupials and placentals. In this basic arrangement there are two
large fiber bundles interconnecting pallial structures of the two cerebral
hemispheres, the dorsal or hippocampal commissure and the ventral or
anterior commissure.

In Australasian diprotodonts a third bundle of neocortical commis-
sural fibers is added, the fasciculus aberrans. Ride (1962, p. 301), fol-
lowing Abbie (1939), used the term duplicicommis sural for the pres-
ence of a fasciculus aberrans in the forebrain and simplicicommisural
for the lack of this structure. The former condition is regarded as
apomorphic for Phalangeroidea and the latter condition as plesiomor-
phic (for review of pertinent literature on this point see Marshall,
1979b, p. 374).

The brains of Caenolestes and Lestoros were studied by Obenchain
(1925), and they lack a fasciculus aberrans (Abbie, 1937, 1939). They
are therefore plesiomorphic for this feature.

4. Dental formula. — The most generalized of living marsupials, the
American Didelphidae, have a dental formula of It, CJ, P;|, M4. This is
the highest number of teeth known for any fossil or living marsupial,
and all specializations involving reduction in other marsupial groups

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 113

may be derived from this formula. This formula is regarded as
plesiomorphic for Marsupialia (Marshall, 1979b, p. 388).

Many attempts have been made to identify homologous teeth in mar-
supials and placentals, and this has resulted in a plethora of symbolic
and ordering systems, and in conflicting dental terminology. The issue
is still debated, and no one system has yet been agreed upon. The most
recent attempt to stabilize this issue is that of Archer (1978).

It is not my intention to enter this debate by accepting one con-
troversial system over any other. I therefore use the following con-
ventional system for serial designation of the teeth in the Marsupialia;
for the incisors and canine it is intended to be descriptive and does not
imply homology although for the premolars and molars homology is
implied: I{ \ \ \ 5 , C{, PJ | §, M} 1 § t Any deviation from this formula is
regarded as a derived condition.

Attempts to establish homologies of the antemolar {sensu Ride, 1962,
p. 297) dentition between caenolestids and didelphoids are given by
Osgood (1921, p. 112) and Ride (1962, p. 297). The homologies of the
upper incisors and of the lower antemolar teeth of caenolestids are
difficult to establish because nothing is yet known of the dental em-
bryology of this group. Attempts to establish homology have thus been
based on study of adult specimens, living and fossil.

Individuals of Caenolestes have as many as eight antemolar teeth
(Bensley, 1903, p. 124, pi. 5, fig. 38; Osgood, 1921, p. 112) and thus
retain the plesiomorphic number for Marsupialia. A specimen of
Stilotherium dissimile ("Garzonia") is reported by Sinclair (1906, p.
417) to have nine lower antemolar teeth. Ride (1962, p. 298) has opted
to regard this number as an individual peculiarity, pending confirma-
tion of the consistency of its occurrence. If, however, this number is
not aberrant, the lower dental formula may be 15, CI, P3, M4, since the
maximum number of premolars in any known didelphoid is three, and
the canine is always single (ibid.). This would indicate that the lower
incisor number in caenolestids was either increased from 4 to 5 and the
condition should be regarded as an apomorphy, or that the primitive
marsupial number was 5. The latter possibility has been discussed in
more detail by Ride (1962).

Archer (1978, p. 163) studied over 150 specimens of the three living
genera of Caenolestinae and found no evidence of a milk tooth or of
tooth replacement of any sort. In addition, there is no evidence for
tooth replacement in any fossil caenolestid. Archer (ibid.) concluded:

If tooth replacement of the sort which occurs in other marsupial orders does occur in

caenolestoids, it must occur very early in ontogenetic development. ... If tooth

1 14 FIELDIANA: GEOLOGY

replacement does not occur, then it is possible that caenolestoids represent a unique
order of marsupials all members of which have no more than seven postcanine cheek
teeth.

The apparent loss of this tooth in caenolestids is thus regarded as <an
apomorphic feature for members of this family. It is tempting to
speculate that the extra antemolar tooth in the specimen of
Stilotherium discussed above represents the retained deciduous tooth.
The least number of lower incisors possessed by Stilotherium is four,
and in Caenolestes it is three. Assuming caenolestids have the same
number of tooth germs as other marsupials, the lower procumbent
incisor is almost certainly developed from the first incisor germ, or the
I,, by homology with didelphoids (Ride, 1962, p. 298).

The plesiomorphic incisor formula for the Caenolestidae is here
taken to be 4. Reduction to | in some Caenolestinae and to i in
Palaeothentinae and presumably this (or a lower) number in Ab-
deritinae are considered apomorphous states. Likewise, the presence
of only two lower premolars in some specimens of Acdestis oweni is
regarded as derived from the higher condition of three. In this case, the
reduction apparently involves loss of the P 2 (see p. 102). The following
serial designations are used for the various subfamilies of Caenoles-
tidae (parentheses indicate absence of teeth in some included taxa or
individuals):

Caenolestidae

ii 2 34

M 2 (3 4)

CJ

pi 2 3
r l 2 (3)

Vf 1 2 3 4

ivl l 2 3 4

Caenolestinae

Tl 2 3 4
x l 2 3 (4)

C]

pi 2 3
r 1 2 3

Vfl 2 3 4
ivl l 2 3 4

Abderitinae

M 2

Ci

P, Is

Vf 1 2 3 4

XV1 1 2 3 4

Palaeothentinae

11 230
L l 2

Cj

PI 2 3

r l 2 (3)

Vfl 2 3 4

ivl l 2 3 4

5. Dental specializations. — In late Cretaceous members of the Di-
delphidae (see Clemens, 1966) and in most living forms (see Reig et al.,
In prep.), the incisors are unspecialized and are similar in size; the
premolars are well developed, trenchant, and double rooted; and the
molars are well developed and tuberculo-sectorial in structure. The M4
is subequal in size to the M3, and a well-developed stylar shelf with
distinct cusps is present on the upper molars. This type of tooth struc-
ture is regarded as plesiomorphic for the Marsupialia (Archer, 1976).

Derived states for the family Caenolestidae include development of a
hypocone (this term is used without implication of homology) on M 1 " 3 ;
increase in size and development of a procumbent, lanceolate, di-
protodont I,; reduction in size of most other antemolar teeth; presence
in unworn teeth of a small but high and distinct "intermediate conule"
(sensu Osgood, 1921, p. 120) at the inner base of the metacone on M 1 * 3 ;

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 1 15

and the reduction in size of the M4. Further specializations within the
family are discussed on p. 23.

6. Teat number. — Within the Marsupialia, the number and distribu-
tion of teats vary greatly. In the South American didelphoid Monodel-
phis, up to 27 teats are distributed over the inguinal, abdominal, and
pectoral areas (Thomas, 1888; Reig et al., In prep.; Thomas, 1888,
figured a specimen of Monodelphis henseli with 25 teats, but mentioned
one in the text that had 27). The lowest number occurs in species of
Notoryctes, Distoechurus, Phascolarctos, and Vombatus that have
two teats (Osgood, 1921, p. 75).

The primitive teat number for Marsupialia is believed by Bresslau
(1912, 1920) to be 25, and he concluded that all specializations involve a
reduction in this number. Of the 26 genera listed by Osgood (1921), four
had two teats, 10 had four, and the remaining 12 had a number higher
than seven. In Caenolestes there are four mammae — two on each side
of the abdomen inside the thighs (Osgood, 1921, p. 75); Lestoros has
four mammae (Collins, 1973, p. 173); and Rhyncholestes has five
mammae — two inguinal on each side and one midventral slightly in
advance of them (Osgood, 1924, p. 169). The low teat number in living
Caenolestinae is thus regarded as a derived state.

7. Pouch or "marsupium." — Elsewhere, I (1979b, p. 383) reviewed
information on the distribution and degree of development of a pouch
or marsupium in mammals. Based on that study I concluded, as some
others before me, that it is probable that the earliest marsupials, and
the immediate ancestors of marsupials and placentals, did not have a
pouch. Thus, a pouch apparently developed independently in various
marsupial lineages and in the echidna as an adaptation for special me-
chanical and/or locomotory needs.

There is some disagreement about the occurrence of a pouch in living
caenolestines. Tomes (1860, p. 213) wrote that his specimen of
"Hyracodon" (=Caenolestes) fuliginosus (as he later designated it)
possessed "... a small and rudimentary pouch . . .," a feature that
has not been remarked on by subsequent workers even though lactat-
ing females have been examined (Osgood, 1921, p. 21; Kirsch & Wal-
ler, 1979, p. 394). The measurements given in Tomes' (1863) descrip-
tion clearly indicate that the type specimen is a juvenile (Kirsch &
Waller, 1979, p. 394). This has caused Osgood (1921) and Kirsch &
Waller (1979) to suggest that the pouch may be a juvenile feature in
caenolestids. In any event, it can only be concluded that a pouch is not
developed in adult female caenolestids, a condition regarded as
plesiomorphic for the Marsupialia. The state of this character is, of

116 FIELDIANA: GEOLOGY

course, unknown in the fossil subfamilies Palaeothentinae and Ab-
deritinae.

8. Epipubic bones. — Ossified epipubic (=prepubic or "marsupial")
bones are present in both sexes of monotremes, in tritylodont therap-
sids, in Cretaceous multituberculates, and possibly in triconodonts and
pantotheres. They are absent in placentals. Epipubic bones are present
in both sexes of living marsupials, except Notoryctes and Thylacinus in
which they are cartilaginous and vestigial, and in South American
borhyaenids in which they are apparently altogether absent (Marshall,
1977, p. 419; 1979b, p. 385, and references therein). The presence of
large ossified epipubic bones in living caenolestines (a complete pelvis
is not known in fossil taxa) thus represents a retained primitive mam-
malian feature for the group.

9. Sperm pairing. — The phenomenon in which two sperm are united
by juxtaposition of the shorter portions of the two heads was first
observed in Didelphis marsupialis by Selenka (1887), who referred to
them as "copulating" spermatoza. This term was subsequently used
by Korph (1902), who made the crucial observation that the "copula-
tion" occurs only after the gametes reach the epididymes. Wilson
(1928) objected to the term "copulating," and instead introduced the
term "conjugating." Biggers & DeLamater (1965, p. 403) noted, how-
ever, that the term "conjugating" has acquired a specific meaning in
biology with reference to the union of gametes in unicellular organisms.
For this reason these authors, and those subsequent to them, preferred
the simple descriptive word "pairing" to describe this phenomenon.

Biggers & Creed (1962) noted that pairing of spermatozoa is a normal
occurrence in the epididymes of the North American opossum, Di-
delphis virginiana. Subsequent work by Biggers & DeLamater (1965)
has shown that pairing occurs in the epididymes of all species of
American marsupials investigated; both in members of the Didelphidae
{Didelphis, Philander, Chironectes, Monodelphis, Metachirus, Mar-
mosa, and Caluromys), and in Caenolestidae (Caenolestes) (see Big-
gers & DeLamater, 1965, p. 403, Table 1). The sperm remained paired
in the vaginae of females after copulation (Tyndale-Biscoe, 1973, p.
15), suggesting that the bond between them is quite firm. In no instance
was pairing observed in sections of the testes, indicating, once again,
that the pairing takes place in the epididymes.

Biggers & DeLamater (1965) presented data indicating the incidence
of pairing within species. Out of 92 specimens of Didelphis mar-
supialis, 88 (95.7%) had sperm that were paired, and out of 56 speci-
mens of Philander opossum, 54 (96.5%) had sperm that were paired.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 117

The fact that sperm pairing has been observed in all species (but not
every individual) of American marsupials examined, including two
families, indicates that these marsupials are derived from a common
ancestral stock that had already evolved the pairing phenomenon.
Thus, pairing of spermatozoa, whatever its function, must have be-
come established early in the evolutionary history of the American
group of marsupials (Biggers & DeLamater, 1965, p. 404).

The pairing of spermatozoa in the epididymes or in sections of the
testes has not been observed in any species of Australasian marsupials
yet investigated. These include species of Sminthopsis, Neophas-
cogale, Antechinus, Acrobates, Eudromicia, Trichosurus, Vombatus,
Perameles, Peroryctes, Wallabia, Megaleia, and Macropus (Biggers &
DeLamater, 1965, p. 403, table 2).

Because pairing of spermatozoa is not known in any eutherian
(Tyndale-Biscoe, 1973, p. 16), nor in any Australasian marsupial, it
would appear that non-pairing represents the primitive condition; the
pairing phenomenon as occurs in the American marsupials is derived.*

10. Sperm morphology. — Three distinct morphological types of
spermatozoa have been observed in American marsupials. The first
type, described by Biggers & Creed (1962), occurs in species of Di-
delphis, Monodelphis, Philander, Metachirus, Chironectes, and Mar-
moset (Biggers & DeLamater, 1965, p. 403, fig. 1). A second morphol-
ogy was found only in Caluromys, in which the spermatozoa possess
saucer-shaped heads with the mid-piece inserted into the convex side,
and the acrosome lying in the concave side. Pairing occurs by apposi-
tion of the two concave sides (Biggers & DeLamater, 1965, p. 403, fig.
2). The third type was observed in Caenolestes, in which the sper-
matozoa are very rectilinear in shape with a niche on one side from
which the mid-piece arises. Pairing occurs by apposition of the edges
opposite the insertion of the mid-piece (Biggers & DeLamater, 1965, p.
403, fig. 3).

The spermatozoa of each of five Australasian marsupial families
(Macropodidae, Phalangeridae, Dasyuridae, Peramelidae, and Phas-
colarctidae) were investigated by Hughes (1965). The morphologies of

*I must caution that this conclusion is based on a variable character, and cladists have
been notoriously unable to deal with the problem of variations of this type. An alternative
interpretation to this conclusion is that the marsupial(s) that entered Australia, probably,
via a sweepstakes route, could have been an individual(s) that by chance did not have
pairing sperm. Thus, the founder effect could be used to favor the view that Australasian
marsupials were derived from ancestors in which pairing sperm was present at some
frequency. I think this possibility is unlikely, but it does warrant consideration.

118 FIELDIANA: GEOLOGY

the spermatozoa (including dimensions of the head, flagellum, and fine
structure) of members of each family were distinct from those of other
families. In the wombat, Vombatus ursinus, and the koala, Phas-
colarctos cinereus, the morphology of the sperm, particularly of the
heads, differs strikingly from that of any other marsupial sperm de-
scribed. In both species, the proximal portion of the sperm head bears
a strongly recurved hook not described for other marsupial sperm, and
the flagellum is inserted into a notch on one side of the distal portion of
the head (Hughes, 1965, p. 541, pi. 1, fig. 1; figs, la, b). The position of
the hook in Vombatus is not an artifact of fixation, because it was
observed in living spermatozoa from the epididymes of several speci-
mens (ibid.).

Study of marsupial sperm morphology thus indicates that no special
similarity exists between any American and any Australasian groups.
Further, the sperm morphology of Caenolestes is distinct from that of
members of the family Didelphidae. Unfortunately, the ancestral state
of marsupial sperm morphology cannot yet be inferred on the basis of
available data.

11. Karyotype. — Several authors have discussed the question of the
original marsupial karyotype, and it is now generally agreed that a
diploid number of 14 is primitive for metatherians (Reig et al., 1977;
Reig et al., In prep.). The latter authors based their conclusions on a
cladistic analysis of all available data. The karyotype is known in four
species of two caenolestid genera, Caenolestes and Lestoros, and in all
the diploid number is 2n = 14 (Hayman et al., 1971; Kirsch, 1977c).
Thus, caenolestids are plesiomorphic in chromosome number.

12. Structure of pes. — In the pes of living and fossil American mar-
supials and Australasian Dasyuroidea (sensu Ride, 1962, p. 301), digits
three and four are commonly subequal, are slightly larger than digits
two and five, and are quite separate from the latter. This type of pes has
been termed didactyly (Gr. di-, prefix meaning two or double;
-daktylos, a finger or toe) and eleutherodactyly (Gr. eleutheros-, free or
not bound) and is regarded by most workers (e.g., Ride, 1962) as the
plesiomorphic state for marsupials.

In sharp contrast, the Australasian groups Perameloidea and
Phalange roidea (sensu, Ride, 1962, p. 301) have digits two and three
reduced in size relative to digits four and five, and digits two and three
are enclosed basally in a common skin sheath. In some species and
groups these digits are bound together for the whole of their length with
exception of their distal joints and claws. Digits two and three are
generally slender and are markedly shorter than digit four, the domi-

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 1 19

nant toe in the hind foot. This condition has been termed syndactyly
(Gr. syn-, together).

Some authors (e.g., Kirsch, 1977a, fig. 20) have noted that some
American didelphids show an approach to the syndactylous condition
seen in Australasian groups. However, in those didelphids having rela-
tively reduced digits two and three, these toes are not enclosed in a
skin sheath. The "true" syndactylous condition thus occurs among
marsupials only in the Australasian groups and is the apomorphic state
for this feature.

As described by Osgood (1921), Boas (1933), Lonnberg (1921, p. 76,
pi. 1, fig. 4), and Thomas (1895a, b), the pes of Caenolestes is relatively
long, narrow, and didactylous. The hallux is short, is set at a slight
angle to the rest of the foot, and is not opposable. It scarcely reaches
the end of the second metatarsal of the second digit, and its functional
importance is minimal. Digits two through five are subequal, although
the third and fourth are a bit longer than the second and fifth, and all
bear well-developed curved claws.

Gregory (1910, p. 211) maintained that in caenolestids:

the pes is entirely eleutherodactylous and shows no trace of the syndactyly so

characteristic of the [Australasian] Diprotodontia.

He further concluded that the pes, as in smaller Australasian
Dasyuridae, is modified for terrestrial and cursorial habits.

Osgood (1921, p. 21) noted that in some specimens of Caenolestes
available to him for study

the third and fourth digits are connected at the base by an integumentary web which

is slightly more extensive than that between the other digits, but this is scarcely to be

regarded as a tendency toward syndactylism.

Lonnberg (1921, p. 77) also noted that in a specimen of Caenolestes
obscurus that he studied, the fourth and fifth digits on the right hind
foot were united along their whole length in a skin sheath. Both exam-
ples are of anomalous individuals, but well illustrate the ease with
which two toes may become united or nearly so.

Little is known of the postcranial anatomy of fossil caenolestids.
Ameghino (1894) described the feet of Santacrucian representatives of
his suborder Paucituberculata as follows:
The four limbs were almost equal in length, but the hind feet were longer than the
fore. They were plantigrade, with five toes on the hind feet and probably also on the
fore feet, with all the toes well developed and without the least trace of syndactyly
(translated from Spanish by Sinclair, 1906, p. 418).

Figures substantiating these observations were not given nor were de-
scriptions of postcranial materials presented. The only described post-

120 FIELDIANA: GEOLOGY

cranial material of fossil Caenolestidae are by Sinclair (1906, p. 423).
These include the distal end of a right scapula, a left humerus, a left
radius, and a left ulna, all attributed to "Garzonia patagonica"
{=Stilotherium dis simile). '

In summary, caenolestids have a didactylous pes and are therefore
plesiomorphic in this feature.

Synopsis of the Characters

The distribution of the characters and their states is summarized in
Table 20. An important feature of this analysis is that the family
Caenolestidae, although clearly a monophyletic group as shown by
features of the dentition (e.g., development of diprotodonty; presence
of a hypocone on M 1 " 3 ; presence of an "intermediate conule" at base of
metacone in M 1,3 ; emphasis of M, in mastication) is largely defined by
retention of characters here considered primitive for the Marsupialia
(e.g., lack of a fasciculus aberrans in forebrain; lack of a pouch; pres-
ence of ossified epipubic bones; diploid chromosome number of 2n =
14; didactylous pes). Some characters distinguish caenolestids from
some or all other marsupial groups, but the polarity is either not surely
known (e.g., sperm morphology) or the polarity of change is not clearly
understood with respect to all other marsupial groups (e.g., presence of
large palatal vacuities; reduction of teat number to 5 or 4). Some
characters establish definite phylogenetic affinity with other marsupial
groups (e.g., sperm pairing in caenolestids and didelphoids shows liv-
ing American marsupials to be a monophyletic group), and some
characters distinguish one caenolestid subfamily from another (e.g.,
presence of an antorbital vacuity in Caenolestinae; number of incisors;
certain structural features of premolars and molars).

Osgood (1921, pp. Ill, 151), based on a detailed study of
Caenolestes, listed several features not discussed above in which it
differs from other living non-caenolestid marsupials. These include: (1)
presence of a large mastoid foramen in adults; (2) a long, narrow
carotid canal between the petrous periotic and basioccipital; (3) floor of
braincase very wide between sphenoidal fissures; (4) mastoid large and
broadly exposed laterally; (5) olfactory fossa relatively large and wide;
(6) very short pubic symphysis; (7) extended articular surface of
trochlea of humerus; (8) sesamoid in tendon of m. extensor cruris
[among marsupials a patella is reported elsewhere only in perameloids
(Winge, 1923) and borhyaenoids (Sinclair, 1906)]; and (9) stomach with
three marked divisions (the cardiac gland of the stomach has a coun-
terpart only in Phascolarctos and Vombatus).

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126 FIELDIANA: GEOLOGY

The polarity of each of these characters needs to be firmly
established, although they appear to be potentially useful in
phylogenetic studies. If nothing else, they reaffirm the uniqueness of
caenolestids compared with other marsupial groups. I list these here
for the sake of completness, but do not attempt a cladistic analysis of
them at this time.

Phylogenetic Relationships of Caenolestid Subfamilies

Three major monophyletic lineages occur among known fossil and
living Caenolestidae. These are regarded as warranting subfamilial rec-
ognition and include the Caenolestinae, Palaeothentinae, and Ab-
deritinae. These subfamilies share a number of apomorphies that dis-
tinguish them from some or from all other marsupial groups, and the
joint possession of these apomorphies establish the monophyletic ori-
gin of the family Caenolestidae. These apomorphies include: reduction
in incisor number to at most I; palatal vacuities present; diprotodonty;
most antemolar teeth greatly reduced in size; hypocone present on
M 13 ; loss of stylar shelf; sharp size decrease of molars from Ml to M4;
"intermediate conule" present at inner base of metacone in unworn
M 13 ; M 1 quadritubercular; talonids of M 2 . 3 much larger in occlusal view
than trigonids; teats five or four in number; sperm paired; and sperm
rectilinear, with notch on one side from which mid-piece arises. The
unique position of caenolestids among the Marsupialia is further
established by studies of serum proteins (Kirsch, 1977a).

The one uniquely derived character of great importance in
phylogenetic inference is the occurrence of sperm "pairing" in
caenolestids and didelphoids. This feature clearly shows the American
marsupials to be a monophyletic group relative to those in Australasia,
and it further clarifies the major trichotomy in marsupial phylogeny
implied by the serological studies of Kirsch (1977a, fig. 23).

Two tribes of Caenolestinae, the Caenolestini and Pichipilini, are
recognized. Members of the Caenolestini are the most generalized of
caenolestids, and they retain the larger number of states regarded as
plesiomorphic for the Marsupialia. This tribe has the longest geological
range of any caenolestid group (Casamayoran to Recent), and it repre-
sents the basal stock from which may be derived the Pichipilini and the
subfamilies Palaeothentinae and Abderitinae. The plesiomorphic states
possessed by Caenolestini include: P 2 with two roots; P 3 large, two
rooted, and of equal or greater height than M,; trigonid and talonid
regions of M, distinct and unmodified; the paraconid on M 2 _ ;{ large and
distinct. Members of the Caenolestini possess no apomorphous states

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 127

not shared with Pichipilini; they are distinguished from Pichipilini by
possession of plesiomorphic states of the subfamily.

Apomorphous states possessed by Pichipilini, which separate them
from Caenolestini, include: P : , of equal or less height than M,;
paraconid very reduced on M 2 .. { ; trigonids narrower than talonids;
trigonid cusps equal to or only slightly higher than talonid cusps;
talonid basin broad and relatively shallow; and cuspule present pos-
terior to lingual trigonid cusp on M,_ 3 .

The common possession of an antorbital vacuity between the nasal,
frontal, and maxillary in both Caenolestini and Pichipilini is a unique
apomorphy that establishes the Caenolestinae as a monophyletic
group.

The subfamilies Palaeothentinae and Abderitinae are monophyletic
and shared a common ancestor that possessed the following apomor-
phies: incisor number reduced to £, mandibular ramus relatively shorter
and deeper than in Caenolestini; molars brachyodont; protoconid-
paraconid crest on M, trigonid becomes elongated but not blade-like;
sectorial occlusion developed between posterolingual edge of enlarged
P and protoconid-paraconid crest of M, trigonid; paraconid is reduced
in size and is virtually lost on M 2 . ;{ ; trigonid and talonid regions of M 2 _ ; ,
subequal in size in occlusal view and in height in lateral view; and
talonid basin shallow.

The Palaeothentinae retained most of these features without change,
but are further distinguished from Abderitinae in hypertrophy of the P 3 .
Some Palaeothentinae (i.e., species of Acdestis) have the additional
apomorphies of a single-rooted P 2 , and the P 3 is small, sometimes single
rooted, and less than V2 the height of M,.

Some Palaeothentinae retain features shared with Caenolestini, but
which are lost in other Palaeothentinae and in all Abderitinae. In
Palaeothentes minutus these include: presence of an "intermediate
conule" in unworn M ,:J ; P 2 double rooted in some specimens; P :{ equal
to or greater in height than M,; and retention of the "stamp" of a
tuberculo-sectorial dentition. Palaeothentes minutus thus forms a link
between the subfamilies Caenolestinae and Palaeothentinae.

Two tribes of Abderitinae, the Parabderitini and Abderitini, are rec-
ognized. The Abderitinae are a monophyletic group as indicated by the
common possession of the following apomorphies: P 2 single rooted;
molars bunolophodont; "intermediate conule" completely lost;
trigonid of M, large, blade-like with serrated edge, and greatly elevated
above rest of tooth row; and metaconid lost from M,.

128 FIELDIANA: GEOLOGY

The Parabderitini retained the large P :! as occurs in most Palaeothen-
tinae and Caenolestini and incorporated it as a sectorial. The sectorials
in Parabderitini include P :{ (?) above and the P ;j and trigonid of M,
below. The P 2 is separated from the P :! by a distinct diastema in Parab-
deritini, but not in Abderitini or in Palaeothentinae or Caenolestinae.
Thus, the dental specializations seen in Parabderites simply represent
further development of those occurring in the genus Palaeothentes
among the Palaeothentinae.

The Abderitini represent the most specialized of known caenolestids
and are distinguished by possession of the following apomorphies: P. {
very small, single rooted, styliform, and set in notch in anterobasal
edge of M,; distinct accessory cuspule present anterior to paracone on
M 2 ~ :! ; M 1 blade-like and with a serrated edge and talonid very reduced;
sectorials are M 1 above and trigonid of M, below; and trigonid and
talonid regions of M 2 . ;i are typically difficult to differentiate.

Sinclair (1906, pp. 417-418) adduced evidence to show that the
plagiaulacoid M, in Abderites was derived from a tuberculo-sectorial
M, as occurs in such caenolestines as Caenolestes. he further
suggested that the structural change passed through an intermediate
stage as seen in some Palaeothentinae. These views are ratified by the
present study. The tribes and subfamilies of Caenolestidae form a
structural series, and one group is readily derivable from another. It is
thus possible to construct an evolutionary series based on known mor-
phologic types. In the following diagram, change occurs from left to
right along the horizontal axis, and dorsodextrally along the vertical
axis:

Pichipilini (Acdestis) Abderitini

Caenolestini -* Palaeothentinae (Palaeothentes) — » Parabderitini

One implication of the foregoing analysis is that size reduction of the
P ;i occurred independently in all three subfamilies. In the Caenolestinae
it occurred in the Pichipilini (Pliolestes), in the Palaeothentinae it oc-
curred in Acdestis, and in the Abderitinae it occurred in the Abderitini.
This size reduction is regarded as a convergent feature in which the
ancestral form had, in all cases, a large two-rooted P :! . Thus, Abderites
did not evolve from an ancestral palaeothentine such as Acdestis, but
from a form with a large, two-rooted P :! like Palaeothentes.

The time of the didelphoid-caenolestoid dichotomy is not certain and
is open to broad speculation. Based on present knowledge, two points
appear certain; one that the split occurred in South America, and two
that the Caenolestidae are, in the strictest sense, monophyletic.

MARSHALL: SYSTEM ATICS OF CAENOLESTIDAE 129

The earliest record of fossil marsupials in South America comes from
the Laguna Umayo local fauna in Peru, considered to be of Late Cre-
taceous age (fide Sige, 1972). The marsupial fauna includes two species
of didelphoids (Sige, 1972; Crochet, 1979). These animals are known
exclusively from a few isolated or broken tooth fragments. The di-
versity of this fauna has yet to be determined, and absence of forms
known from later faunas carries little significance at this time. Absence
of caenolestids does not necessarily indicate that they were not present
at this locality or that they did not exist elsewhere.

Caenolestids are also unknown in the rich Riochican fauna of
Itaboraf, Brazil, in which many small marsupials are found. However,
one Riochican species, Derorhynchus singularis Paula Couto (1952a, p.
15) displays a number of features that are reminiscent of living
caenolestids. These include: a slender elongated mandibular ramus; a
long symphysis; a well-developed, procumbent, laterally compressed,
and probably very elongate I,; and in general reduction in size of an-
temolar teeth on the symphysis. Paula Couto (1952a, p. 15) concluded
that this species was convergent with caenolestids, and he accordingly
classified it in the family Didelphidae, subfamly Didelphinae.

It must be stressed that of the 13 genera and 14 species of marsupials
referred by Paula Couto (1952a, 1961, 1962, 1970) to the Didelphidae,
all are based on preliminary original descriptions. He neither attempted
to evaluate the relationships of these forms among each other, nor to
compare them with possible ancestral forms from the Late Cretaceous
of North America or with contemporaneous or later taxa elsewhere. As
a result, the taxonomic diversity of these forms has not yet been fully
realized. Simpson (1971, p. 112) has noted, and I agree, that at least
subfamilial division is warranted, but these divisions have not yet been
established. These didelphoids seem to be as varied as the didelphoids
from the Lance Formation of North America that Clemens (1966) puts
in three families, one with two subfamilies.

It is now generally agreed that all Cenozoic marsupial groups
evolved from didelphoids or didelphoid-like ancestors. It is thus im-
portant to understand the phylogenetic relationships of these Riochican
forms with each other and with other groups. These Riochican di-
delphoids represent the earliest documented radiation of marsupials in
South America, and they provide a "key" to understanding the
phylogenetic relationships of all other South American marsupial
groups.

The critical point with regard to this study is that ancestral forms for
the family Caenolestidae may exist among known Riochican di-
delphoids, but if so they have not been recognized as such. This will

130

FIELDIANA: GEOLOGY

only be possible pending a detailed phylogenetic study of these Riochi-
can taxa. All that can be said for now is that caenolestids are not known
or are not recognized in beds of pre-Casamayoran age.

Caenolestids are first known from a single isolated partial lower
molar from beds of Casamayoran age in Patagonia. Little can be said
about the affinities of this tooth with other caenolestids or with other
marsupial groups. This tooth is however the oldest specimen of the
family Caenolestidae yet known, and it records a minimal age for the
appearance of this family.

The fossil record of caenolestids begins, for all practical purposes, in
the Deseadan. Relatively complete representatives of each of the three
subfamilies have been found in beds of this age in Argentina. Further, a
member of the Palaeothentinae is known from the Deseadan of Bolivia.
The three subfamilies are clearly distinguishable at this time, indicating
an earlier radiation for the family.

The above data indicate that a member of the generalized caenolestid
subfamily Caenolestinae was present by Casamayoran time and that
the more specialized subfamilies Palaeothentinae and Abderitinae
(which are derivatives of the Caenolestinae) are present in the De-
seadan. The didelphoid-caenolestoid dichotomy clearly occurred be-
fore the Casamayoran, whereas subfamily differentiation within the
Caenolestidae was a pre-Deseadan event.

The cladogram in Figure 36 is a graphic summary of the above re-
lationships, based upon an analysis of shared-derived character states.

Caenolestinae Palaeothentinae Abderitinae

ienolestini Pichipilini Parabderitini Abderitini

10

Fig. 36. Cladogram showing probable relationships of suprageneric groupings of
Caenolestidae. Diagram shows only relative position of common ancestor. Numbers
indicate character state distribution.

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 131

Key to Figure 36:

1, Plesiomorphic character states for Marsupialia — these are listed in Table 20, column
1.

2, Apomorphies for Caenolestidae: I}, C|, Pj, M}; palatal vacuities present; di-
protodonty; most antemolar teeth greatly reduced in size; hypocone present on M 1 "' 1 ;
no stylar shelf; sharp size decrease of molars from Ml to M4; "intermediate conule"
present at inner base of metacone in unworn M 11 ; M 1 quadritubercular; talonids of
M 2 . :I much larger in occlusal view than trigonids; teats 5 in number; sperm paired;
sperm rectilinear with notch on one side from which mid-piece arises.

3, Apomorphies for Caenolestinae: I s i|, CJ, Pjj, M]: antorbital vacuity present between
nasal, frontal, and maxillary.

4, Apomorphies for Caenolestini: None known — tribe retains only plesiomorphic states
for subfamily.

5, Apomorphies for Pichipilini: paraconid very reduced on M 2 . :! ; trigonid cusps of M 2 . ;1
equal to or only slightly higher than talonid cusps; talonid basin broad and relatively
shallow; cuspule present posterior to lingual trigonid cusp on M,. :t .

6, Apomorphies for immediate common ancestor of Palaeothentinae and Abderitinae:
I:], C|, P{, Mj; mandibular ramus relatively shorter and deeper; molars brachyodont;
protoconid-paraconid crest of M, trigonid elongated but not blade-like; sectorials
PVM, triuoni,!; paraconid virtually lost on M M ; trigonid and talonid regions of M 2 . :t
subequal in size in occlusal view and in height in lateral view; and talonid basin
shallow.

7, Apomorphies for Palaeothentinae: P 2 single rooted in some forms; P., in some forms
small, single rooted, and less than Vi the height of M,; "'intermediate conule" lost in
some forms; P' large with posterolingual shear surface.

8, Apomorphies for Abderitinae: P 2 single rooted; molars bunolophodont; "inter-
mediate conule" lost; trigonid of M, large, blade-like, and greatly elevated above
rest of tooth row; loss of M, metaconid.

9, Apomorphies for Parabderitini: P :1 large, two rooted, and blade-like: sectorials
PV.'VPi-M, trte>iiid< F2 separated from P, by distinct diastema.

10, Apomorphies for Abderitini: mandibular ramus relatively shorter and deeper; P.,
very small, single rooted, styliform, and set in notch in anterobasal edge of M,
distinct accessory cuspule present anterior to paracone on M 2:! : M 1 blade-like
trigonid of M, very large, blade-like with serrated edge, and talonid very reduced
sectorials M'/M, lr j», n ict; trigonid and talonid regions on M 2 . : , typically difficult to
differentiate.

DISCUSSION AND CONCLUSIONS

During the Cenozoic in South America, the ecological roles of small
mammal niches were filled in part by members of the family Caenoles-
tidae. Caenolestids reached their known evolutionary climax in the
mid-Tertiary (i.e., Santacrucian-Early Miocene time) when they were
represented by three known subfamilies, seven genera, and 1 1 species.
In beds of this age, caenolestids are the most abundant and the most
taxonomically diverse of the small Marsupialia.

Factors influencing the times of origin, adaptive radiation, decline in
diversity, and/or extinction of the various caenolestid groups are com-
plex, but most of these events are correlated with the appearance
and/or diversification of other mammalian groups. Thus, there oc-
curred in South America successive replacement through time of (and
by) different groups of animals stemming from different lineages but
occupying the same adaptive zone. These "ecological replacements"
or " 'evolutionary relays"' may have resulted from active competition
between the successive groups filling these roles or from passive re-
placement resulting from the disappearance of one group due to chance
processes or as a result of concurrent environmental changes.
Alternatively, such faunal changes were the result of a combination of
these or of other possibilities.

The polydolopoids, a marsupial group with plagiaulacoid dental spe-
cializations, were taxonomically diverse in beds of early Tertiary age in
South America. They declined in diversity after Casamay oran time and
make their last appearance in the Deseadan of Bolivia (Patterson &
Marshall, 1978, p. 95). It is either coincidental or significant that this
group's last appearance coincides with the first documented appear-
ance of caviomorph rodents in South America. It is generally agreed
that polydolopoids were somewhat rodent-like in structure and ecology
and may thus have been replaced by these rodents in the Early
Oligocene.

Abderitines also make their first appearance in the Deseadan of
Patagonia. They thus occur contemporaneously with polydolopoids.

132

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 133

but the two groups were allopatric in their geographic distribution;
Deseadan abderitines are known only from Patagonia, southern
Argentina, whereas Deseadan polydolopoids are known only from
Bolivia. Abderitines and polydolopoids were very similar in dental
morphology and presumably in ecology as well. It is tempting to
speculate that abderitines rather than the caviomorph rodents were, at
least in part, the ecological replacements of polydolopoids. The sub-
family Palaeothentinae also appears in the Deseadan and may likewise
have evolved to help fill part of the adaptive zone in the mid-Tertiary
that was occupied by polydolopoids in the early Tertiary. Evolution of
the Abderitinae and Palaeothentinae may thus have been triggered by
the vacated or opening adaptive zone for small terrestrial omnivores-
herbivores and may have been linked with the decline to extinction of
the marsupial superfamily Polydolopoidea.

The appearance of caviomorph rodents in the Early Oligocene may
or may not have been an influence on the decline to extinction of the
polydolopoids. The appearance of these rodents certainly did not ap-
pear to hinder the evolutionary potential of abderitines and
palaeothentines. Caviomorph rodents and these groups of caenolestids
appear at the same time in the fossil record of South America and
underwent successful concurrent and apparently sympatric adaptive
radiations.

There is some suggestion that the abderitines and palaeothentines
were at least in part competitively exclusive. The ratio of species of
Abdertinae to Palaeothentinae in the Deseadan of Patagonia is 1:3, in
the Colhuehuapian it is 4:1, and in the Santacrucian it is 2:5. Thus, in
Patagonian faunas of a given Age one subfamily is dominant in species
diversity over the other. These differences may be the result of some
form of competitive interaction between members of these groups, or,
alternatively, may simply be attributed to an artifact of sampling.

Causes of the post-Santacrucian decline to extinction of the Abder-
itinae and Palaeothentinae are obscure, but appear to be linked with
major climatic and concomitant ecological changes. During the late
Miocene and Pliocene, the Argentine sedimentation center shifted from
Patagonia to the pampas and northwestern regions. The sediments
changed from predominantly pyroclastic (i.e., tuffs and bentonitic
clays) that characterize pre-Chasicoan units, to predominantly clastic
{i.e., silts, sands, and clays) that predominate post-Friasian units of the
pampean region. This change of sediment type coincided with a post-
Friasian phase of Andean orogeny that was to result in elevation of the
Andean Cordillera. A major period of orogenic activity occurred be-

134 FIELDIANA: GEOLOGY

tween 4.5 and 2.5 mybp and resulted in an increase in elevation of 2,000
to 4,000 meters. Elevation of the Andean Cordillera acted as a barrier
to moisture-laden Pacific winds. The southern South American habitat
changed from primarily savanna-woodland (which predominated dur-
ing the early to middle Tertiary-Eocene through Miocene) to drier
forests and pampas, ranging from forests in the northern parts of the
continent to grasslands in the south. There was initiated the de-
sertification of Patagonia, caused by the rain shadow effect of the
newly elevated Andes. Pampas environments, predecessors of those
prevailing today, probably came into prominence at this time. Many
subtropical savanna- woodland forms retreated northward, and new
opportunities arose for those mammals able to adapt to a plains envi-
ronment (Marshall et al., In press and references therein). Those
groups that neither moved nor adapted became extinct. Such was the
apparent fate of the Abderitinae and Palaeothentinae.

One caenolestid group, the Pichipilini, did however adapt to these
new conditions. A specimen of Pliolestes sp. is known from beds of
Chasicoan age, and several specimens of P. tripotamicus are known
from faunas of Montehermosan age from localities in the southwestern
corner of Buenos Aires Province, Argentina. Pascual & Herrera (1973)
have suggested that extinction of these marsupials may have been
caused by competitive interaction with cricetine rodents that first ap-
pear in the South American fossil record in beds of Montehermosan
age in the Province of Buenos Aires (Marshall, 1979a and references
therein).

The only living caenolestids are members of the tribe Caenolestini.
These are the most generalized of all known Caenolestidae, and they
are carnivorous-insectivorous in their feeding habits. They are shrew-
like in morphology and ecology and occur throughout the west coast of
South America, from the Andes of Colombia and Venezuela in the
north to southern Chile in the south. Caenolestini have apparently filled
their present roles since the early Tertiary and have not been seriously
challenged for them by invading ecologically similar groups during any
time in their evolutionary history.

Their position may now be threatened. Members of the placental
family Soricidae have recently invaded the northwestern corner of
South America (Hershkovitz, 1972). They came from North America
across the Panamanian Land Bridge that became established about 3
my ago (see Marshall, 1979a, and references therein). The family is
represented by one genus, Cryptotis, which occurs sympatrically with
species of Caenolestes over parts of its range. Cryptotis is significantly

MARSHALL: SYSTEMATICS OF CAENOLESTIDAE 135

smaller in size than Caenolestes, and this difference may explain or
permit their sympatry. However, the biological consequences of po-
tential competition between these groups is not yet fully understood or
evident, but both are similar in structure and presumably in ecology as
well. Thus, there may be an active "evolutionary relay" in progress,
and the caenolestines may be in jeopardy. If so, the Caenolestini may
well join the ranks as a fossil group along with their more specialized
bygone relatives.

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