Late Cretaceous mammals (Marsupialia) from Bolivia

LATE CRETACEOUS MAMMALS (MARSUPIALIA) FROM BOLIVIA

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LARRY G. M A R S H A L L *, CHRISTIAN D E MUIZON ** & BERNARD SIGI~ ***

ABSTRACT RI~SUMt~

A second Late Cretaceous (Maestrichtian Age) mammal fauna for South America was recovered from the E1 Molino Formation in southcentral Boli- via. Three species are referred to the marsupial superfamily Didelphoidea. The most abundant species has marked bunodont dental specializations which are convergent with some early placental Condylarthra ; it is named and is tentatively placed in the didelphid subfamily Caroloameghiniinae.

La deuxi~me faune ~t mammif6res du Cr6tac6 sup6- rieur (Maestrichtien) d'Am6rique du Sud a 6t6 d6cou- verte dans la Formation E1 Molino au Centre-Sud de la Bolivie. Trois esp~ces sont r6f6r6es /t la super- famille marsupiale des Didelphoidea. L'esp~ce la plus commune pr6sente une sp6cialisation dentaire buno- donte, convergente avec celle de quelques placentaires condylarthres anciens ; elle est nomm6e et plac6e en premiere analyse dans la sous-famille des didelphid6s Caroloameghiniinae.

KEY-WORDS : BUNODONT MARSUPIALS, CAROLOAMEGHINIINAE, LATE CRETACEOUS, SOUTH AMERICA.

MOTS-CLI~S : MARSUPIAUX BUNODONTES, CAROLOAMEGHINIINAE, CRI~TACI~ SUPI~RIEUR, AM1~RIQUE DU SUD.

We describe and name the most complete fossil mammal yet known for the Late Cretaceous (Maes- trichtian) of South America. Two other mammals are described but not named. These fossils were collected from 125 meters above the base of the E1 Molino For- mation at Tiupampa, 6 km southeast of the pueblo Vila Vila and about 95 km southeast of Cochabamba, southcentral Bolivia (1).

Previous to our discovery the only Late Cretaceous mammals known for South America were from the Laguna Umayo local fauna of the Vilquechico For- mation near Lake Titicaca, Peru. Three species of mammals are known only from tooth fragments. Perutherium altiplanense was originally questionably referred to the placental order Condylarthra (2) and

later (3) formally placed in the condylarth family Periptychidae, subfamily Perutheriinae. A second species, Alphadon austrinum, was placed in the marsupial family Didelphidae (4), and the species austri- hum was later assigned to the genus Peradectes (5). A third species possibly represents a member of the marsupial family Pediomyidae (4, 6), a group common in North American Late Cretaceous deposits (7). Addi- tional tooth fragments of more questionable identity are also known (6).

In South America marsupial and placental mammals are first abundantly known from rocks of Rio- chican Age in Argentina and Brazil (8). Riochican was conventionally regarded as Late Paleocene (8, 9), but recent geochronological studies of rocks and faunas

* Department of Geosciences, University of Arizona, Tucson, Arizona 85721, U.S.A. ** Institut de Pal6ontologie (LA 12, CNRS), 8 rue de Buffon, 75005 Paris, France. *** Laboratoire de Pal6ontologie (LA 327, CNRS), U.S.T.L., Place Eugene Bataillon, 34060 Montpellier Cedex, France.

Geobios, n ° 16, fasc. 6 p. 739-745, 2 fig., 1 tabl. Lyon, d6cembre 1983

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of this age in Patagonia, southern Argentina, show that Riochican there encompasses Middle and Late Paleocene (10), while the Riochican fissure fillings at Itaborai, Brazil, may be Early Paleocene (11).

The specimens described below are catalogued in the collection of the Institut de Pal6ontologie, Mus6um national d'Histoire naturelle (MNHN), Paris, France. Terminology for cheek tooth morpho- logy follows (12), and the serial designation for cheek tooth number follows the conventional dental formula for marsupials of three premolars and four molars. The following abbreviations are u s e d : L , length ; M, molar ; P, premolar ; W, width.

Superfamily DIDELPHOIDEA

Family Didelphidae Subfamily ? Caroloameghiniinae

Genus Roberthoffstetteria new genus

ETYMOLOGY. Roberthoffstetteria, in honor of Pro- fessor Robert Hoffstetter (MNHN) in recognition of this contributions to knowledge of mammalian evolution in South America in general and in Bolivia in particular (13) (note infra. 1).

(note infra. 1) - The coining of scientific generic names by uniting given and family names was done by the Argentine paleontologist Florentino Ameghino at the turn of the last century. A list of these names is given by G.G. Simpson.

TYPE. Roberthoffstetteria nationalgeographica new species (see below).

DISTRIBUTION AND DIAGNOSIS. As for type and only known species.

Roberthoffstetteria nationalgeographica new species

(fig. I a-f)

ETYMOLOGY. nationalgeographica, for the National Geographic Society which sponsored the field work and made the discovery of this animal possible.

HOLOTYPE. MNHN Vil. 99, a right maxilla with p1 and p2 complete, base of p3 and M 1 to M 4 complete.

HYPODIGM. Type and MNHN Vii 100, a partial left mandible with M1 to M4 complete ; MNHN Vii 101, a par t ia l left mand ib le with M1 to M 3 complete ; MNHN Vii 102, a partial left mandible with roots of M 3 and M4 complete ; MNHN Vii 117, an isolated left M1 ; and probably MNHN Vii 109, a partial right mandible with anterior root and hypoconid of M4 preserved.

M1 M2 M3 M4

specimen L W L W L W L W

upper cheek teeth

MNHN Vii 99* 2.57 3.10 2.88 3.84 2.93 4.05 2.49 3.30

lower cheek teeth

MNHN Vil I00 2.56 1.96 2.77 2 35 3.07 2.37 3.29 2.52

MNI4N Vil i01 2.37 1.71 2.80 2.11 3.21 2.47 ........

MNHN Vii 102 . . . . . . . . . . . . . . . . . . . . . . . . 3.32 2.52

MNHN Vii 117 2.59 1.97 . . . . . . . . . . . . . . . . . . . . . . . .

* pl L = 1.04, W = 0.84; p2 L = 2.05, W = 1.31; p3 L = 2.64, W = 1.68

Tabl. 1 - - Measurements (in mm) of cheek teeth of Roberthoffstetteria nationalgeographica new genus and new species (for abbreviations see text.).

Dimensions (en ram) des dents jugales de Roberthoffstetteria nationalgeographiea nov, geu. et nov. sp. (pour les abbrgviations, voir le texte).

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DIAGNOSIS. Medium size didelphoid (note infra. 2) ; known cheek tooth formula p3 M~-; premolars trenchant and unspecialized ; molars markedly bunodont, cusps bulbous ; M 1 to M 3 with large stylar shelf and five distinct stylar cusps (cusp B prominent) ; para- and metaconules well developed and in extreme lingual position next to protocone, the three together form a ridge with axis parallel to that of tooth row ; trigonid only slightly higher than talonid ; entoconid and hypoconulid separate and not distinctly ~ twinned ~ as is typical in other didelphoids (7).

DESCRIPTION. Infraorbital foramen large, located dorsal to P3 ; premolars trenchant, unspecialized, increasing in size from p1 to p3 ; p1 has small posterobasal cuspule; P2 has large posterobasal cusp, large basalcingulum posterolingually, and weak basalcingulum anterolingually ; p3 apparently structurally similar to p2 as inferred from preserved basal portion of tooth (fig. 1 a-c, table 1).

On uppers molars trigon and primary stylar cusps subequal to height and on same occlusal level ; M1 to M4 have well developed para- and metacingula (latter absent on M 4) ; proto-, para-, and metacones large, rounded;pro to- and paracone subequal in size, metacone slightly larger on M1 to M3 ; M 4 proto-and paracone large, subequal in size, metacone very reduced and possibly fused with stylar cusp E ; para-and metaconule well developed on M1 to M4, metaconule slightly larger and more distinct than paraconule ; meta- and paraconule situated in extreme lingual position, paraconule set at anterolabial corner of protocone, metaconule set immediately posterior to protocone ; a small accessory cuspule occurs on rnetacingu- lum just posterior to metaconule (best seen on M1 and M3) ; no trace of centrocrista and only hint of paracrista ; stylar shelf with five distinct cusps on M1 to M3 ; stylar cusp A small on M1 to M4 ; stylar cusp B most prominent of stylar cusps : on M1 subequal in size to stylar cusp D, on M2 and M3 enormous and subequal in size to paracone, on M4 small ; stylar cusp C large on M1 to M3, set lingual of stylar cusps B and D, and almost centrally situated between stylar cusps B and D, and para- and metacone ; stylar cusp D very large and subequal in size to stylar cusp B on M1, only slightly smaller than stylar cusp B on M2,

(note infra. 2) - Of the three size groupings of living and Neoceno- zoic didelphoids recognized by (12) (small, medium, large), Rober- thoffstetteria falls in the medium group.

small on M3 and M4 ; stylar cusp E very small on M 1 to M3, absent on M 4 ; ectoflex distinct on M1 to M3 and accentuated by bulbous labial swelling of inflated stylar cusps B and D ; ectoflex small but distinct on M 4 ; on MI to M3 transverse row of cusps formed by stylar cusp B-paracone-protocone, and a second row formed parallel to first by stylar cusp D-metacone- metaconule (fig. 1 a-c, tabl. 1).

Mandibular ramus has angular process inflected medially ; mandibular foramen located below middle of M 1 ; o n lower molars anterobasal cingulum weakly developed ; a small cingulum extends ven- trally from labial side of hypoconulid to basolabial edge of hypoconid on M 3 ; trigonid slightly higher than talonid in labial view, subequal in size in occlusal view ; M1 trigonid slightly narrower than talonid, trigonid and talonid subequal in breadth on M2 and M3, trigonid broader than talonid on M4 ; hypoflexid deep on M1 to M4 ; entoflexid weakly developed on M1 and M2, absent on M3 and M4 ; proto- and metaconid well developed, subequal in size and height on M1 to M4 ; protoconid becomes absolutely larger from M1 to M4, being principal cusp on M4 ; paraconid notably smaller and lower than protoconid and metaconid on M1, relatively larger on M2, subequal in height to protoconid and metaconid on M 3 and M4 ; a weak paracristid extends down anteromedial side of protoconid connecting to anterobasal part of paraconid ; a weak crista obliqua connects anterior edge of hypocone with posterolingual edge of protoconid ; entocristid weakly developed on M1 to M3, better developed on M4 ; hypoconid slightly larger than entoconid on M 1 to M4 ; hypoconulid distinct on M 1 to M4, and although closer to entoconid than to hypoconid, it is situated almost medially at posterior end of talonid basin (fig. 1 d-f, table I).

COMMENTS. The upper and lower dentitions were not found in association. But they are from the same level, the size and structure of the molars are comple- mentary, and we confidently refer them to the same species. The marsupial affinities are established by the joint occurrence of four permanent molars, a stylar shelf with five stylar cusps on M1 to M3 of which stylar cusp B and D are large and prominent, and a medially inflected angular process on the mandible (14).

Of known didelphoid marsupials Roberthoffstette- ria is most similar in size and gross structure of the

l a

l b

l c

\

l d

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l e

I f

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bunodont molars to Procaroloameghinkt (Didelphi- dae, Caroloameghiniinae) from fissure fillings of Rio- chican age at Itaborai, Brazil (15). Procaroloameghi- nia is known only by a mandible with P1 to M4. These taxa differ in Roberthoffstetteria having a relatively and absolutely larger M4, distinct entoconid and hypoconulid, more bulbous cusps, a narrower talonid with a relatively larger hypoconid and a weaker crista obliqua, a more weakly developed anterobasal cingu- lure, a relatively and absolutely larger protoconid, and smaller para- and metaconids which are approxi- mated and enclose the prefossid. Roberthoffstetteria is thus more specialized in these features relative to a hypothetical dedelphoid ancestor (12) than is Proca- roloameghinia. Consequently, Roberthoffstetteria cannot represent a structural ancestor of Procaroloa- meghinia but the two may have shared a common ancestor which had some tendency toward bunodonty. Structurally, this hypothetical ancestor would have been more like Procaroloameghinia than like Roberthoffstetteria which represents the more specialized of the two lineages. In view of this we tentatively place Roberthoffstetteria in the didelphid subfamily Caroloameghiniinae.

Roberthoffstetteria also shares bunodonty with the North American Late Cretaceous didelphid Glasbius (Glasbiinae) (7), hut little else. The differences are great and the noteworthy ones include Roberthoffs- tetteria having a predominant stylar cusp B on M2 and M3 (in Glasbius stylar cusp D is predominant) ; para- and metaconules are in extreme lingual position next to protocone ; trigon is more reduced (shallo- wer) ; para- and metacone are smaller relative to protocone and stylar cusps B and D ; M4 is much larger and is subequal in size to M3 (in Glasbius M 4 is reduced) ; labial cingulum is very reduced (in Glasbius it is enormous and extends along entire labiobasal surface of M1 to M4) ; hypoconulid is distinct (absent or ves- tigial in Glasbius) ; and trigonid is more reduced and talonid is narrower relative to it than occurs in Glas- bius.

Perutherium from the Late Cretaceous of Peru is also bunodont, and a possible affinity with the marsupial subfamily Caroloameghiniinae has been sugges- ted for it (16). Indeed, in having a postmetastylid Perutherium resembles the Early Eocene didelphid Caroloameghinia (Caroloameghiniinae) (15) and some Early Tertiary Polydolopidae (17); further similarity is expressed in reduction of the trigonid. Yet, a distinct postmetastylid also occurs in Early Ter- tiary notoungulates (18) and further common structu- res include possession of a premetastylid and preme- tacristid (features unlike those seen in marsupials), and an anterolingual basalcingulum. These and other (3) features favor placental rather than marsupial affinity. Furthermore, Sig6 (6) refers a fragment of an upper molar to Perutherium and its possession of what he interprets as a possible hypocone is further evidence favoring placental affinity. Thus, apart from general bunodonty, Perutherium shows no special affinity to Roberthoffstetteria.

Nevertheless, some features of Roberthoffstetteria are convergent with some Early Tertiary Condy- larthra (e.g. bunodonty, relative importance of protoconid, multiple cusps lingually on upper molars (3, 18, 19). These condylarth-like specializations of Roberthoffstetteria are of particular interest since placentals resembling condylarths are unknown in the fauna at Tiupampa. It appears likely that Rober- thoffstetteria was filling a role in this area of South America that small condylarths (e.g. Protungulatum) were filling in North America.

Family i n d e t e r m i n a t e

I n d e t e r m i n a t e s p e c i e s A

(fig. 2)

A second species of marsupial is represented by a partial upper right M 4 (MNHN Vii 103) with

Fig. 1 --

Fig. 2 --

1 2 a-f, Roberthoffstetteria nationalgeographica new genus and new species, a-c, MNHN Vil 99 (TYPE) a right maxilla with P and P complete, base of p3, and M 1 to M4~complete. d-f, MNHN Vil 100, a partial left mandible with M 1 to M 4 complete, a & f : labial, b & d : occlusal, c & e : lingual views. Scale : 1 turn. a-f, Roberthoffstetteria nationaigeographica nov. gen., nov. sp., a-c, (TYPE), maxillaire dr. avec p1, p2, base de p3, M1.M 4. d_f, fragment mandibulaire avec M1-M 4. a & f : vues labiales, b & d : occlusales, c & e : linguales, l~chelle : 1 mm.

Marsupial, Family indeterminate, Indeterminate species A. MNHN Vii 103, partial right M 4, occlusal view. Scale : I ram. Marsupial, Famille ind~termin~e, Esp~ce ind~termin~e A., fragment de M 4 dr., vue occlusale.

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paracone, most of metacone, and greater part of stylar shelf. The tooth is large by didelphoid standards (12) and is comparable in size (labial width --- 4.40 ram) and general structure to that of living species of Didelphis. It has a large paracone which is higher and about twice the size of the metacone ; a well developed paracingulum ; a large paracrista (slightly convex anteriorly) ; the area of the stylar shelf labial to the metacone is convex lingually with a slight crest possibly representing a remnant of stylar cusps ; and a narrow trigon basin bordered by small para- and metaconules (fig. 2).

Indeterminate species B

A third species of marsupial is represented by a partial edentulous left mandible (MNHN Vil 108) preser- ving three complete and two partial alveoli, possibly representing those for P3, M1, and anterior root of M2. A small foramen is located below what we believe to be the posterior alveolus of P3. By didelphoid standards (12) this specimen is small, and is comparable in size to Derorhynchus singularis from Itaborai, Brazil (20). The three complete alveoli measure 3.33 mm in length.

CONCLUSIONS

Three taxa, represented by eight specimens of jaws and teeth (note infra. 3), from the Late Cretaceous (Maestrichtian) E1 Molino Formation at Tiupampa, Bolivia are conservatively referred to the marsupial superfamily Didelphoidea. By didelphoid standards (12) these taxa are of small, medium, and large size. The most completely known and abundant species is Roberthoffstetteria nationalgeographica which is convergent with Late Cretaceous and Early Tertiary Condylarthra of North America. The known diversity

(note infra. 3) - Postcranial bones of mammals, all believed to be marsupial, were also recovered by surface collecting. These include a calcaneum (MNHN Vii 104), a partial associated skeleton with calcaneum and phalanges (MNHN Vil 105), the distal end of a femur (MNHN Vil 106), and the distal end of a humerus (MNHN Vil 107). Matrix from the fossil mammal level is presently being washed and sorted for recovery of additional skeletal and dental elements.

of marsupials in the Late Cretaceous local faunas of Tiupampa, Bolivia and Laguna Umayo, Peru (6) and the documented diversity of marsupials in the Riochi- can fauna of Itaborai, Brazil (with at least 16 genera representing three superfamilies : 21), demonstrate an early and broad radiation for this group in South America. This established diversity requires a greater antiquity for marsupials in South America before their first known in the Late Cretaceous. Of the many models proposed for the origin and early biogeogra- phic history of marsupials (22) we interpret these facts as favoring the following model which we also pre- fer : Marsupials originated either on the continent of South America or on a southern landmass that inclu- ded at least South America, Antarctica, and Australia and from there dispersed to North America and from there to Europe.

Acknowledgements

Funds for field work provided by grant 2467-82 from the National Geographic Society Washington, D.C. The field work was carried out under the auspices of I.B.B.A. (Insti- tuto Boliviano de Biologia de Altura) and the MISSION O.R.S.T.O.M. (Office de la Recherche Scientifique et Tech- nique Outre Mer). Field vehicles and other vital logistic support were provided by MISSION O.R.S.T.O.M. Support

for washing and sorting of matrix was provided by E.P.H.E. (Ecole Pratique des Hautes Etudes), Montpellier. The specimens were illustrated by Ariane Beaux (Montpel- lier). We thank Leonard Ginsburg, Robert Hoffstetter, Zofia Kielan-Jaworowska, and Donald E. Russell for comments of the manuscript.

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REFERENCES

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Manuscr i t d6fini t i f requ le 19.10.1983

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Late Cretaceous mammals (Marsupialia) from Bolivia