From the Early Miocene of Patagonian Argentina

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln

USGS Staff -- Published Research US Geological Survey

1996

New Palaeothentid Marsupials (Caenolestoidea) from the Early Miocene of Patagonian Argentina

Todd C. Rae American Museum of Natural History

Thomas M. Bown U.S. Geological Survey

John G. Fleagle State University of New York at Stony Brook

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Rae, Todd C.; Bown, Thomas M.; and Fleagle, John G., "New Palaeothentid Marsupials (Caenolestoidea) from the Early Miocene of Patagonian Argentina" (1996). USGS Staff -- Published Research. 198. https://digitalcommons.unl.edu/usgsstaffpub/198

This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- Published Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. AMERICAN MUSEUM Novtates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3 165, 10 pp., 10 figures April 11, 1996

New Palaeothentid Marsupials (Caenolestoidea) from the Early Miocene of Patagonian Argentina

TODD C. RAE,I THOMAS M. BOWN,2 AND JOHN G. FLEAGLE3

ABSTRACT Recent fieldwork in Argentina has resulted in these is the length of the ml paracristid, which is the recovery of numerous new specimens of pa- nearly twice the size of that seen in the largest laeothentid marsupials, an important component palaeothentine known previously (Palaeothentes of the Deseadan-Santacrucian (Oligocene-middle aratae). Details ofthe molar structure indicate that Miocene) mammalian fauna of Patagonia. The the phylogenetic affinities of the new form prob- 1994 collections include a new genus and species ably lie with P. aratae and P. primus. from the early Miocene Pinturas Formation at Es- The new dentary ofAcdestis contains the com- tancia La Cafnada and the first complete lower den- plete lower dentition, including many previously tition ofAcdestis oweni from a locality in the Santa unknown anterior teeth. This specimen confirms Cruz Formation along the Rio Chalia. that the lower dental formula ofA. oweni is 2.1.3.4. Specimens from the La Cafiada locality, an iso- The central incisor is large and procumbent. The lated ml and two dentary fragments, represent a previously unknown i2-p2 are minute, single-root- new genus and species of a very large palaeothen- ed, and resemble those ofother palaeothentids and tine, here named Titanothentes simpsoni, new ge- even abderitids in having an elongated mesial ex- nus and species. Several dental features distinguish tension of the enamel, giving the teeth a "bent" the new form from its closest relatives. Chiefamong appearance in lateral view.

' Research Associate, Department of Mammalogy, American Museum of Natural History; Lecturer, Department of Anthropology, University of Durham, 43 Old Elvet, Durham, DHl 3HN, England. 2 Senior Paleontologist, U.S. Geological Survey, Box 25046, Mail Stop 919, Denver Federal Center, Denver, CO 80225, USA. 3Professor, Department of Anatomical Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.

INTRODUCTION Palaeothentid marsupials have been known maining palaeothentids. Collections made in from Tertiary deposits in South America since 1994 include several new specimens that shed the 19th century (Ameghino, 1887). Remains additional light on this unusual group ofsmall of this extinct family of small caenolestoids, fossil marsupials (Rae et al., 1994). In this related to extant rat opossums, occur in Oli- communication we report the first complete gocene through Miocene rocks from Colom- dentition ofAcdestis oweni and a new genus bia to the southern portion of mainland Ar- and species of palaeothentid from central gentina (Marshall, 1980; Bown and Fleagle, Santa Cruz Province, Argentina. 1993; Dumont and Bown, in press). The family Palaeothentidae was recently revised by ACKNOWLEDGMENTS Bown and Fleagle (1993) on the basis ofhun- The authors take this opportunity to thank dreds ofnew specimens recovered since 1982. the staffs of the Museo Argentino Ciencias The authors recognized 9 genera and 19 spe- Naturales "Bernardino Rivadavia," Buenos cies ofpalaeothentids, contained primarily in Aires (MACN) and Central Patagonian Re- two subfamilies, the Palaeothentinae and the search Center, Puerto Madryn (CENPAT), Acdestinae. The new late Miocene form from and the 1994 field crew: Silvia Cornero, Ma- Colombia (Dumont and Bown, in press) is ria Teresa Dozo, Mario Cozzuol, Ines Ho- considered a separate lineage from the re- rovitz, Analea Forasiepi, Alejandro Kra- martz, Marcelo Tejador, Robert Taylor, and Jorge Upton. The photos were prepared by C. Tarka, the scanning electron micrographs by P. Melville, and figure 4b by E. Brothers. We thank Ken Rose and Betsy Dumont for critical comments on an earlier draft of this paper. This research was supported by a Kalbfleisch Research Fellowship from the American Museum of Natural History to TCR, and National Science Foundation grant BNS 9012154 to JGF. SYSTEMATIC PALEONTOLOGY SUPERORDER MARSUPIALIA ILLIGER, 1811 ORDER PAUCITUBERCULATA AMEGHINO, 1894 FAMILY PALAEOTHENTIDAE (SINCLAIR, 1906) OSGOOD, 1921 SUBFAMILY PALAEOTHENTINAE SINCLAIR, 1906 Titanothentes, new genus w f t G = TYPE SPECIES: Titanothentes simpsoni, new ~~~~~~~. and only known species. Fig. 1. Geographic position of La Caiiada and ETYMOLOGY: Greek titan-, of enormous Rio Chalia (*). Collections were made by an in- ternational team from the State University ofNew size, strength, power; and ?Tehuelche -thentes York at Stony Brook, U.S. Geological Survey, (see Marshall, 1980, for a discussion of the American Museum ofNatural History, Museo Ar- possible etymology), a common suffix for pa- gentino Ciencias Naturales "Bernardino Rivada- laeothentids. via," and Central Patagonian Research Center. TYPE LOCALITY: Estancia La Caniada, cen- 1 996 RAE ET AL.: PALAEOTHENID MARSUPIALS FROM ARGENTINA 3

a b

I~~~~~~~~~~~ Fig. 2. (a) Stereopair (occlusal view) of the holotype of Titanothentes simpsoni (MACN SC-3 1 57a), a left dentary with ml -2. Note especially the elongated paracnstid of ml. (b) Stereopair (occlusal view) of MACN SC-3 156 (T. simpsoni), a right dentary with m2. In this and all subsequent photographs, the scale bar = 5 mm. tral Santa Cruz Province, Argentina. The ge- stratigraphic position similar to that at Cauce ology and stratigraphy of the Miocene pa- Seca in the upper-middle Pinturas Formation laeothentid sites in southern Argentina are of the Rio Pinturas area further north (Bown summarized in Bown and Larriestra (1990) and Fleagle, 1993). and Bown and Fleagle (1993). This site is DIAGNOSIS: Largest known palaeothentine, located in north-central Santa Cruz Province, ml about 25% longer MD (mesiodistally) than southern Argentina, between the Rio Dese- mean of ml in Palaeothentes aratae. Differs ado to the north and the Rio Chico to the from all palaeothentids in having a very short south (47°58.85'S latitude, 70°09.81'W lon- ml talonid, an extremely long ml paracris- gitude: see fig. 1). The outcrop is a small am- tid, and a pronounced size discrepancy be- phitheater about 4.5 km north ofthe estancia tween ml and m2; differs from palaeothen- house. Fossils occur in a paleosol developed tids other than P. aratae and P. primus in on an erosion surface that bordered a small having an anterior extension (or mure) on the lake or pond. Paleosol development and the entoconid of ml; differs from palaeothentids erosional unconformity at the site indicate a other than,P. aratae, P. primus, P. boliviensis, 4 AMERICAN MUSEUM NOVITATES NO. 3165

I a b

Fig. 3. Dentaries of T. simpsoni (lateral view). (a) MACN SC-3157a (holotype); (b) MACN SC-3156. and Carlothentes in possessing a shallowly middle Miocene); Estancia La Caiiada, Pro- bifurcated ml paraconid. vincia de Santa Cruz, Argentina. ETYMOLOGY: Named for G. G. Simpson, a pioneer in South American paleontology. Titanothentes simpsoni, new species DISCUSSION: Titanothentes simpsoni is among the largest species of palaeothentids, HOLOTYPE: MACN SC-31 57a, left dentary equaling the size ofthe largest palaeothentine with ml-2 and alveoli of pl-3 and m3 (figs. species known previously (P. aratae) in the 2a, 3a). depth of the corpus and exceeding all other DIAGNOSIS: Only known species; as for ge- palaeothentines in ml MD length. Only the nus. dentary and lower first and second molars of HYPODIGM: The holotype; a right dentary the taxon are known (two examples of each). with m2 and alveolus of ml (MACN SC- Both the holotype (fig. 2a) and MACN SC- 3156; figs. 2b and 3b); and an isolated right 3156 (fig. 2b) preserve portions of the den- ml (MACN SC-1613; fig. 4). tary. The holotype is a fragmentary left den- DISTRIBUTION: Upper part of the middle tary, broken through the alveoli for p1 an- Pinturas Formation; Santacrucian (early- teriorly and m3 posteriorly. The corpus of 1 996 RAE ET AL.: PALAEOTHENID MARSUPIALS FROM ARGENTINA 5 a b Shallowsrn

h -

Elongated ' paracristid

P.I. .

Entoconid . mure I I Fig. 4. MACN SC- 1613 (Titanothentes simpsoni), a right ml. (a) Stereopair (occlusal view) of specimen; (b) schematic drawing (not to scale) with the major characteristics highlighted.

SC-3156 is nearly identical in preservation, is a mental foramen below ml that is situated although it is broken anteriorly through the just superior to midcorpus. There are two alveolus of p2. The corpus of Titanothentes additional foramina in the holotype (one in is relatively deep and gracile (fig. 3a, b). There SC-3 156) that lie beneath the alveolus of p2

* Titanothentes 2.4F * Propalaeothentes # R minutus U * P 1.9 F marshalli + A Carlothentes 01% * R pascuali 2 1.4 * V o P lemoinei X E R primus v Pilchenia 0.9 0 e P interrnedius + P aratae

r1 P migueli 0.4' I I I I I I 0.4 0.6 0.8 1 1.2 1.4 1.6 In(m2 MD length) Fig. 5. Natural log (ln) of MD length for ml plotted against (ln) MD length of m2 for palaeothentids. Titanothentes (filled square) possesses an ml that is longer than that of any other known palaeothentid. 6 AMERICAN MUSEUM NOVITATES NO. 3165 and open anteriorly. The lower of the two foramina is about half the size of the upper and is situated at midcorpus. An alveolus for b a large, procumbent incisor is clearly visible at the inferior margin of the mesial break in both specimens. The inferior and superior margins of the dentary are parallel under the molar teeth, but the corpus becomes shallower under the premolars (fig. 3) as in some other palaeothentids (see fig. 10). Both the first and second lower molars are represented, but one specimen ofml and both specimens of m2 are heavily worn. SC- 1613 (an isolated m 1) is relatively unworn, but the distal portion ofthe talonid is missing; a shallow bifurcation of the paraconid can be seen clearly (fig. 4). There is a mure, or anterior shelflike extension (Bown and Fleagle, 1993; see fig. 4b), on the entoconid. The first molar also possesses a trigonid on which the metaconid is twinned into a large talonid moiety and much smaller trigonid moiety (trigonid pattern 4 of Bown and Fleagle, 1993). The first lower molar in Titanothentes is extremely long mesiodistally. Even though it is severely worn in SC-3 1 57a, the ml of this specimen is, in fact, longer than all other palaeothentid mls (fig. 5). In addition to possessing a long ml, Titanothentes also has a uniquely elongated ml paracristid, nearly twice the size of that seen in any other palaeothentid (fig. 6). The great length of this tooth may not be attributable to larger overall body size in Titanothentes, as the m2 of the new genus is shorter mesiodistally than in some other palaeothentids (see fig. 5) and the Fig. 6. Titanothentes compared to the largest depth of the dentary at ml is indistinguish- previously known palaeothentid, Palaeothentes able from that in P. aratae, formerly the larg- aratae. (a) Holotype of T. simpsoni (MACN SC- est known member of the Palaeothentinae 31 57a); (b) right dentary ofP. aratae (MACN SC- (fig. 7). 1302: image reversed) in occlusal view. Note in- The m2 is broad, short, and heavily worn creased MD length of m 1 and relative elongation in both the holotype and SC-3 156. Measure- of ml paracristid in T. simpsoni. ments ofthe holotype indicate that this tooth is smaller than the average m2 of P. aratae thentines (fig. 8). It is possible that some por- in terms of mesiodistal (MD) length (see fig. tion of the reduced length of m2 in the ho- 5), although the buccolingual (BL) width of lotype may be an artifact of damage (a small the tooth is exceeded by only two specimens portion ofthe distolingual margin ofthe tooth of P. aratae. The ratio of ml /m2 MD length enamel is missing) or of interstitial wear in T. simpsoni is also unique among palaeo- against ml, which appears to be advanced. thentids, as ml is 195% the MD length of There is, however, interstitial wear on ml as m2. This value falls well outside the range of well, which suggests that the ml/m2 ratio the ml/m2 length ratio for all other palaeo- reported probably corresponds closely to the 1 996 RAE ET AL.: PALAEOTHENID MARSUPIALS FROM ARGENTINA 7

I I I

Fig. 7. Titanothentes compared to the largest previously known palaeothentid, Palaeothentes aratae. (a) T. simpsoni (MACN SC-3157a); (b) P. aratae (MACN SC-1302: image reversed) in lateral view. These taxa are indistinguishable in the depth of the corpus below ml. value that would be expected ifthe specimens polarities ofBown and Fleagle (1993) and the were unworn. maximum parsimony algorithm of the com- T. simpsoni shares several characters with puter program Hennig86 (Farris, 1988), con- other palaeothentines. In particular, the shal- firms this arrangement and suggests that P. lowly bifurcated paraconid and the entoconid aratae, P. primus, and T. simpsoni are the mure are seen primarily in P. aratae and P. most derived ofthe palaeothentines. The data primus. Bown and Fleagle (1993) proposed at hand are not sufficient, however, to resolve that these characteristics ofml link P. aratae the trichotomy between these three species and P. primus deep within the palaeothentine and additional data are needed to clarify the clade. Phylogenetic analysis ofPalaeothentes phylogenetic relationships within this clade and Titanothentes, using the characters and of advanced palaeothentids. 8 AMERICAN MUSEUM NOVITATES NO. 3165

Pr. hatcher/ * 70°06.21'W longitude; see fig. 1), south of Estancia La Ensenada. This site is located in Pa. minuLts rT' extensive exposures of the Santa Cruz For- Pr. lspidus H+ mation that are developed along the south Pa. pascull side ofthe Rio Chalia, south ofLaguna Gran- de and about 125 km northwest ofCmte. Luis Pa. migueli Piedrabuena. These exposures almost cer- Pa. intedius tainly include the "Sehuen" locality de- PaL lmoinei H|I-H scribed by Ameghino (1891) and Hatcher (1903). 94d-2 is in the basal Santa Cruz For- Pa. aratue | mation, about 50 m above the local contact Cwdomentes * with marine rocks of the underlying Grupo Plichenna Patagonia. DESCRIPTION: The new specimen ofthe ac- Pa. primus ' destine Acdestis oweni is a nearly complete Pa. m larh/ * left dentary with complete dentition (fig. 9). Tkanomnts * This is the first known specimen of the species with associated anterior and posterior .1 1.3 1.5 1.7 1.9 teeth. The corpus is complete anteriorly; poste- ml / m2 MD length riorly it is broken obliquely from the anterior Fig. 8. Ra*tio of ml MD length over m2 MD root ofthe ramus inferiorly to the base ofthe length in pala eothentids. T. simpsoni falls outside corpus. There is a slight medial inflection of the range of all previously known taxa for this the base of the dentary. The corpus is rela- variable. tively shallow and gracile, but lies within the range of depth (5.43 mm) at ml ofA. oweni specimens known previously. The dentary is SUJBFAMILY ACDESTINAE uniformly deep under the molars, but is sig- BO,WN AND FLEAGLE, 1993 nificantly shallower anterior to p3. There is a mental foramen between the roots of ml Acdest isoweimegin,18at midcorpus and a second foramen between NEW MATPERiAL: MACN SC-3649, a left c and p1 that opens anteriorly. The symphy- dentary with complete dentition (fig. 9). seal surface is a nearly horizontal, oval struc- LocALITY: The specimen was collected from ture that is concave and rugose. Although it locality 94d-2 (49037.65'S latitude, is broken superiorly, it is clear that the root

Fig. 9. Scanning electron micrograph ofAcdestis oweni dentary MACN SC-3649 (lateral view). Note the unusual conformation of the crowns of il-p2. 1 996- RAE ET AL.: PALAEOTHENID MARSUPIALS FROM ARGENTINA 9

a C

b d Fig. 10. Mandibular dentition of A. oweni and other caenolestoids (lateral view: not to scale). (a) New specimen ofA. oweni (MACN SC-3649) showing the "bent" appearance of i2-p2; (b) A. oweni as originally reconstructed (the crowns of il-p2 were unknown); (c) Palaeothentes; (d) Abderites (Abderi- tidae). [b-d after Ameghino]

of the ascending ramus did not overlap the Fleagle, 1993). A single cusp is situated me- molar row in lateral view and that the ramus sially on the crown. There are two roots lin- was deeply excavated for the insertion of the gually, but they appear fused on the buccal masseter muscle. side; the alveolus is "figure 8-shaped" as in The central incisor is a large, procumbent MACN 2038 (Marshall, 1980). The cusp tip tooth. The bone is formed closely about the is slightly damaged. root, which can be seen (on the lingual surface The heavily worn molars, which decrease ofthe dentary) to extend posteriorly to below in size posteriorly, conform to the pattern ml. Most of the tip of the crown is missing, seen in all other acdestines; the paraconid is but it appears to have been bilaterally com- not bifurcated, and m2-4 are not constricted pressed. The anteriormost part of the re- in the region of the hypoflexid and talonid maining crown is smooth, as if from wear, notch as in many palaeothentines. The new and a small dentine island is exposed. More dentary closely resembles other specimens of posteriorly, the surface of the crown enamel A. oweni in its molar teeth. The ml displays is cracked. a trigonid pattern, found in 61% ofpreviously There are four teeth between the enlarged known specimens ofthe species, in which the incisor and p3. They are minute and single protocristid is more or less transversely rooted. On each, the enamel cap extends pos- aligned and the metaconid is not twinned teriorly down the root on the distal side, is (type 1 trigonid pattern of Bown and Fleagle, flat occlusally, and is elongated anteriorly, 1993). The m4 is greatly reduced (about the overlapping the root and giving the teeth a size of p3) and lacks cusp definition, another "bent" appearance in lateral view (figs. 9 and hallmark of the species. 1 Oa). The tooth nearest the incisor is the larg- DISCUSSION: This uniquely complete den- est and the tooth crowns decrease posteriorly tary provides answers to some lingering ques- in both size and in the degree of anterior tions about the dental morphology ofAcdestis extension. The anterior extension of each oweni. Initially, the anteriormost tooth ofA. tooth contacts the back of the crown of the oweni was reconstructed as a large, procum- next anterior tooth. bent incisor by Ameghino (1887; see fig.1Ob). The p3 in SC-3649 is a moderately tall, Indeed, the anterior incisor in the new spec- pointed tooth, closely approximated against imen is also large and procumbent, a con- the anteroinferior edge of ml. It resembles dition similar to that seen in other palaeo- the p3 in SC-972 (see fig. 13 of Bown and thentids from the Patagonian Miocene. 10 AMERICAN MUSEUM NOVITATES NO. 3165

The nature of the other antemolar teeth of small and implanted vertically (Bown and A. oweni was unclear previously. In the first Fleagle, 1993). illustrations ofthe species, Ameghino (1891) The new specimen contains four teeth be- reconstructed four teeth between the central tween i 1 and p3 and demonstrates that incisor and p3, with crowns that were low Ameghino's reconstruction of the shapes of and relatively flat (c-p2) or faintly caniniform the i2-p2 crowns was inaccurate. Rather than (i2: see fig. 1Ob). As more specimens were the flat or caniniform appearance hypothe- discovered, the number of teeth anterior to sized, these teeth have "bent" crowns when p3 (judged from alveoli) was shown to vary; seen in lateral views (figs. 9 and 1Oa). In fact, in at least three specimens that are complete their shape is similar to that seen in other between the p3 and the enlarged incisor, there palaeothentids and even abderitids (figs. 1 Oc, are only three alveoli in this area (Marshall, d). The antemolar teeth are also similar to 1980). Marshall (1980) hypothesized that p2 those seen in some living shrews and their was lost in these individuals, on the basis of shape may be related to insectivory, although a space between p3 and the alveolus of the the dietary pattern inferred forA. oweni, based next anterior tooth on one dentary (MACN on body weight and dental shearing crests, 5693) and a small depression in this area in also includes a high proportion offruit (Strait another (MACN 8254). The alveolus im- et al., 1 990; Bown and Fleagle, 1993). Further mediately posterior to the enlarged incisor of work, including microwear analysis, should some incomplete A. oweni dentaries (e.g., help to clarify the dietary preferences of this MACN SC-578 and SC-1473) had suggested interesting Miocene marsupial. that the "penultimate anterior" tooth was

REFERENCES Ameghino, F. lombia. In R. Kay, R. Cifelli, R. Mad- 1887. Enumeracion systematica de las espe- den, J. Flynn (eds.), The history of a cies de mammiferos f6siles coleccio- Neotropical fauna: vertebrate paleo- nados por Carlos Ameghino en los terr- biology ofthe Miocene oftropical South anos eocenos de la Patagonia austral y America. depositados en el Museo La Plata. Bole- Farris, J. S. tin Museo de La Plata 1: 1-26. 1988. Hennig86. Port Jefferson Station, NY: 1891. Nuevos restos de mamiferos fosiles des- distributed by the author. cubiertos por Carlos Ameghino en el Hatcher, J. B. Eoceno inferior de la Patagonia austral. 1903. Narrative of the expeditions and geog- Especies nuevas, adiciones y corre- raphy of southern Patagonia. Rept. ciones. Revista Argentina de Historia Princeton Univ. Exp. Patagonia 1: 1- Natural 1: 289-328. 314. Bown, T. M., and J. G. Fleagle Marshall, L. G. 1993. Systematics, biostratigraphy, and den- 1980. Systematics of the South American tal evolution of the palaeothentidae, marsupial family Caenolestidae. Field- Later Oligocene to Early-Middle Mio- iana (Geology), n.s., 5: 1-145. cene (Deseadan-Santacrucian) caeno- Rae, T. C., T. M. Bown, and J. G. Fleagle lestoid marsupials of South America. 1994. New palaeothentid marsupials from the Mem. Paleontol. Soc. 29: 1-76. Miocene of Patagonia. J. Vertebr. Pa- Bown, T. M., and C. N. Larriestra leontol. 14 (suppl. to no. 3): 43A. 1990. Sedimentary paleoenvironments offos- Strait, S. G., J. G. Fleagle, T. M. Bown, and E. R. sil platyrrhine localities, Miocene Pin- Dumont turas Formation, Santa Cruz Province, 1990. Diversity in body size and dietary habits Argentina. J. Hum. Evol. 19: 87-119. offossil caenolestid marsupials from the Dumont, E. R., and T. M. Bown Miocene of Argentina. J. Vertebr. Pa- In press. New caenolestoid marsupials from the leontol. 10 (suppl. to no. 3): 44A. La Venta Formation (Miocene) of Co-