View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by SEDICI - Repositorio de la UNLP [Palaeontology, Vol. 50, Part 5, 2007, pp. 1267-1276] A NEW GENERALIZED PAUCITUBERCULATAN MARSUPIAL FROM THE OLIGOCENE OF BOLIVIA AND THE ORIGIN OF ‘SHREW-LIKE’ OPOSSUMS fry FRANCISCO J. GOIN*, MARCELO R. SÁNCHEZ-VILLAGRAf, ALEJANDRA ABELLO* and RICHARD F. KAYJ *División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina; e-mail: [email protected] ■¡■Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; current address: Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid Straße 4, CH-8006 Zürich, Switzerland; e-mail: [email protected] ^Department of Biological Anthropology and Anatomy, Duke University Medical Center, Box 3170, Durham, NC 27710, USA Typescript received 1 April 2006; accepted in revised form 26 October 2006 Abstract: Insights into the origin of ‘shrew-like’ oposssums lysis including representatives of the Caenolestidae, Pichipilus of South America are gained thanks to a new fossil from the and allies (not regarded here as caenolestids), Palaeothentidae, Oligocene Salla Beds in Bolivia. The specimen described here and Abderitidae, with three outgroups. Evolestes is the basal- consists of a partial rostrum, palate and postcanine teeth, and most ‘caenolestoid’, and provides clues to the morphological shows several generalized features (cranial and dental) in the changes involved in the origin of caenolestids. context of the Paucituberculata. On this basis we recognize Evolestes hadrommatos gen. et sp. nov. In order to evaluate the Key words: Metatheria, Marsupialia, Caenolestidae, Abde­ affinities of the new taxon, we performed a phylogenetic ana- ritidae, Palaeothentidae, South America, anatomy. Most of the fossil record of paucituberculatan marsupi­ fossil provides important information for reconstructing als consists of highly derived forms that illustrate the the last common ancestor of the Paucituberculata, the sis­ great extent of ecomorphological diversity attained by this ter group to the Australidelphia. The stratigraphical distri­ clade in the Cenozoic of South America (Bown and Flea­ bution of the genera considered in the phylogenetic gle 1993; Rae et al. 1996; Goin et al. 2003). Such richness analysis conducted in this study, and mentioned in com­ contrasts with the diversity and distribution of living pau- parisons, is listed in Table 1. Molar nomenclature follows cituberculatans (Caenolestidae), of which two or three Goin et al. (2003). The generalized metatherian dental genera and a handful of species of restricted Andean dis­ formula is assumed to be: I/i 5/4, C/c 1/1, P/p 3/3, M/m tribution exist (Bublitz 1987). These are the ‘shrew-like’ 4/4. The new specimen is housed in the Museo Nacional opossums, so-called because of their small size and insect- de Historia Natural, La Paz, Bolivia (MNHN-Bol). ivorous-faunivorous habits. The position of Caenolestidae in marsupial phylogeny has been a matter of long debate (Kirsch et al. 1997), but there is a growing consensus that SYSTEMATIC PALAEONTOLOGY they represent a clade second to South American opos­ sums (didelphids) in a pectinate phylogeny, being the sis­ MARSUPIALIA liliger, 1811 ter group to the diverse australidelphian radiation. This PAUCITUBERCULATA Ameghino, 1894 consensus is supported by both morphological (Horovitz and Sanchez-Villagra 2003) and molecular data (Amrine- Genus EVOLESTES gen. nov. Madsen et al. 2003; Nilsson et al. 2004; Phillips et al. 2006), as well as by combined analyses of the two (Asher Derivation of name. Evo, referring to evolution, because of the et al. 2004). importance of this fossil in showing the morphological changes Here we describe a fossil representing a new genus and involving the origin of a marsupial clade; Latin, lestes, thief, species of a ‘caenolestoid’, which provides insights into the pirate and, by extension, carnivorous (Greek, lestikos), a term that characterizes the generic name of several fossil and living phylogeny of the group and the origin of some of the mor­ Paucituberculata. phological specializations of shrew-like opossums. This © The Palaeontological Association doi: 10.1111/j.1475-4983.2007.00706.x 1267 1268 PALAEONTOLOGY, VOLUME 50 TABLE 1. Stratigraphical distribution of the genera considered in the phylogenetic analysis conducted in this study and mentioned in comparisons. Taxon Age Reference Turgidodon Lancian NALMA (Late Cretaceous) Case et al. (2005) Pucadelphys Tiupampan SALMA (Early Palaeocene) Muizon (1991) Derorhyncus Itaboraian SALMA (Late Palaeocene) Marshall (1987) Stilotherium Santacrucian SALMA (Middle Miocene) Marshall (1980) Pliolestes Montehermosan SALMA (Early Pliocene) Marshall (1980) Pichipilus Colhuehuapian-Santacrucian SALMA Marshall (1980) Phonocdromus Colhuehuapian-Santacrucian SALMA Marshall (1980) Palaeothentes Colhuehuapian-Santacrucian SALMA Bown and Fleagle (1993) Acdestis Santacrucian SALMA Marshall (1980) Abderites Colhuehuapian-Santacrucian SALMA Marshall (1980) Rhyncholestes Recent Patterson and Gallardo (1987) Lestoros Recent Marshall (1977) Caenolestes Recent Bublitz (1987) Type species. Evolestes hadrommatos sp. nov. Length M1-M3, 5-06 Length M1-M4, 5-98* Diagnosis. As for the type and only known species. Length Ml, 1-84 Width Ml, 1-72* Length M2, 1-95 Width M2, 2-12 Evolestes hadrommatos sp. nov. Length M3, 1-19 Text-figures 1-3 Width M3, 1-71 Length P3, 1-75 Derivation of name. Greek, hadros, well developed, strong, and Width P3, 0-62 ommatos, eye, implying that the type species has larger orbits Length P2 (alveolus), 1-54* than those of living caenolestids. Length Pl (alveolus), 0-97* Type. MNHN-Bol 96-400, a fragment of a skull preserving part Diagnosis. Differs from all other Paucituberculata in that of the rostrum, palate and skull roof; on the left side alveoli and the upper molars have a less-developed, ‘hypocone-like’ roots of the canine of Pl and of M4, fragmentary P2-M1 and metaconule. Differs from the Caenolestidae in having a complete M2-3; alveoli and roots of the right C-Pl (Text­ figs 1-2). shorter rostrum, larger orbits that are more dorsally placed; upper molars have a well-developed postmetacri- Hypodigm. The type only. sta, smaller stylar cusp D (StD), and the paracone and metacone are proportionally less coupled to stylar cusp B Occurrence. Salla Beds, an alluvial fill of a basin cut into (StB) and stylar cusp D (StD), respectively. Differs from deformed Palaeozoic strata at the edge of the eastern Andean the Pichipilinae in that the nasals end more anteriorly; in Cordillera of northern Bolivia (Sempere et al. 1990); stratigra­ pichipilines the protocone and metaconule are placed phic level 6 at Tapial Pampa. Kay et al. (1995) reported more posteriorly in relation to StB and StD, making the Ar40/Ar39 dates bracketing stratigraphic levels 5 and 6 at molar more quadrangular in occlusal view. The metacone between 24-93 ± 0-50 and 24-79 ± 0-27 Ma (late Oligocene), in Evolestes is twinned with StD whereas in pichipilines confirming previous age estimates of MacFadden et al. (1985) (and some caenolestines) the metacone has moved anteri­ and Naeser et al. (1987). orly with respect to the stylar region. Ml-2 of pichipilins have the occlusal surface of the metaconule proportionally Measurements (in mm); * = estimated value. Maximum width of nasals, 5-23* smaller in relation to that of the whole tooth than in Evo­ Skull height at the level of M3, 4-81 lestes. Differs from Palaeothentidae and Abderitidae in the Rostral width at the level of canines, 4-47 anterior extension of the maxillary fenestrae (in palaeo- Rostral width at the level of M3, 9-53 thentids the maxillary fenestrae of the palatal process of Palatal width at the level of M3, 5-10* the maxilla end anteriorly at the level of Ml whereas in Length of the left maxillary fenestra, 5-44 Evolestes they do this at the level of P2; Abderitidae lack Width of the left maxillary fenestra, 0-86 maxillary fenestrae); P3 is labiolingually compressed (not Length C-M3, 11-54 GOIN ET AL.: ORIGIN OF ‘SHREW-LIKE’ POSSUMS 1269 reaching the posterior widening typical of palaeothentids oblique, i.e. more frontal. As can be seen on the left side of the and abderitids); Ml-2 have the occlusal surface of the skull, the anterior border of the orbit is not round, forming metaconule barely above the occlusal surface of the trigon instead a crest at an angle of almost 90 degrees with the distal (in palaeothentids and abderitids the metaconule surface portion of the jugal bone. In the vertix of this angle at least a single lacrimal foramen can be seen, internal to the orbit. is relatively higher); StB and StD are less labiolingually The nasals are relatively narrow in their anterior portion compressed. and have subparallel lateral borders. Starting at the maxillary constriction, the nasals expand laterally, reaching their maxi­ Description mum width at the level of the Ml. Posterior to this point, the nasals join in the middle of the dorsal skull at the level Skull. Evolestes is slightly larger and more robust than Caeno- just behind the anterior border of the orbits. They expand in lestes fuliginosus. The rostrum was long, although shorter than in the skull roof more than in any other known Paucituberculata. living caenolestids, and narrow in its anterior portion. There is a The suture between the nasal and the maxilla is more or less marked constriction in the lateral expansion of the maxilla, just round in its anterior portion. Dorsally, the contact between the anterior to the level of P2. Posterior to this point, the rostrum frontal and the lacrimal is parallel to the sagital plane of the expands laterally. Orbits are relatively large and their upper bor­ skull. ders are not parallel to the sagittal plane but instead slightly The frontal-maxilla contact is wide, much wider than in the Didelphimorphia and similar to that of other Paucituberculata.