Journal of Vertebrate Paleontology 16(2) :292 -296, June 1996 © 1996 by the Society of Vertebrate Paleontology A NEW EARLY EOCENE POLYDOLOPIMORPHIAN (MAMMALIA, MARSUPIALIA) FROM PATAGONIA FRANCISCO J. GOIN,I and ADRIANA M. CANDELN 'Departamento Paleontologia Vertebrados and 2C itedra de Anatomia Comparada, Museo de Ciencias Naturales de La Plata, Paseo del Bosque sin, 1900 La Plata, Argentina ABSTRACT-We describe Rosendolops primigenium gen . et sp. nov (Mammalia, Marsupialia, Polydolopimorphia), based on isolated upper molars found in early Eocene (Casamayoran Age) beds from the cliffs south of Lake Col hue- Huapi (Province of Chubut, Argentina). The molar pattern shown by Rosendolops primigenium is clearly anticipatory of the characteristic polydolopimorphian (i.e., Prepidolopidae, Bonapartheriidae, and Polydolopidae) pattern, although the synapomorphies typical of the group are already present. Reigia punae and the Protodidelphidae (sensu Marshall, Case and Woodburne, 1990) are excluded from the Polydolopimorphia as they lack these synapomorphies. The mor- photype represented by Rosendolops primigenium sheds new light on the possible progressive modifications that enabled the establishment of the molar pattern in South American "pseudodiprotodont" marsupials. INTRODUCTION The first species of the Polydolopidae (Marsupialia, Poly- dolopimorphia) were described almost a century ago (Amegh- ino, 1897) from sediments exposed along the southern cliffs of Lake Colhue-Huapi, in central Patagonia, Argentina. Since then, a surprising variety of taxa referable to this family has been described (see a review in Marshall, 1982). All of them come from southern South America and Antarctica (Marshall, 1982; Woodburne and Zinsmeister, 1984; Case et al., 1988) . In the early 1980s, Pascual (1980, 1981a, b) published "New and unique ecological types of extinct marsupials" from early Eo- cene (Casamayoran Age) beds in northwestern Argentina. Sub- sequently, two new Paleogene families of marsupials were rec- ognized, Prepidolopidae and Bonapartheriidae. Their affinities seem to lie (with some reserve) with the Polydolopidae (see Pascual 1980, 1981a; Marshall, 1987; Aplin and Archer, 1987; Marshall et a!. 1990). More recently, Marshall et a!. (1990; see also Archer , 1984) proposed the Order Polydolopimorphia, ac- knowledging the monophyly of this group, as well as the com- plex diversity of the organisms represented in it. They included the families Prepidolopidae (including Reigia punae), Bona- partheriidae, Polydolopidae, and Protodidelphidae (but see be- low). The Prepidolopidae, Bonapartheriidae, and Polydolopidae were strictly Paleogene marsupials that developed a dental mor- phology compatible with frugivorous-insectivorous feeding habits (Pascual, 1980). They display a variable degree of "pseu- dodiprotodontisrn" (sensu Ride, 1964), the hypertrophy of the last premolars (especially the lower ones), and the development of brachyodont molars with poorly developed crests and low, rounded cusps. Of special interest is the pattern shown by the upper molars in each group. Successive stages in the evolution of this pattern may be represented among included taxa (Pas- cual, 1981b). In his review of the South American marsupials of the "beginning of the Age of Mammals, " Simpson (1948: 38) included specimen AMNH 28928 (an isolated upper molar) in the hypodigm of Caroloameghinia tenuis without further comment. However , this tooth is significantly different from the holotype of Caroloameghinia tenuis and from any other known caroloameghiniid (see below) . A new Casamayoran specimen from the southern cliffs of Lake Colhue-Huapi and housed in the collections of the Museum of La Plata (MLP-77-VI-14-3), is labeled "Caroloarneghiniidae indet." (see Pascual, 1981b). This specimen is essentially identical to AMNH 28928, al- though better preserved. We refer these two specimens to a new species and conclude that : I) the affinities of the new taxon lie with the Prepidolopidae, Bonapartheriidae, and Polydolopidae, with which it constitutes a monophyletic group , recognized here as Polydolopimorphia, and 2) the molar structure of specimens AMNH 28928 and MLP 77-VI-14-3 show the initial phases of the evolution of the polydolopimorphian molar pattern. Abbreviations for institutions and dental terminology: AMNH, American Museum of Natural History, New York ; MLp, Departamento Cientifico Paleontologia Vertebrados, Mu- seo de Ciencias Naturales de La Plata; P, upper premolar; M, upper molar . Molar notation for the adult dental formula of marsupials follows that of Goin (1991, 1995), that is, M I, M2, M3 and M4 . SYSTEMATIC PALEONTOLOGY Supercohort MARSUPIALIA IIliger, 1811 Order POLYDOLOPIMORPHIA (Arneghino, 1897) Family ?PREPIDOLOPIDAE Pascual, 1981a Genus ROSENDOLOPS gen . nov . Etymology-After Rosendo Pascual, paleontologist of the Museum of La Plata. He is the author of many of the studies carried out on the phylogeny of the Polydolopimorphia. His suggestions gave rise to many of the ideas presented in this paper . Type Species--Rosendolops primigenium, sp. nov. Diagnosis-As for the species, by monotypy. ROSENDOLOPS PRIMIGENlUM sp. nov. (Figs. I a-d, 2) Etymology-Alluding to the more generalized molar pattern of the type specimen, in the context of the Polydolopimorphia. Holotype-MLP 77-VI-14-3, an isolated right upper molar (?M2) without roots. Distribution-Southern cliff of Lake Colhue-Huapi, Chubut, Argentina ; Casamayoran Age (early Eocene). Collected by Ms. Hebe Herrera in I 977 . Hypodigm-The holotype and specimen AMNH 28928, an isolated right upper molar ( ?Ml) . Measurements--See Figure 2. 292 Downloaded by [UZH Hauptbibliothek / Zentralbibliothek Zürich] at 14:48 04 July 2014