The diversity of bunodont ungulates during the early Eocene in Central – Western Patagonia, Argentina

GELFO J. N.; TEJEDOR M. F.

Austin, Texas, USA

Congreso; 67th Annual Meeting of the Society of Vertebrate Paleontology; 2007

Society of Vertebrate Paleontology

An outstanding diversity of mammals, including South American ungulates, marsupials, bats, and xenarthrans has been revealed from the localities of Laguna Fría and La Barda, the westernmost Paleogene mammal-bearing sites in Patagonia, Argentina. Located in northwestern Chubut Province, near the town of Paso del Sapo, these outcrops have 40Ar/39Ar dates taken from volcanic deposits underlying and overlying the mammal-bearing levels. Both faunas are late-early Eocene (Ypresian-Lutetian boundary), with an age ranging from 49.51 ± 0.32 Ma to 47.89 ± 1.21 Ma. The diversity and pecularity of the mammalian fauna from this area is biochronologically important  and pertinent to a better understanding of the South American Land Mammal Ages (SALMAs). During the Paleogene, bunodont South American ungulates were limited to the scarce diversity of the  Protolipternidae litopterns, the “condylarths” Mioclaenidae, and the endemic Didolodontidae. The bunodont ungulates from Paso del Sapo are small in body size.  They include at least two new didolodontids and the most abundant record of Asmithwoodwardia subtrigona (?Protolipternidae). One new genus is represented by a left mandibular fragment with m3 (LIEB-PV 1611). Unlike in other didolodontids, the entoconid presents a low cristid reaching the hypoconid distally. The second new genus is based on a right mandible with part of the talonid of m2 and complete m3 (LIEB-PV 1612). The major diagnostic character is the presence of a huge entoconid larger than the hypoconid, almost closing the talonid basin. In contrast to Asmithwoodwardia scotti from the Itaboraian SALMA (late Paleocene-early Eocene), A. subtrigona from Paso del Sapo is larger and has postparaconular and premetaconular cristae; the M3 is not so transversally elongated, and the postcingulum lingually ends in a small hypocone. The inferred subtropical, moderately seasonal climate of these mammalian assemblages toward the end of the Early Eocene Climatic Optimum in some ways is transitional between the mammalian records of previous and later SALMAs.