EARLIEST PALEOCENE MARSUPIALS FROM PATAGONIA

GOIN, F. J.; FORASIEPI, A. M.; CANDELA A.; ORTIZ JAUREGUIZAR E.; PASCUAL R.; ARCHER M.; GODTHELP H.; MUIRHEAD J.; AUGEE M.; HAND S.; WROE S.

Sydney, Australia

Congreso; I International Palaeontologial Congress; 2002

Geological Society of Australia

The Paleocene fauna from Punta Peligro (Hansen Member, Salamanca Formation; Chubut Province, Argentina) is the oldest Cainozoic vertebrate association known from Patagonia. It includes a variety of vertebrates: several fish, pipid and leptodactilyd frogs, chelid turtles, crocodiles, and a unique combination of Gondwanan and Laurasian mammalian lineages: monotremes, gondwanatherians, dryolestoids, marsupials and placentals (Bonaparte et al., 1993; Gelfo & Pascual 2001). Field work carried out during the last decade in this area led to the recovery of the earliest Patagonian Cainozoic marsupials, as well as one of the oldest marsupial faunas from South America.   Punta Peligro marsupials. The Punta Peligro marsupials include the following. 1) A new species of the “opossum-like” marsupial Derorhynchus differs from the other species of the genus in its very small size and in that the lower molars have more mesially placed paraconids and shortened entocristids. 2) A new species of Didelphopsis differs from the type species of the genus in having upper molars with very large, prismatic-shaped stylar cusp C, deep trigon basin, and high, eccentric protocone. 3) A small, toothless dentary fragment, whose size does not match that of other marsupials from Punta Peligro, indicates that at least one more species of “opossum-like” marsupial was present in this fauna. 4) An isolated astragalus belonging to a fox-sized borhyaenoid constitutes the largest marsupial known from this fauna. 5) A new polydolopimorphian species is characterized by its large-basined lower molars, small but distinct paraconids and sligthly inflated anterobasal cingulids. 6) Finally, a second polydolopimorphian, representing a new genus and species of bonapartheriid, is presently being described elsewhere. The composition of this marsupial fauna indicates that, already by Peligran times, adaptive trends towards insectivory, carnivory, frugivory, and omnivory were established. Also, Peligran marsupials suggest that the origin and radiation of several South American lineages (especially, the polydolopimorphians) seem to have pre-dated the Cainozoic.   Comments on the age of Punta Peligro mammals. Three hypotheses have been postulated about the age of Punta Peligro Local Fauna (LF), particularly with respect to the Tiupampa LF of Bolivia: (1) both are contemporary (Danian; Pascual and Ortiz Jaureguizar, 1991); (2) the Tiupampa LF is older (although both Danian; Bonaparte et al., 1993); (3) the Punta Peligro LF is younger (earliest Selandian in age; Marshall et al., 1997). When marsupials of both faunas are compared, Tiupampan taxa are clearly more plesiomorphic than those of Punta Peligro. The Punta Peligro marsupial assemblage shares at least two genera (Derorhynchus and Didelphopsis) with younger (Itaboraian Age) marsupials from Itaboraí (Brazil) and Las Flores (Argentina). Despite this, similarity analyses among late Cretaceous/Paleocene South American mammal faunas suggest affinities between Punta Peligran mammals and those from older (Alamitian) assemblages, hence the absolute age of the Punta Peligro LF is unclear. If the ages of the Tiupampa and Punta Peligro LFs are similar, and this is not yet established, taxic differences between them would suggest some degree of isolation between Patagonia and the rest of the South American continent at that time, with relatively plesiomorphic taxa having been isolated in the more southern region of the continent. Palaeogeographic evidence supports the hypothesis that there could have been biogeographic barriers at least in the Paleocene enabling even contemporaneous assemblages to develop regional distinctions.