New metatherian mammal from early Eocene levels of the la Meseta Formation, Antarctic Peninsula.

REGUERO, MARCELO; CHORNOGUBSKY, LAURA; ABELLO, M.A.; GOIN, F. J.; GELFO, JAVIER N.

Kuala Lumpur

Congreso; XXXIV Scientific Committee on Antarctic Research Meeting; 2016

We describe a new mammal coming from site IAA 1/90, Marambio (Seymour) Island, Antarctic Peninsula. The specimen (MLP 14-I-10-20) is a tiny lower left molar partially worn (total length: 2.24 mm; trigonid length: 0,72 mm; trigonid width: 1.11 mm; talonid width: 1.45 mm), and represents a new taxon for the Antarctic Paleogene mammalian assemblage. It was recovered from early Eocene (Ypresian) levels of the Cucullaea 1 Allomember, La Meseta Formation. Main features of it are its small size, brachydont and bunoid aspect, short trigonid, very wide and long talonid, closely set paraconid and metaconid, low protoconid, very large entoconid, the development of an incipient, bulbous cingulum at the labial base of the crown (between trigonid and talonid), and the persistence of a short posterior cingulum. The new specimen can be confidently referred to the Metatheria (Mammalia), more precisely to the Marsupialia. Within the latter, some features are reminiscent of the Paucituberculata (e.g., appressed para-and metaconid, quite developed and salient hypoconid, large entoconid). However, other features suggest the allocation of this specimen to basal polydolopimorphians, either stem Bonapartheriiformes (e.g., Prepidolopidae) or even to the more generalized Glasbiidae. Glasbids have been regarded as the basalmost clade within the whole order Polydolopimorphia, which is considered as part of the Australidelphia (i.e, Microbiotheria + Austalasian marsupials). The discovery of specimen MLP 14-I-10-20 offers new insights on the origins and early diversification of Australidelphian marsupials in southern continents. It also adds significant information to our knowledge of the diversity of Antarctic Paleogene mammals, their evolution and historical biogeography.