NEW NON-THERIAN MAMMAL FROM MARAMBIO (SEYMOUR) ISLAND IN WEST ANTARCTICA: FIRST MERIDIOLESTID OUTSIDE SOUTH AMERICA

MARTINELLI, A.G.; CHORNOGUBSKY, L.; ABELLO, M.A.; GOIN, F. J.; REGUERO, M.A.

Congreso; 4th International Paleontological Congress; 2014

The La Meseta Formation records ca. 20 ma of sedimentation (Early Eocene to ?early Oligocene) in the Marambio Island, Antarctic Peninsula. Its Cucullaea I Allomember contains most of the recorded mammal, including non-therian gondwanatheres, metatherians, and eutherians (Pilosa, Litopterna and Astrapotheria). This composition reflects a strong paleogeographical link between the Paleogene faunas of Patagonia and West Antarctica. A small isolated tooth (MLP-91-11-4-3) was found in locality IAA-1/90 from Cucullaea I Allomember and was originally interpreted as a possible third upper molar from a bat or an "insectivore" because of its zalambdodont appearance, and then more broadly assigned to Mammalia Incertae sedis. We present here an alternative interpretation, considering MLP-91-II-4-3 as a right lower molar of a non-therian Dryolestoidea, possibly being a member of the clade Meridiolestida. The crown is dominated by three cusps and a distolingual talonid cusp. The protoconid is flanked mesially by the paracristid and distally by the metacristid, which reach the paraconid and metaconid, respectively. Both crests form an acute angle, without a clear notch at mid-way. The labial wall of the protoconid is convex whereas the lingual face is slightly concave. The paraconid is worn out and lower than the metaconid. The flexid is notorious and forms a ?v? shaped notch between paraconid and metaconid. The protoconid and metaconid are similar in height. The metaconid connects by means of a crest with the talonid. The talonid has a hook-like disto-lingual projection with a large cusp, slightly bent lingually, and an accesory more labially placed cuspule. The mesial cingulum starts as a thin ridge below the paraconid and becomes wider on its ventrolabial trajectory. It is unknown if the cingulum continues on the labial slope of the protoconid. A portion of a root is preserved below the paraconid-protoconid and it seems to be transversely wide. The crown morphology of MLP-91-II-4-3 closely resembles that of the meridiolestidans Barberenia and Brandonia from the Late Cretaceous of Patagonia (Los Alamitos and Allen formations). Meridiolestida is a diverse group of dryolestoids recorded mostly from Patagonian Cretaceous outcrops, which survived the Cretaceous/Paleocene boundary with the youngest representative of the clade (Necrolestes) from early Miocene age. If proven correct, our hypothesis would expand the distribution of the Meridiolestida to West Antarctica, representing the second non-therian mammal from this continent. Thus, it would agree with previous inferred scenarios that show West Antarctic faunas as more closely related to those of the Paleogene of Patagonia than to any other one from the Southern Hemisphere.