THE OLDEST KNOWN (EARLY EOCENE) MAMMAL FROM ANTARCTICA

MÖRS, T.; GELFO, J.N.; REGUERO, M.A.; LORENTE, M.; LÓPEZ, G.M.

Ls Angeles

Simposio; 73 Annual Meeting SVP; 2013

Society of Vertebrate Paleontology

An isolated tooth and an intermediate phalanx of terrestrial mammals were exhumed in Seymour/Marambio Island from a basal marine horizon of the Acantilados Allomember (TELM 2) of the La Meseta Formation. The bearing horizon is stratigraphically lower than any other terrestrial mammal locality known in the unit. It is well exposed along the sea cliffs facing the López de Bertodano Bay and extends inland toward the east by its high mud content, a paucity of shell beds, and well‐preserved fine stratification. Small wood fragments are often concentrated in the muds or at thin ferruginous, concretionary seams. The depositional setting is interpreted to be an estuary and the microplankton, Sr86/Sr87 and paleomagnetic datations at the levels where the remains were recovered indicate an early Eocene age. So these two fossils represent the earliest records of terrestrial mammals from Antarctica. The tooth is a left talonid fragment of m2? without roots identified as Notiolofos cf. N. arquinotiensis (Litopterna: Sparnotheriodontidae). The labial side of the talonid shows a wrinkled surface not seen in the sharper lingual side. A large hypoconid fill the distolabial side as part of a lophid which continues mesially in the cristid obliqua. Hypoconulid is small and is connected to the entoconid by a faint postcristid. An ?entonconulid mesial to the entoconid probably close the talonid valley lingually. The talonid basin is not so wide but is particularly deep. The intermediate phalanx is wider than long. The processus extensorius is well marked and there are two tuberositas flexoria? on the palmar side below the articular fossae for the proximal phalanges. There are two dorsal foramina in the diaphysis, four foramina below the processus extensorius on the proximal left border (in proximal view). Considering the already known terrestrial mammals from Antarctica, the phalanx more closely resembles those present in Litopterna such as Megadolodus in its proportions, with a wider proximal epiphysis than the distal one. It also differs from astrapotherians like Astrapotherium since the only preserved intermediate phalanx is longer than wide. These new records highlight the importance of South American native ungulates in Paleogene Antarctic faunas, raising new questions about paleobiogeographic relations and the time of the break of the South America‐Antarctica land connection.