New eutherian mammal from the Eocene of La Meseta Formation, Seymour Island, Antarctica

GELFO J. N.; LÓPEZ, G. M; REGUERO, M.; BOND, M.

Auckland

Congreso; XXXIII SCAR Biennial Meetings; 2014

Antarctica New Zealand

The Antarctic fossil record of terrestrial mammals is restricted to Eocene times. It is represented by several lineages derived of those present in the Cretaceous and Paleogene of South America. This record includes Gondwanatheria, a wide diversity of ?opposum-like? metatherians and placental mammals represented by native ungulates (i.e. Astrapotheriidae, Sparnotheriodontidae). The presence of Xenarthrans and Insectivoran or Dryolestida, needs further confirmation. We report an eutherian left m2? fragment represented by the talonid (MLP 12-I-20-4), recovered from La Meseta Formation at the IAA 1/90 locality in Seymour Island. This small talonid (6.25 x 6.01 mm) shows a strong hypolophid?, with a large hypoconid filling the distolabial side, and a small hypoconulid, placed as the more distolingual cusp. The talonid basin is deep. An unworn bunoid and small entoconid is located mesial to the hypoconulid and related to it by a faint postcristid. The entoconid and the hypoconid are placed almost in the same transverse line. A small cusp? mesial to the entoconid seems to be close the talonid valley lingually. In the labial side, a narrow and slender cristid obliqua projects almost mesially. There is a small ?pocket? or rim present in the base of mesiolabial side and the ectoflexid is absent. The base of the labial side of the talonid shows a wrinkled surface not seen in the sharper lingual side. MLP 12-I-20-4 more resembles the morphology of some Sparnotheriodontidae for the position and development of the entoconid, than any other placental mammal. Even though, it differs from them, particularly of the Antarctic Notiolofos, for the labial pocket, the close talonid basin, absence of cingulids and ectoflexid, and different inclination of wear between the cristid obliqua and the hypolophid?. While the occurrence of non-therian mammals could be explained by vicariance or dispersal events, therian mammals fit well with a dispersion model related to the land bridge formed by the Weddellian Isthmus. This bridge connected West Antarctica and southern South America, probably up to the early late Paleocene. The great importance of this material lies in the increase of the diversity in the mammalian fossil record in the Antarctic continent. Further studies and new materials could corroborate if MLP 12-I-20-4 is related to known South American lineages or represent a new group that could be part of an Antarctic endemism.