Implications of the evolutionary stasis of Notiolofos arquinotiensis (Mammalia) Eocene of seymour island, Antarctica

GELFO J. N.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

International Palaeontological Association

The Sparnotheriodontidae litoptern Notiolofos arquinotiensis was the most abundant terrestrial placental mammal in the Paleogene of Antarctica. This herbivorous mammal was a low-crowned browser, with lophoselenodont and bicrescentic lower teeth and a strong lophoselenodont ectoloph and bunoid lingual cusp in the upper molars. Phylogeny and paleobiogeographic evidence indicates a South American origin of Sparnotheriodontidae, and an allopatric speciation event for the origin of N. arquinotiensis. It was recorded exclusively in Seymour Island, through most of the La Meseta Formation allomembers, including from base to top, Acantilados II, Campamento, Cucullaea I,and Submeseta. Isotopic and paleomagnetic calibration of the La Meseta Formation suggests an evolutionary stasis for Notiolofos of at least 17.5 Ma. The analysis of the morphological stability displayed by paleospecies requires a profuse fossil sample through the stratigraphic succession. Notiolofos remains comprise neither complete dental series nor abundant teeth; its hypodigm joins isolated teeth from different loci and from distinct stratigraphic levels. The stasis hypothesis is here tested as opposite to the possibility of a wider and non-previously identified specific diversity of the Antarctic parnotheriodontids. The materials available for Notiolofos were compared in their preservation, characters and dental occlusal areas to the more complete phylogenetic relative Sparnotheriodon epsilonoides and the North American Meniscotherium chamense. Despite there is not a direct phylogenetic relationship between Notiolofus and Meniscotherium, the morphological dental similitude between both suggests they could be interpreted as ecologically equivalent taxa. The analysis allows the reassignment of some Notiolofos teeth to other dental locus but not to consider a higher variation than previously described. The temporal scale of Notiolofos is appropriate to consider Court Jester hypothesis as the principal evolutionary force, so it could be expected that during this span, environmental change triggered speciation events. The present analysis indicates that there are no elements to justify the presence of different species through the stratigraphic sequence or to refute the morphological stasis in Notiolofos. In a reductionist perspective, this suggests a stability of the terrestrial physical conditions in West Antarctica during most of the Eocene, or at least, that any environmental change, particularly in climate and vegetation, was not enough to generate an evolutionary response.