A New Phylogenetic Analysis of Tremarctine Bears

SOIBELZON, L.H.; SCHUBERT B.W.; POSADAS, P.E.

Río de Janeiro

Simposio; VII Simposio Brasileiro de Paleontología de Vertebrados; 2010

The subfamily Tremarctinae is distributed exclusively in America from the Late Miocene to present times. It comprises four genera: Plionarctos, Arctodus, Arctotherium, and Tremarctos. Plionarctos is known from the Late Miocene and Pliocene of North America and is considered to be ancestral to all other members of the subfamily.  Arctodus includes two North American species: A. pristinus and A. simus. Arctodus pristinus occurs in the Late Pliocene and Early to Middle Pleistocene, while A. simus is restricted to Middle and Late Pleistocene.  Arctotherium has five South American Pleistocene species. Arctotherium angustidens is recorded exclusively in the Late Pliocene to Middle Pleistocene of Bolivia and Argentina. The remaining four species come from the Middle Pleistocene to Early Holocene: Arctotherium vetustum and A. bonariense from Argentina; A. wingei from Bolivia, Venezuela and Brazil, and A. tarijense from Bolivia, Argentina and southern Chile. Finally, Tremarctos has one extinct species - T. floridanus - from the Late Pliocene and Pleistocene of North America, and a living one from South America, T. ornatus, which has not been recorded as a fossil. The Tremarctinae are a monophyletic group, with Plionarctos and Tremarctos as the basal genera, and the short-faced bears clade, formed by Arctodus and Arctotherium as the sister group. This hypothesis is congruent with the fossil record. Within the Arctotherium species, A. vetustum and A. wingei are morphologically more primitive than A. angustidens. Finally, A. bonariense and A. tarijense are the most derived species. Although this analysis agrees with previously reported relationships of the clades, it shows that much more work is needed to understand the phylogenetic relationships of South and North American carnivorans. Parsimony analysis was applied to analyze the distribution of the phylogenetic relationships of all Tremarctinae (Carnivora, Ursidae) taxa. The analysis was carried out using the computer programs NONA and Piwee, based on a data matrix built with 11 Tremarctinae taxa as ingroup and Ursus americanus as outgroup, and 41 characters. Applying the exact algorithm branch and bound, 2 trees were obtained with 26 steps, a consistency index of 0.73, and a retention index of 0.50.