THE ?SOUTH AMERICAN? SHORT-FACED BEAR ARCTOTHERIUM FROM THE YUCATÁN PENINSULA OF BELIZE AND MEXICO: IMPLICATIONS FOR THEIR BIOGEOGRAPHY, PALEOBIOLOGY, EVOLUTION, AND EXTINCTION

SCHUBERT B.W.; CHATTERS, JC; ARROYO CABRALES, J; SOIBELZON, L.H.; GRIFFITH, CS; DE ANDA, G; LUNA HERRERA, P

Congreso; 2016 Annual Meeting of SVP; 2016

Short-faced bears (Subfamily Tremarctinae) are a group of American ursids that are mostly extinct. Theearliest member of the group, Plionarctos, appears in the latest Miocene of North America and disappearsby the middle Pliocene. Tremarctos emerges in the Pliocene and is best represented in the southeasternUnited States from the Pleistocene. Tremarctos ornatus is the only extant tremarctine, and is currentlyrestricted to South America. The fossil record of T. ornatus is sparse, and isn?t known until the Holocene.Arctodus first occurs in the late Pliocene of North America and by the middle Pleistocene was representedby A. simus, an exceedingly large bear that occurred across the continent. The genus Arctotheriumappears in South America in the early Pleistocene, and in contrast to the evolutionary trajectory ofArctodus, the earliest Arctotherium species (A. angustidens) was the largest, and the terminal Pleistocenespecies (A. wingei) was diminutive. Here we add to the understanding of tremarctines by describing thefirst records of Arctotherium outside South America. These specimens are from the Yucatán Peninsula,and are recorded from three cave sites. This includes a partial right maxilla with M1 and M2 from ActunHalal, Cayo District, Belize, and two underwater sites from Mexico that have multiple individualskeletons preserved. One of these caves, Hoyo Negro from Quintana Roo, has at least six skeletons andsome material has been collected. This includes complete crania from an adult and subadult, as well asdentaries and cervical vertebrae from the subadult. The adult skull has been radiocarbon dated as latestPleistocene, and is similar in age to other large mammals from the site, including an early human (Homosapiens) partial skeleton (known as ?Naia?). The bear material analyzed from Hoyo Negro represents themost complete examples of Arctotherium skulls from the late Pleistocene, and together with the materialstill in the underwater caves, represents the most complete fossil skeletons known for the entiresubfamily, from Miocene through Pleistocene. The occurrence of Arctotherium in the Yucatán indicates arange extension for the genus of at least 1500 km outside South America, and demonstrates our limitedknowledge of late Pleistocene communities of this region. The relative absence of Tremarctos and otherbears in South America during the Pleistocene may be a reflection of Arctotherium filling the bear nichethroughout Central America until their extinction in the latest Pleistocene or early Holocene.