Plionarctos (Ursidae; Tremarctinae) from the Gray Fossil Site and a reevaluation of the genus.

SCHUBERT, B.; WALLACE, S.; LEOPOLDO HECTOR SOIBELZON

UK

Congreso; SVP 69th Annual Meeting and the 57th Symposium of Vertebrate Palaeontology and Comparative Anatomy (SVPCA); 2009

The Gray Fossil Site (GFS) of northeastern Tennessee, USA is the only Mio-Pliocene fossillocality in the Appalachian Highlands and is producing a unique and diverse fauna froma forested environment. This ecological setting is well established based on plant fossils,isotopic analyses, and the recovered fauna. New species only known from the GFS includean ailurine panda (Pristinailurus bristoli) and Eurasian woodland badger(Arctomelesdimolodontus); both of which have forest affinities. In sum, the GFS is a sinkhole ponddeposit dated to late Hemphilian using mammalian biochronology: the extinction ofthe rhinoceros Teleoceras ~ 4.5 Ma and appearance of tremarctine bears ~ 7 Ma. Otherrecovered mammals are consistent with this age assignment. Bears are represented atGFS by mandibular and dental remains of the small tremarctine, Plionarctos. Two speciesare described in the literature, P. edensis and P. harroldorum; both from western NorthAmerica. Previous researchers considered these taxa to represent an anagenetic lineage,with the late Hemphilian – early Blancan P. edensis as the precursor of P. harroldorum(only recorded from the early Blancan). While Plionarctos specimens are known fromcentral and eastern North America, most are isolated teeth, and none are assigned to specieslevel. Specimens from the GFS include one dentary with teeth, one edentulous dentary, andisolated lower teeth. The described morphological features that separate P. edensis and P.harroldorum are primarily located on the M1 and M2. However, proportional differencesin size and shape of m1 and m2 are also noted in the diagnoses. Based on these dimensionsthe GFS Plionarctos diverges more from both P. edensis and P. harroldorum than theydo to each other. Whether or not this indicates a third species of Plionarctos or regionalvariation is not yet clear. Because living ursid species exhibit morphological plasticity indental dimensions we proceed cautiously with the specific diagnosis of the GFS Plionarctosspecimens.