BIOGEOGRAPHIC CONNECTIONS OF THE EARLY PLIOCENE AGE GRAY FOSSIL SITE OF TENNESSEE WITH FAUNAS OF EURASIA AND MEXICO

The Gray Fossil Site (GFS) of northeastern Tennessee preserves incredibly diverse fauna and flora from the early Pliocene (4.9 to 4.5 Ma). As one of few late Neogene fossil sites in eastern North America and the only site of its age in the Appalachian region, GFS differs greatly from contemporaneous sites across the continent. While many vertebrate genera from GFS are known from other late Cenozoic fossil sites and persist within modern ecosystems, some taxa are common in Neogene and Quaternary faunas of Eurasia and Mexico but absent elsewhere in North America. These occurrences help document historical biogeographic connections between the eastern United States and those regions.

Dispersals between North America and Eurasia in the late Miocene and early Pliocene are well known, and some mammals from GFS add support to that major faunal dispersal event. The giant flying squirrel Miopetaurista ranges in Eurasia from China to Portugal, but early Pliocene records from GFS and Florida are the only ones in North America. Among GFS carnivorans are an ailurine (Pristinailurus), meline badger (Arctomeles), and wolverine (Gulo), lineages that are rare components of Neogene faunas in China and Russia. GFS eulipotyphlans include moles and shrews known from Neogene sites in Eurasia, including Parascalops, Mioscalops, Neurotrichus, a desman (Magnatalpa), Paenelimneocus, and Crusafontina. These taxa absent in the fossil record of western and central North America but present at GFS suggest dispersals likely occurred via an interchange route through the northern United States and Canada, evidence of which was subsequently wiped out by Pleistocene glaciation.

Other GFS taxa occur in Quaternary and modern faunas of North America, but are restricted to warmer, lower latitude sites. Among GFS reptiles reflecting that pattern are Alligator, beaded lizard (Heloderma), hooknose snake (Gyalopion), and tortoises (Testudinidae). Similarly, the leporid Notolagus is primarily known from lower latitude sites in the southwestern United States and Mexico. Two recently identified GFS cricetids, Neotomodon and Xenomys, are only known from the modern and late Pleistocene faunas of central Mexico. These occurrences suggest broader early Pliocene latitudinal distributions for these reptiles and small mammals, which likely became reduced due to late Pliocene and Pleistocene climate changes.