EVIDENCE OF A FOREST REFUGIUM AT A NEOGENE FOSSIL SITE, GRAY, TN

The Gray Fossil Site in eastern Tennessee, which is biostratigraphically dated between 4.5 and 7 Ma, can clarify paleoecological dynamics during the Neogene. In particular, the potential of identifying a forest refugium will better our understanding of the environmental context of mammalian evolution during the late Cenozoic. Stable isotope analyses of bulk and serial samples of fossil tooth enamel from all herbivorous mammals present at the Gray site elucidate paleoecological reconstructions. The herbivorous mega fauna include taxa of likely Eurasian ancestry including: the tapir Tapirus polkensis, rhino Teleoceras cf. T. hicksi , camel cf. Megatylopus sp., peccary Tayassuidae, and proboscidean Gomphotheriidae. The tapir, rhino, camel, and peccary all yield stable carbon isotope data with average values of -12.2‰, -13.2‰, -13.8‰, and -13.1‰, respectively, suggesting forest-dwelling browsers. This range of δ¹³C_enamel values indicates the presence of a C₃ dominated floral environment. Because δ¹³C values decline with increasing canopy density, the ancient temperate forests from the Gray site were relatively dense. The lack of significant C₄ floral consumption (i.e., tooth enamel δ¹³C values < -9‰) suggests the presence of forests large enough to independently support the continued browsing of sustainable populations of browsers from the Gray site. In contrast, bulk and serial δ ¹³C values ranging from -0.7‰ to 0.3‰ from a gomphothere tusk support a diet consisting of dominant C₄ flora. The analysis of trace elements and/or strontium isotopes of the gomphothere tusk may assist in determining if an alternate origin is responsible for the isotopic differences. Carbon and oxygen serial sample variation of the tapir, rhino, peccary, and proboscidean is less than 1.5‰, suggesting little difference in seasonal temperature and/or precipitation. These data support the presence of North American forest refugia in the southern Appalachians during the Neogene.