Neogene forests from the Appalachians of Tennessee, USA: Geochemical evidence from fossil mammal teeth

Neogene land-mammal localities are very rare in the northeastern U.S.; therefore, the late Miocene/early Pliocene Gray Fossil Site in eastern Tennessee can clarify paleoecological dynamics during a time of dramatic global change. In particular, the identification of ancient forests and past climate regimes 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 ungulates present at the Gray site elucidate paleoecological reconstructions. The herbivorous megafauna include taxa of likely North American and 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 yield mean stable carbon isotope (delta C-13) tooth enamel values of -13.0 parts per thousand, -13.3 parts per thousand, -13.8 parts per thousand, and -13.1 parts per thousand, respectively, suggesting forest-dwelling browsers. This range of delta C-13 values indicates the presence Of a C-3 dominated ancient local flora. Because delta C-13 values decline with increasing canopy density, the ancient temperate forests from the Gray site were moderately dense. The lack of significant C-4 plant consumption (i.e., tooth enamel delta C-13 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 delta C-13 values ranging from -0.7 parts per thousand to 0.3 parts per thousand from a gomphothere tusk support a diet consisting of C-4 grasses, suggesting the presence of C-4 grasslands within the individuals home range. The rare earth element (REE) analyses of the gomphothere tusk and the teeth of Tapirus and Teleoceras indicates that these individuals shared similar depositional environments; thus, demonstrating the concurrent presence of C-3 forests and C-4 grasslands in the northeast. Stable carbon and oxygen serial sample variation of the tapir, rhino, peccary, and gomphothere is less than 1.5 parts per thousand, suggesting minor differences in seasonal temperature and/or precipitation. These data support the possibility of a North American forest refugium in the southern Appalachians during a time typified by more open environments. (c) 2008 Elsevier B.V. All rights reserved.