MAMMALIAN HERBIVORE COMMUNITIES, ANCIENT FEEDING ECOLOGY, AND CARBON ISOTOPES - A 10-MILLION-YEAR SEQUENCE FROM THE NEOGENE OF FLORIDA

Medium- to large-bodied mammalian herbivores are taxonomically diverse and comprise a large component of the highly fossiliferous Neogene te rrestrial sedimentary sequence from Florida. In order to reconstruct h erbivore paleodiets and community paleoecology as well as understand c limate and ecosystem change, 112 pristine tooth enamel samples were an alyzed for at least 12 families and 26 genera within the orders Probos cidea, Perissodactyla, and Artiodactyla. These samples are from 17 loc alities and seven time horizons of late Miocene (Hemphillian) through late Pleistocene (Rancholabrean) age and between about 9.5 Ma to 100,0 00 yrs ago. Stable carbon isotopic analyses indicate that during the l ate Miocene local terrestrial communities and herbivore paleodiets con sisted exclusively, or predominantly, of C3 plants, e.,a., mean tooth enamel delta(13)C value is -11.9 parts per thousand from the 9.5 Ma le vel. During the latest Miocene-early Pliocene (after 7 Ma) there is a shift in mean delta(13)C values of tooth enamel to -7.0 parts per thou sand (4.5 Ma level). This shift appears to correspond to other late Mi ocene delta(13)C shifts reported elsewhere in terrestrial and oceanic sedimentary sequences. On land, this shift is interpreted to represent the spread of isotopically more positive C4 grasses and probable chan ge in diet from predominantly C3 to mixed C3/C4 plant foodstuffs. In g eneral, the delta(13)C data reported here indicate that within the Flo rida sequence: (1) some families have remained predominantly browsers (Mammutidae, Tapiridae, Camelidae, Palaeomerycidae, and Cervidae); (2) some are predominantly C4 grazers (Elephantidae, Bovidae); (3) others consisted of mixed C3/C4 diets (Amebelodontidae, Gomphotheriidae, Equ idae, Rhinocerotidae); and, based also on modem diets, (4) the isotopi cally intermediate peccaries (Tayassuidae) may have fed on CAM succule nts. While these results generally confirm previous paleodietary hypot heses based on relative crown height, there also are some notable surp rises in light of the stable carbon isotopic analyses.