Mammalian herbivore communities, ancient feeding ecology, and carbon isotopes: A 10 million-year sequence from the Neogene of Florida

Abstract

Medium- to large-bodied mammalian herbivores are taxonomically diverse and comprise a large component of the highly fossiliferous Neogene terrestrial sedimentary sequence from Florida. In order to reconstruct herbivore paleodiets and community paleoecology as well as understand climate and ecosystem change, 112 pristine tooth enamel samples were analyzed for at least 12 families and 26 genera within the orders Proboscidea, Perissodactyla, and Artiodactyla. These samples are from 17 localities and seven time horizons of late Miocene (Hemphillian) through late Pleistocene (Rancholabrean) age and between about 9.5 Ma to 100,000 yrs ago. Stable carbon isotopic analyses indicate that during the late Miocene local terrestrial communities and herbivore paleodiets consisted exclusively, or predominantly, of C3 plants, e.g., mean tooth enamel δ¹³C value is −11.9%_o from the 9.5 Ma level. During the latest Miocene-early Pliocene (after 7 Ma) there is a shift in mean δ¹³C values of tooth enamel to −7.0%_o (4.5 Ma level). This shift appears to correspond to other late Miocene δ¹³C 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 change in diet from predominantly C3 to mixed C3/C4 plant foodstuffs. In general, the δ¹³C data reported here indicate that within the Florida 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, Equidae, Rhinocerotidae); and, based also on modern diets, (4) the isotopically intermediate peccaries (Tayassuidae) may have fed on CAM succulents. While these results generally confirm previous paleodietary hypotheses based on relative crown height, there also are some notable surprises in light of the stable carbon isotopic analyses.