Tale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida Neogene

Carbon (δ 13 C) and oxygen (δ 18 O) isotopic results are presented from 42 tooth enamel carbonate samples of rhinos (Family Rhinocerotidae) from a sequence of Florida Neogene localities between 9.5 and 4.5 Ma. These data are used to interpret ancient diets and test previous hypotheses of terrestrial/aquatic adaptations of two sympatric rhinos, Aphelops and Teleoceras . The long-limbed, shorter-crowned Aphelops traditionally has been reconstructed as an open-country browser (similar to the modern black rhino), whereas short-limbed, higher-crowned Teleoceras traditionally has been reconstructed as an amphibious grazer (similar to the modern hippo). Between about 9. 5 and 7 Ma the δ 13 C values (all <−11.0‰) from Florida Aphelops and Teleoceras indicate that both rhinos were feeding on C 3 plants. This diet probably included a combination of browse and C 3 grasses, although the exact proportions for each genus cannot be distinguished isotopically. In contrast, after the late Miocene global carbon shift as represented at 4.5 Ma in Florida, Aphelops was a browser (mean δ 13 C = −11.9‰), whereas Teleoceras was a mixed feeder/C 4 grazer (mean δ 13 C = −7.0‰). Oxygen isotopic values indicate that neither Aphelops nor Teleoceras was principally aquatic. Given these new isotopic data, more plausible modern analogs for these two extinct rhinos are, respectively, the terrestrial browsing black rhino ( Diceros bicornis ) and the terrestrial grazing white rhino ( Ceratotherium simum ), which are sympatric today in Africa.