GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 162-19
Presentation Time: 9:00 AM-6:30 PM


WANG, Bian, Earth and Environmental Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Avenue, Ann Arbor, MI 48109 and SECORD, Ross, Department of Earth & Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0340,

Members of the family Rhinocerotidae were one of most successful mammal groups of the Oligocene and Miocene in North America. Their extinction in the early Pliocene has been attributed to several causes associated with environmental change. This study uses stable isotopes to test whether or not the last North American rhinoceroses, Aphelops and Teleoceras, were able to adapt to the expansion of C4 grasslands in the Great Plains during the Hemphillian land-mammal age.

Stable carbon isotopes were sampled from the tooth enamel carbonate of 38 Teleoceras and 22 Aphelops specimens, spanning the Hemphillian and Hh2 to Hh4 biochrons, respectively. Mean δ13CE values of Teleoceras in Hh1 through Hh4 are -8.4±0.5‰ (1 S.D.), -9.1±1.0‰, -8.8±1.2‰, and -10.0±1.0‰, respectively. Mean δ13CE values of Aphelops in Hh2 through Hh4 are -8.7±1.5‰, -10.1±2.2‰, and -10.7±0.7‰, respectively, exhibiting a wider range of values than in Teleoceras. The majority of samples for both genera plot in dry, water-stressed C3 habitats, with the possibility of a small C4 component, while a smaller number of individuals plot in the wetter, open canopy C3 range. A few individuals show unequivocal C4 signals (>-7.7‰). Aphelops and Teleoceras δ13CE values exhibit no significant temporal changes (Aphelops, p>0.15; Teleoceras, p>0.05; Mann-Whitney) and cannot be statistically distinguished from each other in any biochron or any single locality in which they co-occur (p>0.09, Mann-Whitney).

Results indicate that both rhinos remained primarily C3 feeders during C4 expansion, with the ability to incorporate only a small amount of C4 in their diet. In contrast, horses show greater C4 consumption at this time. The high δ13CE values in most Aphelops and Teleoceras, with many plotting in the water-stressed C3 range, suggest that these rhinos occupied primarily dry, open habitats, such as grasslands.

Rhinoceros δ18OE values generated for this study decrease latitudinally (δ18OE [‰] = -1.04 [±0.07] * Latitude [°] + 67.02[±8.11], r2 = 0.74, p<0.001), indicating a strong latitudinal δ18O gradient comparable to those recorded in other stable isotope proxies, probably reflecting a temperature gradient. This suggests that these large herbivores effectively tracked δ18O values in meteoric water and are potentially useful for paleoclimate reconstructions.