PALEOBIOGEOGRAPHY OF THE GENUS CHILOTHERIUM (MAMMALIA, PERISSODACTYLA, RHINOCEROTIDAE) IMPLIES EXPLOITATION OF ECOLOGICAL NICHES NOT UTILIZED BY EXTANT RHINOS

Modern rhinos (Mammalia, Perissodactyla, Rhinocerotidae) are found in South East Asia and across Africa and occupy a narrow range of ecological niches. All modern species are found in low-elevation habitats at warm temperatures, ranging from tropical rainforests to savannahs. As the fossil distribution and diversity of this family is much higher, we set out to test if some fossil rhinos, specifically the genus Chilotherium, occupied an ecological niche novel to those seen today. We looked at geographic and temporal distributions of the genus as compared to paleoelevation and paleoclimatic data. While the genus was likely a generalist herbivore capable of exploiting a broad ranch of ecological niches, several habitats not utilized by modern members of the family emerged from our literature searches. We propose Chilotherium was able to exploit higher elevation ecosystems, such as steppe grasslands and shrubby alpine meadows, than any modern elevation or temperature range seen in extant Rhinocerotidae. We selected the genus Chilotherium to test this hypothesis on because of a broad geographic and temporal range coupled with well-studied paleoecological reconstructions and plentiful published occurrences. Containing several recognized species, the genus spans the Miocene into Pliocene epochs, ranging from the Mediterranean to South East Asia. We further noted geographic and paleoelevation limits to species or species groups, forming a Mediterranean, Tibetan Plateau, and Northern China biogeographic distributions with an additional temporal gradient. Taxonomy and distribution data was taken from the New and Old Worlds Database (NOW) and the Paleobiology Database (PBDB), cross referenced with several paleoelevation and paleoclimatic models spanning the Miocene to Pliocene.