Chilotherium

Species

Twelve species of Chilotherium have been described and 19 other species have been assigned the genus. Nine are considered valid: four from Europe, one from Iran, and four from China.^[3]

Aprotodon differs from Chilotherium in its proportionally larger and wider symphysis; the horizontal mandibular ramus is curved both in side view and in dorsal view, unlike most rhinocerotids; and the premolars are semi-molariform, unlike the fully molariform premolars in Chilotherium. In Subchilotherium the mandibular symphysis is much more narrow than in Chilotherium. Acerorhinus has a strongly constricted nasal base and a mandibular symphysis that is narrow compared to that in Chilotherium.^[3]

Social behavior

Much like modern rhinoceros, C. wimani had a polygynous mating system. The tusk of males were usually broken or more worn down the tusks of females, which suggests increased agnostic interactions among males during sexual combat. Young males likely had a higher mortality than females due to competition with adults and predators. The abundance of C. wimani in Linxia Basin would suggest this species were likely traveled in herds.^[6]

Diet

Chilotherium were a group of grazing animals that radiated into several subgenera and species. Their feet were tridactyl and their legs shorter than in related groups.^[8] A few of them remained browsers, such as C. persiae,^[9] but most of them were adapted to a grass-based diet, hence the short legs. Their heads were horn-less but equipped with tusk-like lower incisors and were held in a horizontal position, in contrast to modern rhinos. They inhabited the so-called sub-Paratethyan or Greek-Iranian province during the late Miocene when this region was invaded by advanced rhinos from Africa, such as Ceratotherium (modern white rhinos). Like them, Chilotherium gradually evolved into specialised grazers, including hypsodont teeth and shortened metapodials.^[8] Dental microwear recovered C. schlosseri as a grazer.^[10]

On the other hand, isotopic analysis found C. intermedium was a browser and likely lived in forested environments, alongside Deinotherium. Both herbivores niche partitioned as Chilotherium preferred habitats very close to bodies of water compared to Deinotherium.^[11]

Palaeopathology

A female Chilotherium skull bears the distinctive bite marks of Dinocrocuta gigantea on the forehead. Based on the regrowth of bone around the injury, the rhinoceros escaped the predator's attack and later recovered.^[12]