Deciduous dentition and ontogenetic development of the skull and teeth of Chilotherium (Mammalia, Perissodactyla, Rhinocerotidae) from the Late Miocene of Eurasia

The hornless rhinoceros genus Chilotherium is characterised by high taxonomic complexity, with more than 30 species having been included in the genus at some point. This frequently prevents the identification of incomplete material, which has historically limited understanding of the genus’s diversity and evolution. Although recent work has enhanced the comprehension of the systematics of hornless rhinoceroses, the ontogeny of the cranium and deciduous dentition of chilotheres is still poorly known.

Herein, juvenile skulls and mandibles at different ontogenetic stages are investigated, along with the deciduous teeth of four Late Miocene chilothere species: Chilotherium persiae from Maragheh (Iran), Chilotherium habereri from Kutschwan (China), Chilotherium schlosseri from Samos (Greece), and Chilotherium anderssoni from Daijiagou (China). The results show that several dental characters in the deciduous premolars are informative for species discrimination.

The eruption sequence of the deciduous teeth is broadly uniform within the genus. Only the relative eruption of D 1 and D 4 varies, with C. schlosseri showing delayed D 1 eruption. Lastly, enamel hypoplasia is also documented in the deciduous teeth.

Although d / D 2 and d / D 3 exhibit hypoplasias only sporadically, d / D 4 consistently bears prominent hypoplasias associated with the individual’s birth. The position of the latter hypoplasia is consistent across chilotheres, occurring in the middle of the tooth crown, except in C. schlosseri, where it is located at the base of the crown.