Revision of the Late Miocene hornless rhinocerotids from Samos Island (Greece) with the designation of neotypes and implications for the European chilotheres

Extant rhinoceroses are represented only by five species and are characterized by the presence of a nasal horn. In the past, they were much more diverse, with one of the best-known groups being the aceratheriines, i.e., hornless rhinoceroses. Chilotheres are a group of hornless rhinos that inhabited Eurasia during the Late Miocene. Their westernmost geographic range reached Eastern Europe, where overall eight species have been erected. Four of these were described based on material from the Upper Miocene of Samos Island (Greece), two of which are not considered valid anymore. Unfortunately, the type skulls of all four species are lost and there are several issues concerning their taxonomy. Therefore, we herein designate two skulls housed in historical collections from Samos as neotypes for the first two species, Chilotherium schlosseri (Weber, 1905) and Eochilotherium samium (Weber, 1905), and provide detailed comparisons for the separation of the species from each other and from any other chilotheres. Our results prove that the two species are valid and justify their separation on a generic level. Chilotherium schlosseri seems to be more closely affiliated with the other European Chilotherium species, whereas E. samium is more similar to the Chinese 'Chilotherium' wimani and 'Chilotherium' primigenium, based on their more plesiomorphic characters.