Systematic and paleoecological study of the new remains of Brachypotherium (Rhinocerotidae) from the Middle Miocene Siwaliks (Pakistan)

Abstract

Newly discovered rhinocerotid remains from the Middle Miocene (14.2–11.2 Ma) of the Siwaliks of Pakistan are described in this paper, adding new data to the existing rhinocerotid fossil record from the Siwalik region. The specimens are identified as belonging to a teleoceratine genus Brachypotherium on the basis of morphometric comparison with the previously known rhinocerotid specimens from the Siwaliks as well as other biogeographic regions. The article provides additional information on the systematics through the dental morphological comparison of the genus Brachypotherium and in particular of Brachypotherium perimense and Brachypotherium fatehjangense. The data indicate an increased teeth size and dental morphological variations in B. perimense by changing environment from the Middle to Late Miocene and morphological differences in B. fatehjangense from B. brachypus. Also, an attempt has been made to clarify the dental morphological differences among different Middle Miocene rhinocerotid species of the Siwaliks. The hypsodonty and thick enamel of the studied samples indicates the presence of grazing communities feeding on coarse grasses during the Middle Miocene of the Siwaliks. The ecological implications of the genus Brachypotherium toward the changing Middle Miocene climatic conditions on the basis of stable isotope and enamel hypoplasia analyses are also discussed. The results of these proxies indicate that the Brachypotherium perimense preferred woodland and ponds, while B. fatehjangense lived in a more forested environment with river system. The transitional pattern of the Middle Miocene Siwaliks of Pakistan from dry to more precipitation and humidity might had some more ecological pressure on B. fatehjangense than on B. perimense.