and the smaller horn boss in the female. Because the nasal horn boss of the male is a large dome, its nasal groove is distinctly deeper than that of the female. The nasal horn boss of the male is much rougher and likely to have supported a larger horn than that of the female. The skull roof of the male is less curved than that of the female, and the frontal region of the male is more convex than that of the female. Therefore, the overall structure of the whole skull of the male is more robust than that of the female. These features, especially the huge nasal horn, could be used for defense or competition for mates. The zygomatic rugosities of the male I. morgani could have supported a horn-like callused structure for combat or for display. Because these hypertrophies are different from the horn boss rugosities associated with the true horns in rhinos, they are probably indicative of the presence of larger masseteric and temporal muscles and the overall robustness of the skull. Distribution and Paleoecology Iranotherium is so far only known from Iran and China. It lived in a forested environment in Iran whereas it occupied a more open habitat in China. In Iran, Iranotherium is known from the middle local biozones of the Maragha fauna, from an age of between 9 and 7.6 Ma. Over there, it coexisted with Hipparion prostylum, Mesopithecus pentelici and Indarctos maraghanus In China, Iranotherium is known from the middle part of the Liushu formation of the Linxia Basin. I. morgani appeared in Linxia earlier than in Maragha. I. morgani is likely to have first appeared in northwestern China and then dispersed westward to central Asia. The fauna that Iranotherium was a part of is known as the Dashengou fauna. It was contemporary with one glire (Pararhizomys hipparionum), four mustelids (Promephitis sp., P. hootoni, Melodon majori, Sinictis sp.), four hyaenids (Ictitherium sp., Hyaenictitherium wongii, H. hyaenoides, Dinocrocuta gigantea), two cats (Amphimachairodus giganteus, Felis sp.), one proboscidean (Tetralophodon exoletus), four perissodactyls (Hipparion chiai, H. weihoensis, Acerorhinus hezhengensis, Chilotherium wimani), seven artiodactyls (Chleuastochoerus stehlini, Dicrocerus sp., Samotherium sp., Honanotherium schlosseri, Gazella sp., Hezhengia bohlini, and Miotragocerus sp.) Based on pollen analysis, the vegetation of the Liushu Formation belonged to an arid steppe. References Bibliography Deng, T. (2005). New discovery of Iranotherium morgani (Perissodactyla, Rhinocerotidae) from the late Miocene of the Linxia Basin in Gansu,