sexual dimorphism. These specimens are: HMV 0979, a complete young male skull, HMV 1098, a complete adult female skull and finally HMV 1099, known only from a mandible belonging to an adult that is missing the ascending ramus. All specimens were found from the lower part of the upper Miocene Liushu Formation in the Linxia Basin (Gansu, China). HMV 0979 and HMV 1099 were discovered at Houshan village, and HMV 1098 at Shanzhuang village. The studied skulls and mandible from the Linxia Basin, especially HMV 0979 and HMV 1099, are found to be generally similar to the skull and mandible of Iranotherium morgani from Maragha, with minor differences, like the length ratio of lower premolars to molars. This difference is considered to be due to individual or sexual variations and is not sufficient for establishing a new species. Hence, all three specimens described have been assigned to the genus Iranotherium by Deng. Based on the two skulls from the study, the Maragha specimen is identified as a male due to the presence of hemispherical rugosities on its zygoma. Paleobiology Feeding Iranotherium was a grazer since its denition is that of a hypsodont. In life it would've had wide and flat lips like those of the extant White Rhino. The absolute body size of an herbivore is very important in determining the fiber/protein ratio that an animal will be able to tolerate in its diet, as larger animals require proportionately less protein and will be able to tolerate a larger proportion of cellulose. Therefore, the giant body size of I. morgani implies that this species grazed high-fiber grasses. I. morgani obviously inhabited an open grassland. Sexual variation In 2005, two skulls of Iranotherium were described by Tao Deng. One skull was from an adult female Iranotherium and the other from a young adult male. These skulls, when compared showed significant, sexually dimorphic differences. The male had rugosities present on each zygomatic arch, whereas the females lacked them entirely. This unique feature is virtually unknown among other rhinocerotids. Male Iranotherium are hypothesized to bear it for supporting larger masseteric and temporalis musculature. Additional sexually dimorphic features include the zygomatic arch of the male being thicker than that of the female. The anterior part of the nasals are wider and rougher in the male, but narrow and smooth in the female; this difference is related to the huge horn boss in the male