Iranotherium ("Beast of Iran") was a genus of large elasmotheriine rhinoceros, comparable in size to a modern white rhino. It is known from the Late Miocene (Tortonian) of Maragha, Iran and the middle part of the Liushu formation of northwestern China. It was a precursor to the related Sinotherium and may have been ultimately outcompeted by its descendant. This species is most well known for showing unique sexual dimorphism among rhinos. Description Iranotherium is only known from cranial material, and rare postcranial elements. Skull and Horn The skull is long and dorsally concave, with a length of 775 mm. The parietal crests are broad, the nasal bone is long and wide, with a shallow U-shaped nasal notch, the orbit is prominent and has a high position close to the skull roof, the first half of the zygomatic arch is narrow. The skulls also show distinct sexual dimorphism: The base from which the horn grows is large and strong in the male, while it is small and weak in the female, and there is strong and rough rugosities present on the back half part of the zygomatic arch of the male. The back half of the zygoma is also uplifted and higher than the skull roof. Dentition Iranotherium teeth are hypsodont, (they were covered and filled by cement), meaning that Iranotherium was a grazer that fed on grasses. Its upper incisors are completely absent and the premolars are significantly shortened, however, the cheek teeth are longer in the male than in the female. Discovery and History Original Discovery When Iranotherium was originally discovered from teeth, it was recognized that this species was similar to the rhino Elasmotherium and was the ancestor of the latter (This was before Sinotherium was discovered), however in 1908, when it was published as a new species, it was strangely referred to the genus Rhinoceros. In 1924, the material of R. morgani from Maragha was further described. Ringström suggested that this species did not belong in Rhinoceros, referring it to his new genus Iranotherium as I. morgani. Iranotherium as a genus was originally described in 1908 by Mecquenem where no holotype was designated for the genus. Specimen MNHN 1905–10, and atlas from Maragha, Iran was chosen as the Lectotype for this genus. Later Discoveries In 2005, three specimens of Iranotherium were described by Tao Deng. Two of these specimens were complete skulls that showed evidence of unique