Arsinoitherium

Arsinoitherium (Arsinoe II's beast) is an extinct genus of paenungulate mammals belonging to the extinct order Embrithopoda. It is related to elephants, sirenians, and hyraxes. Arsinoitheres were superficially rhinoceros-like herbivores that lived during the Late Eocene and the Early Oligocene of North Africa from 36 to 30 million years ago, in areas of tropical rainforest and at the margin of mangrove swamps. A species described in 2004, A. giganteum, lived in Ethiopia about 27 million years ago.

Adults of the species A. zitteli stood around 1.75 m (5.7 ft) tall at the shoulders and 3 m (9.8 ft) in length. A. zitelli has been estimated to have weighed anywhere from 510–1,500 kg (1,120–3,310 lb), whereas A. giganteum estimates range from 1,760–1,960 kg (3,880–4,320 lb). The most noticeable features of Arsinoitherium were a pair of enormous horns above the nose and a second pair of tiny knob-like horns over the eyes. These were structurally similar to the horns of modern bovids. While reconstructions usually show them as similar to the ossicones of giraffes, in life each bony core may have been covered, like the horn cores of bovids, with a large horn of keratin. Both males and females had horns. While some investigators have described a larger and a smaller species from the same site, others have identified the difference in body and tooth size as sexual dimorphism.

Arsinoitherium superficially resembles a species of rhinoceros, but it is not closely related as it is not a perissodactyl; instead, their closest extant relatives are elephants and manatees. Fossils have been found in sediments deposited in coastal swamps and warm, humid, heavily vegetated lowland forests across what is now Africa and Arabia.