The best-known (and first-described) species is A. zitteli. Another species, A. giganteum, was discovered in the Ethiopian highlands of Chilga in 2003. The fossil teeth, far larger than those of A. zitteli, date to around 28–27 million years ago.[1] While the Fayum Oasis is the only site where complete skeletons of Arsinoitherium fossils were recovered, arsinoitheriids have been found in southeastern Europe, including Crivadiatherium from Romania, and Hypsamasia and Palaeoamasia from Turkey.
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.[4][5] It measured 2.5 tons, only slightly smaller than the modern white rhino and due to the similar features and sizes, Arsinoitherium is commonly thought to be an extinct rhinoceros species, but it is not closely related to rhinos; instead, their closest extant relatives are elephants and manatees. They were massive, slow-moving animals with forelimbs adapted for pulling strongly backward rather than swinging forward, a feature typical of animals that punt themselves through shallow water or walk on soft, sticky ground. Fossils are found in sediments deposited in coastal swamps and warm, humid, heavily vegetated lowland forests across what is now Africa and Arabia.[6] 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.[7][8] While reconstructions usually show them as similar to the ossiconesofgiraffes, in life each bony core may have been covered, like the horn cores of bovids, with a large horn of keratin.[9] 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.[10] The skeleton is robust and the limbs were columnar, similar to those of elephants; the hips were also elephant-like,[4] and arsinotheres were not built to run. Arsinoitherium had a full complement of 44 teeth, which is the primitive state of placental mammalian dentition. However, the genus had a unique and highly specialized way of chewing, shifting the jaw joint to produce constant pressure along its continuous row of teeth; it has been reconstructed as a highly selective browser.[11]
^Sanders, W.J., Kappelman, J., and Rasmussen, D.T. 2004. New large−bodied mammals from the late Oligocene site of Chilga, Ethiopia. Acta Palaeontologica Polonica 49 (3): 365–392.[1].
^Andrews, C. W. (1906). A descriptive catalogue of the Tertiary Vertebrata of the Fayum. Publ. Brit. Mus. Nat. Hist. Land. XXXVII.
^Anonymous. (1903). A New Egyptian Mammal (Arsinoitherium) from the Fayûm. (1903). Geological Magazine, 10(12), 529-532.
^Turner, Anton, Alan, Mauricio (2007). Evolving Eden: An Illustrated Guide to the Evolution of the African Large-Mammal Fauna. Columbia University Press. ISBN978-0231119450.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Sanders, W. J., Kappelman, J., & Rasmussen, D. T. (2004). "New large-bodied mammals from the late Oligocene site of Chilga, Ethiopia". Acta Palaeontologica Polonica. 49 (3).{{cite journal}}: CS1 maint: multiple names: authors list (link)
