| Arsinoitherium | |
|---|---|
 | |
| A. zitteli cast,Natural History Museum, London | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | †Embrithopoda |
| Family: | †Arsinoitheriidae |
| Genus: | †Arsinoitherium Beadnell 1902 |
| Type species | |
| Arsinoitherium zitteli (Beadnell, 1902) | |
| Species | |
| |
Arsinoitherium is an extinct genus ofpaenungulatemammals belonging to the extinctorderEmbrithopoda. It is related toelephants,sirenians, andhyraxes. Arsinoitheres were superficiallyrhinoceros-likeherbivores that lived during the LateEocene and the EarlyOligocene ofNorth Africa from 36 to 30 million years ago, in areas oftropical rainforest and at the margin ofmangrove swamps. A species described in 2004,A. giganteum, lived inEthiopia about 27 million years ago.
The best-known (and first-described) species isA. zitteli. Another species,A. giganteum, was discovered in theEthiopian highlands ofChilga in 2003. The fossil teeth, far larger than those ofA. zitteli, date to around 28–27 million years ago.[1] While theFaiyum Oasis is the only site where complete skeletons ofArsinoitherium fossils were recovered, arsinoitheriids have been found in southeastern Europe, includingCrivadiatherium from Romania, andHypsamasia andPalaeoamasia from Turkey.
Thegeneric nameArsinoitherium comes fromPharaohArsinoe II (after whom theFaiyum Oasis, the region in which the first fossils were found, was called during thePtolemaic Kingdom),[2] and theAncient Greek word θηρίον (theríon), meaning "beast". Thespecies epithet of thetype species,A. zitteli, was given to it in honor of the eminent German paleontologistKarl Alfred Ritter von Zittel, regarded by some as the pioneer of paleontology in Egypt.[3]
Adults of the speciesA. zitteli stood around 1.75 m (5.7 ft) tall at the shoulders and 3 m (9.8 ft) in length.[4][5] It weighed 2.5 tons, only slightly smaller than the modernwhite rhino and due to the similar features and sizes,Arsinoitherium is commonly thought[by whom?] 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 backwards 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 ofArsinoitherium 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 modernbovids.[7][8] While reconstructions usually show them as similar to theossicones ofgiraffes, in life each bony core may have been covered, like the horn cores of bovids, with a large horn ofkeratin.[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]
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Fossils ofArsinoitherium have been found in:[12]
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