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Species and Distribution

Arsinoitherium lived in Africa and the Arabian Peninsula from the Late Eocene into the Middle Oligocene (45 – 24 myo). There are 3 species: A. zitteli, A. giganteus, and N. blackcrowense.

A. zitteli, the original species, is only found in the Jebel Qatrani Formation in Fayum, Egypt. This is also the only location where nearly complete specimens have been recovered (Site F on map below).
An additional species, A. andrewsi, is probably synonymous with A. zitteli. Fossils of A. andrewsi are most likely large A. zitteli specimens (Werdelin and Sanders, 2010).

A. giganteus is a newer large species discovered in 2004 in the Chilga region of Ethiopia (Site C on map below) (Sanders et al, 2004). Tooth size comparisons indicate it was approximately 25% larger than A. zitteli, which would be slightly larger than a large White Rhino.

Another Arsinoitheriid is Namatherium blackcrowense from the Middle Eocene of Namibia. This animal is smaller than the other Arsinoitheriums and is the earliest occurence of these animals.

There have also been fragments (mainly teeth) of the genus (uncertain species) found in various African and Middle Eastern countries, including the Late Eocene of Libya and Tunisia, and the Early Oligocene of Angola, Oman, Saudi Arabia, and Kenya. These additional sites (minus the Middle East sites) can be seen on the map below. The Eragaleitt beds (27.5 - 24 myo) in Kenya are the last occurrence of Arsinoitherium.

There are also closely related animals that belong to the same Arsinoitheriidae family, such as Crivadiatherium and Palaeoamasia, that are found in Romania, Turkey, the Middle East, Asia, and Africa.

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Description and Paleoecology

Description

At approximately 6 feet tall and 11 feet long, Arsinoitherium zitteli is similar in size and shape to the White Rhinoceros. With its giant twin horns, it looks like a fanciful version of a rhino, however, it is not closely related to rhinos at all. Instead, it’s a genus of paenungulate mammals, which include Elephants, Sirena (dugongs and manatees), hyraxes, and the extinct Desmostylians.

Arsinoitherium’s bone structure is very different than a rhino’s. Examples include its columnar legs, which are distinctly elephant-like, plus its elephant-like hips, feet, and skull features.

The horns are also very different from a rhinoceros. These twin horns could grow to over 2.5 feet in length. The animal also had a much smaller pair of horns above the eyes. Rhino horns are completely made of keratin, where Arsinoitherium horns are hollow and made of bone. Witton briefly looked at the structure of the horns and compared them to modern animals. They most closely resemble bovid (cow) horns and probably had a keratin sheath over them like a cow (Witton 2017). Witton also says the keratin would have strengthened the horns, as the hollow horns would have been fragile and prone to fracturing.

Paleoecology

Formations that Arsinoitherium have been found indicate tropical forests and edges of mangrove swamps.

A common misconception is that Arsinoitherium spent much of its time in water, like a hippopotamus, feeding on aquatic vegetation. This misconception arises because Arsenoitherium was poorly designed for running. However, research has shown it was fully terrestrial. Other fossils found with Arsinoitherium support a fully terrestrial environment. Also, a stable isotope analysis was done on the Arsinoitherium fossil which indicates it was a terrestrial feeder (Clementz et al., 2008). It may have been poorly designed for running because it didn’t need to run, as it was one of the largest mammals in Africa in its time!

Arsenoitherium also has a specialized tooth design and specific attachment points for muscles in its jaws which indicate a very specialized diet. Court, 1992b suggested it may have eaten bulky fruits. This type of food is also abundant at the Fayum site in Egypt where A. zitteli is found.

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Extinction - The Expansion of Grasses

Like most mammals, including Deinotherium and the Brontotheres, climate change and the resulting disruption of habitat is responsible for Arsinoitheriums' extinction. They appeared during a tumultuous time in the late Eocene when the climate dramatically shifted form a hot humid world to the icehouse world of today. This lead to the loss of the wet forested environments that covered much of Earth and the rise of grasslands and eventually the Savannahs of the Miocene.

Luckily, Arsinoitherium's small range in North Africa and the Arabian Peninsula was initially spared this loss of forested environments. However, as the Oligocene progressed and the cool trend persisted, grasses continued to expand, including into Northern Africa. By the Middle Oligocene, Arsinoitheriums habitat and specialized food sources in forested and woodland environments changed to grasslands. Once its food and habitat were gone, it disappeared.

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Discovery

The first Arsinoitherium fossils were found in the Fayum (Faiyum/Fayoum) area of Egypt from the Jebel Qatrani formation by H. L. Beadnel in 1901.

In 1902 he published his findings and named the specimen Arsinoitherium zitteli. The genus name comes from Queen Arsinoe I of Egypt, whose husband Ptolemy II named the Fayum region after her. The name means Arsinoe’s Beast. The species is named in honor of the Paleontologist Karl Alfred Ritter von Zittel who was a pioneer in Egyptian Paleontology.

Arsinoitherium fossils were studied in much greater detail by Andrews in 1906. His publication "A descriptive catalogue of the Tertiary Vertebrata of the Fayûm, Egypt" is still a great resource with wonderful fossil illustrations. The book is available online here.

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Additional Images

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These are additional specimens from the digitized collection of the British Museum - Image Credit: The Trustees of the Natural History Museum, London (CC-by-4.0). Tap a thumbnail for the full image and specimen number.

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Recommended Prehistoric Mammal Books:

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Works Cited:

Clementz M. T., Holroyd P. A., and Koch P. L. (2008) Identifying aquatic habits of herbivorous mammalsthrough stable isotope analysis. Palaios,23, 574–585.

Court N. (1990) Periotic Anatomy of Arsinoitherium (Mammalia, Embrithopoda) and Its Phylogenetic Implications. Journal of Vertebrate Paleontology, 10(2), 170-182. Retrieved from www.jstor.org/stable/4523315

Court N. (1992b) A unique form of dental bilophodonty and a func-tional interpretation of peculiarities in the masticatory systemof Arsinoitherium (Mammalia, Embrithopoda). HistoricalBiology,6,91–111

Sanders W., 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. Link to Paper

Witton, M. (2017, September 24) The horns of Arsinoitherium: covered in skin or augmented with keratin sheaths? Retrieved from markwitton.com - blog.

Bennett S.C. (2003) New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Paläontologische Zeitschrift, 77: 61-75.

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