Anserimimus

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Anserimimus
Fossil range: Late Cretaceous

Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Superfamily:	Ornithomimosauria
Family:	Ornithomimidae
Genus:	Anserimimus
Species:	A. planinychus

Binomial name

Anserimimus planinychus
Barsbold, 1988

Anserimimus (pronounced /ˌænsɨrɨˈmaɪməs/ AN-ser-i-MYEM-us; 'goose mimic') is a genus of ornithomimid theropod dinosaur, from the Late Cretaceous Period of what is now Mongolia. It was a lanky, fast-running animal, possibly an omnivore. From what fossils are known, it probably closely resembled other ornithomimids, except for its more powerful forelimbs.

Mongolian paleontologist Rinchen Barsbold named Anserimimus in 1988, combining the Latin anser meaning 'goose' with the Greek mimos meaning 'mimic'. Anser is the generic name of several species of geese. Although Anserimimus does not specifically resemble a goose, ornithomimosaurs have traditionally been named after different types of birds, such as Struthiomimus ('ostrich mimic'), Gallimimus ('rooster mimic'), and Pelecanimimus ('pelican mimic'). The one known species of Anserimimus is called A. planinychus, from the Latin planus meaning 'flat', and the Ancient Greek onychos meaning 'claw', in reference to the peculiar flattened claws which characterize the genus.

Anserimimus is a member of the family Ornithomimidae, a group of derived ornithomimosaurians. Its closest relative may be Gallimimus (Kobayashi & Lu, 2003; Kobayashi & Barsbold, 2005). Other studies have been unable specifically to determine its relationships or those of any other ornithomimids (Ji et al., 2003; Makovicky et al., 2004).

Both Anserimimus and Gallimimus were recovered from the Nemegt Formation of Mongolia, albeit from different areas. Anserimimus was found in the Mongolian aimag, or province, of Bayankhongor during a joint Soviet-Mongolian expedition to the Gobi Desert, in the late 1970s. The Nemegt is thought to represent alluvial plains containing meandering rivers, dating from the Maastrichtian stage of the Late Cretaceous, or about 74 to 65 million years ago. Aside from Gallimimus, other theropods from this time and place include the gigantic Tarbosaurus and Deinocheirus, as well as smaller dromaeosaurids, oviraptorosaurs, troodontids, and birds. Herbivores are represented by the hadrosaurids Barsboldia and Saurolophus, the ankylosaurid Tarchia and several titanosaurian sauropods and pachycephalosaurians.

There is only a single specimen of Anserimimus, which consists of most of a forelimb and hind limb (including parts of the shoulder and pelvis) and one back vertebra. Limited information has been published on the anatomy of Anserimimus, as Barsbold did not describe most of these bones, instead focusing on only those with features that set Anserimimus apart from other ornithomimids. There are several key differences between it and other members of its family. The claws on the hand are long and straight (not curved), with the lower surface nearly flat. The forelimb is also built more powerfully than other ornithomimids, with large crests on the scapulocoracoid of the shoulder and humerus (upper arm bone), which provided attachment points for large arm muscles like the biceps.

The function of such a powerful 'arm', with straightened claws remains unknown. It may indicate a different diet or food-gathering strategy than other ornithomimids, although its diet is difficult to determine, since the animal's skull is unknown. Scientists have long hypothesized that ornithomimids, descended from carnivorous theropod ancestors, were actually omnivores or even herbivores (Osborn, 1916). Another Mongolian ornithomimid, Gallimimus, has a comb-like structure near the tip of both upper and lower jaws, which is though to function as a filter to strain food particles out of the water, similar to anseriforms and flamingoes. As most known ornithomimids occur in environments near water, this mode of feeding may extend to all members of the family, including Anserimimus (Norell et al., 2001).

[edit] References

Barsbold, R. 1988. A new Late Cretaceous ornithomimid from the Mongolian People's Republic. Paleontological Journal 22: 124-127.
Ji Q., Norell, M.A., Makovicky, P.J., Gao K., Ji S, & Yuan C. An early ostrich dinosaur and implications for ornithomimosaur phylogeny. American Museum Novitates 3420: 1-19.
Kobayashi, Y. & Lu J. 2003. A new ornithomimid dinosaur with gregarious habits from the Late Cretaceous of China. Acta Paleontologica Polonica 48(2): 235–259.
Kobayashi, Y. & Barsbold, R. 2005. Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences 42: 1501-1521.
Norell, M.A., Makovicky, P.J., & Currie, P.J. 2001. The beaks of ostrich dinosaurs. Nature 412: 873-874.
Osborn, H.F. 1917. Skeletal adaptations of Ornitholestes, Struthiomimus, and Tyrannosaurus. Bulletin of the American Museum of Natural History 35: 733–771.