Avimimus

Taxobox
name = "Avimimus"
fossil_range = Late Cretaceous


image_width = 200px
image_caption = Mounted skeleton of "Avimimus portentosus".
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
infraordo = Oviraptorosauria
familia = Avimimidae
familia_authority = Kurzanov, 1981
genus = "Avimimus"
genus_authority = Kurzanov, 1981
subdivision_ranks = Species
subdivision ="A. portentosus" Kurzanov, 1981 (type)

"Avimimus" (pronEng|ˌeɪvɨˈmaɪməs AY-vi-MYE-mus) meaning "bird mimic", because it resembled a bird (Latin "avis" = bird + "mimus" = mimic) was a genus of birdlike dinosaur that lived in the late Cretaceous in what is now Mongolia, around 75 million years ago.

Description

"Avimimus" was a small dinosaur, standing about 45 centimeters (2.5 ft) tall at the hipsFact|date=July 2008 and a length of 1.5 m (5 ft). The skull was relatively small compared to the body, though the brain and eyes were relatively large. The size of the bones which surrounded the brain and were dedicated to protecting it are large. This is also consistent with the hypothesis that "Avimimus" had a proportionally large brain.

As in the related Oviraptoridae and Caenagnathidae, the jaws of "Avimimus" formed a parrot-like beak, and lacked teeth. However, a series of toothlike projections along the tip of the premaxilla would have given the beak a serrated edge. The toothless beak of "Avimimus" suggests that it may have been an herbivore or omnivore. Kurzanov himself, however, believed that "Avimimus" was an insectivore.

The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in "Avimimus". The occipital condyle, however, was small, further suggestive of the skull's relative lightness. The neck itself was long and slender, and is composed of vertebrae are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that "Avimimus" is more primitive than these animals.

The forelimbs were relatively short. The bones of the hand were fused together, as in modern birds, and a ridge on the ulna (lower arm bone) was interpreted as an attachment point for feathers by Kurzanov.Kurzanov, S.M. (1981). "An unusual theropod from the Upper Cretaceous of Mongolia Iskopayemyye pozvonochnyye Mongolii (Fossil Vertebrates of Mongolia)." "Trudy Sovmestnay Sovetsko-Mongolskay Paleontologiyeskay Ekspeditsiy" ("Joint Soviet-Mongolian Paleontological Expedition"), 15: 39-49. Nauka Moscow, 1981] Kurzanov, in 1987, also reported the presence of quill knobs,Kurzanov, S.M. (1987). "Avimimidae and the problem of the origin of birds." "Transactions of the Joint Soviet-Mongolian Paleontological Expedition", 31: 5-92. [in Russian] ] and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear.Chiappe, L.M. and Witmer, L.M. (2002). "Mesozoic Birds: Above the Heads of Dinosaurs." Berkeley: University of California Press, 536 pp. ISBN 0520200942] Kurzanov was so convinced they were attachment points for feathers that he concluded that "Avimimus" may have been capable of weak flight. This interpretation has not seen wide support among paleontologists, however.

The ilium was almost horizontally oriented, resulting in exceptionally broad hips. Little is known of the tail but the hip suggests that the tail was long. The legs were extremely long and slender, suggesting that "Avimimus" was a highly specialized runner. The proportions of the leg bones add further weight to the idea of "Avimimus" was quick on its feet. The animal's shins were long in comparison with its thighs, a trait common among cursorial animals. It also had three-toed feet with narrow pointed claws.

Discovery and species

Its remains were discovered in the Djadokta Formation by Russian paleontologists,"Avimimus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. "The Age of Dinosaurs". Publications International, LTD. p. 130. ISBN 0-7853-0443-6.] and officially described by Dr. Sergei Kurzanov in 1981. The type species is "A. portentosus". Because no tail was found with the original find, Dr. Kurzanov mistakenly concluded that "Avimimus" lacked a tail in life. However, subsequent "Avimimus" finds containing caudal vertebrae have confirmed the presence of a tail.

In 1991, Sankar Chatterjee erected the Order Avimimiformes to include "Avimimus", though this group is not used by most paleontologists today as it includes only a single species.

References

External links

* [http://www.dinodata.org/index.php?option=com_content&task=view&id=711&Itemid=67 "Avimimus"] at DinoData
* [http://mijnposter.nl/thumbs/644/053s.jpeg "Avimimus portentosus" reconstruction.]
* [http://www.gondwanastudios.com/info/avi.htm "Avimimus portentosus skeleton"]