Avimimus

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Avimimus Fossil range: Late Cretaceous
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Superorder: Dinosauria Order: Saurischia Suborder: Theropoda Infraorder: Oviraptorosauria Family: Avimimidae Kurzanov, 1981 Genus: Avimimus Kurzanov, 1981
Species
A. portentosus Kurzanov, 1981 (type)

Avimimus (pronounced /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.

Contents [hide] 1 Description 2 Discovery and species 3 References 4 External links

[edit] Description

Avimimus was a small dinosaur with a length of 1.5 m (5 ft).^[1] The skull was small compared to the body, though the brain^[1] and eyes were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large.^[1] This is also consistent with the hypothesis that Avimimus had a proportionally large brain.^[1]

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.^[1]

The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus.^[1] The occipital condyle, however, was small, further suggestive of the skull's relative lightness.^[1] 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.^[2][1] Kurzanov, in 1987, also reported the presence of quill knobs,^[3][1] and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear.^[4] Kurzanov was so convinced they were attachment points for feathers that he concluded that Avimimus may have been capable of weak flight.^[1] The presence of feathers is now widely accepted, but most paleontologists do not believe Avimimus could fly.^[1]

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.^[1] The animal's shins were long in comparison with its thighs,^[1] a trait common among cursorial animals. It also had three-toed feet with narrow pointed claws.

[edit] Discovery and species

Its remains were discovered in the Djadokta Formation by Russian paleontologists,^[1] and officially described by Dr. Sergei Kurzanov in 1981. The type species is A. portentosus.^[2] Because no tail was found with the original find, Dr. Kurzanov mistakenly concluded that Avimimus lacked a tail in life.^[1] However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail.^[1]

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.

In 2008 a team of Canadian, American, and Mongolian paleontologists headed by Phil Currie reported finding an extensive bonebed of Avimimus fossils. The bonebed is in the Nemegt Formation, 10.5 meters above the Barun Goyot Formation, in the Gobi Desert. The team reported finding abundant bones of at least ten individuals of Avimimus, but the deposit may hold more. All individuals were either adult or subadult, and the adults showed little variation in size, suggesting determinant growth. The adults showed a greater degree of skeletal fusion in the tarsometatarsus and tibiotarsus, and also more prominent muscle scars. The team also suggests that the individuals were found together because they were gregarious in life.^[5]

[edit] References

1. ^ ^{a b c d e f g h i j k l m n o p} "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.
2. ^ ^{a b} 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
3. ^ 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]
4. ^ Chiappe, L.M. and Witmer, L.M. (2002). Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press, 536 pp. ISBN 0520200942
5. ^ Currie, Philip., Longrich, nicholas., Ryan, Michael., Eberth, David., Demchig, Badamgarov. (2008) A BONEBED OF AVIMIMUS SP. (DINOSAURIA: THEROPODA) FROM THE LATE CRETACEOUS NEMEGT FORMATION, GOBI DESERT: INSIGHTS INTO SOCIAL BEHAVIOR AND DEVELOPMENT IN A MANIRAPTORAN THEROPOD. Journal of Vertebrate Paleontology 28(3), Supplemental, September 2008.