Alioramus
From Wikipedia, the free encyclopedia
 |
||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
||||||||||||||||||||
|
Extinct (fossil)
|
||||||||||||||||||||
| Scientific classification | ||||||||||||||||||||
|
||||||||||||||||||||
|
|
||||||||||||||||||||
| Alioramus remotus Kurzanov, 1976 |
Alioramus (IPA: /ˌælɪəˈɹeɪməs/; "different branch") is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Mongolia. It was smaller than its gigantic relatives Tyrannosaurus rex and Tarbosaurus, although the only known specimen is a juvenile, so estimating an adult size is difficult. It is best known for the row of six prominent bony crests on the top of its long snout.
This dinosaur was named and originally described by Russian paleontologist Sergei Kurzanov in 1976. As originally restored, the crests and low profile of the skull of this dinosaur looked so different from other tyrannosaurids that it received the name Alioramus, from the Latin alias ("other") and ramus ("branch") This refers to Kurzanov's belief that Alioramus belonged to a new and different branch of tyrannosaurid evolution. Similarly, the name of the one known species (A. remotus) also refers to its distinctiveness, being Latin for "removed."[1]
As indicated by its name, Alioramus was originally believed to be far removed from other tyrannosauroids. However, several recent analyses have placed it closer to more well-known genera within the family Tyrannosauridae. A 2004 cladistic analysis finds two equally well-supported positions for Alioramus, either just outside Tyrannosauridae, or inside of it, within the subfamily Tyrannosaurinae.[2] Other studies support the latter hypothesis, furthermore placing Alioramus as the sister taxon to Tarbosaurus within the Tyrannosaurinae.[3][4]
Remains of Alioramus were collected in the Beds of Nogoon Tsav in the Mongolian Bayankhongor Province. This geologic formation has not been extensively surveyed for dinosaur fossils, and Alioramus is the only known dinosaur found in it so far. It may belong to the Maastrichtian stage of the Late Cretaceous Period.[1] This faunal stage occurred about 74 to 65 million years ago.
Alioramus is not well-known, with only a partial skull and 3 metatarsals available to science. The skull is about 18 inches (45cm) long and low in profile, although not as low as restored in the original description, with six distinctive bony crests lined up in a row where the nasal bones meet on top of the snout.[5] Many tyrannosaurids have bumpy nasals, but none have crests as well-developed as seen in Alioramus, although the newly-described Appalachiosaurus has a row of six much lower bumps.[6] Alioramus is also characterized by a high tooth count in both upper and lower jaws. The one known specimen exhibits 16 teeth in the maxilla (upper jaw bone) and 18 in the dentary (lower jaw bone), more than any other known tyrannosaurid.
The known specimen of Alioramus is not fully grown, and allow for the possibility that it may be a juvenile of another Asian tyrannosaurid such as Tarbosaurus. However, the higher tooth count and prominent crests make this unlikely.[3]
[edit] References
- ^ a b Kurzanov, S.M. (1976). [A new Late Cretaceous carnosaur from Nogon-Tsav, Mongolia.] Journal of the Soviet-Mongolian Paleontological Expeditions 3:93-104. [in Russian]
- ^ Holtz, T.R. (2004). Tyrannosauroidea. In: Weishampel, D.A., Dodson, P., and Osmolska, H. (Eds.). The Dinosauria (2nd Edition). University of California Press:Berkeley, 111-136. ISBN 0-520-24209-2
- ^ a b Currie, P.J., Hurum, J.H., and Sabath, K. 2003. Skull structure and evolution in tyrannosaurid phylogeny. Acta Palaeontologica Polonica 48(2):227-234.
- ^ Xu X., Norell, M.A., Kuang X., Wang. X., Zhao Q., and Jia C. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature 431:680-684.
- ^ Currie, P.J. (2003). Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica 48(2):191–226.
- ^ Carr, T.D., Williamson, T.E., and Schwimmer, D.R. (2005). A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama. Journal of Vertebrate Paleontology 25(1):119-143.
