Aorun
| Aorun | |
|---|---|
| |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Alvarezsauroidea (?) |
| Genus: | †Aorun Choiniere et al., 2013 |
| Type species | |
| †Aorun zhaoi Choiniere et al. 2013
| |
Aorun (
Discovery and naming
The
vertebrae and leg bones were discovered by James Clark, the Ronald B. Weintraub Professor of Biology, in the Department of Biological Sciences of GW's Columbian College of Arts and Sciences with his then doctoral student Jonah Choiniere, along with a team of international researchers in a remote region of Xinjiang in China in 2006. They originally spotted a portion of a leg bone exposed on the surface, and when they dug it up, they found the skull underneath.[3]
The
Dragon King of the West Sea in the epic Journey to the West.[1][4] The specific name honours Professor Zhao Xijin
, who led several important vertebrate paleontological expeditions
to the Junggar Basin. Aorun zhaoi is the only species under the genus, which thus is monotypic
.
Description
The
sclerotic ring which is composed of overlapping ossicles. The gracile hand of this specimen, which has particularly thin metacarpals III and IV more closely approximates the hands of derived non-avian coelurosaurs (Gishlick & Gauthier 2007) than the hands of more basal theropods.[5]
It is estimated that the number of teeth in the
dentary between twenty-five and thirty. Its twelve maxillary tooth positions is also suggestive of a juvenile condition, with adult coelurosaurs typically having 15 or more. The teeth are distinctive, because they have no serrations (in the premaxillary and in some dentary teeth), or bear very fine serrations (~10/mm) only on the distal carinae (maxillary teeth and some dentary teeth). The authors noted, however, that the variability in the dentition may represent the juvenile condition.[1]
Size and ontogenetic stage
The specimen, as can be judged from the available
type specimen is a juvenile individual and measures about 1 m (3.3 ft) long, weighing about 1.5 kilograms (3.3 lbs).[1] Choiniere et al. (2013) noted that based on a histological analysis of its femur and tibia and other characteristics of the holotype, this specimen of Aorun is at most one year old, and is clearly not a perinate
. The relatively large orbit of Aorun is not indicative of what would be expected of an adult morphology.
Diagnostic features
The describing authors established some diagnostic traits. In the depression for a skull opening, the fenestra antorbitalis, to the front a second opening is present, a fenestra maxillaris, that occupies much of the front part of this depression. The teeth in the maxilla only on their rear edges have denticles which are very small and directed towards the point of the teeth. The neck vertebrae are mildly opisthocoelous: with centra that are convex in front and concave at the rear. The claws of the hand are different from each other: the thumb claw is large and curved, but the other two claws are smaller and feature a straight underside. The shinbone has on its front outer side only a high narrow groove functioning as contact with the upper part of the astragalus. This processus ascendens however, though indeed positioned on the outer side, is low.
Aorun is different from other theropods discovered from the same region, such as neural spines are short and elongated towards the posterior in the dorsal vertebrae, and the pubic shaft is curved at the end. The limb bones are also substantially different.[1]
Phylogeny
The authors placed Aorun in a basal position in within Coelurosauria and a member of
synapomorphies that would provide evidence of its affinity with more derived coelurosaurian taxa. Tykoski (2005) and others have demonstrated that when immature taxa, as is the case with this specimen, are coded as adults in a phylogenetic analysis, the immature taxa were recovered in artificially basal positions relative to adults of the same taxon.[6][7][8] In their cladistic analysis of Bannykus and Xiyunykus, Xu et al. (2018) recovered Aorun as a basal alvarezsaur.[9] This assignment has been questioned.[10]
Paleoecology
Provenance and occurrence
The remains of the type specimen of Aorun zhaoi IVPP V15709 was recovered in the
Beijing, China.[1]
Fauna and habitat
The
mammals.[2] Aorun is the seventh theropod, and oldest coelurosaur known from the Shishugou Formation, which is considered one of the most phylogenetically and trophically diverse middle to late Jurassic theropod faunas.[1]
References
- ^ S2CID 53538348. Archived from the original(PDF) on 11 January 2019.
- ^ a b Nosowitz D (3 May 2013). "New Dinosaur Species Found In China". POPSCI. Popular Science, A Bonnier Corporation Company. Retrieved 2013-05-04.
- ^ Gatin L (3 May 2013). "George Washington University Biologist Discovers New Dinosaur in China". Media Relations. George Washington University, Washington, D.C. Archived from the original on 2014-08-12. Retrieved 2013-05-04.
- ^ George Washington University (3 May 2013). "New dinosaur fossil discovered in China: Meat-eating dinosaur from late Jurassic period was less than a year old". ScienceDaily. ScienceDaily LLC. Retrieved 2013-05-04.
- ^ Gishlick, A. D. & Gauthier, J. A. 2007. On the manual morphology of Composognathus longipes and its bearing on the diagnosis of Compsognathidae. Zoological Journal of the Linnean Society, 149, 569–581.
- ^ Tykoski, R. S. 2005. Anatomy, ontogeny, and phylogeny of coelophysoid theropods. Unpublished PhD thesis, University of Texas at Austin, 552 pp.
- ^ Kammerer, C. F. 2010. Systematics of the Anteosauria (Therapsida: Dinocephalia). Journal of Systematic Palaeontology, 9, 261–304.
- ^ Tsuihiji, T., Watabe, M., Tsogtbaatar, K., Tsubamoto, T., Barsbold, R., Suzuki, S., Lee, A. H., Ridgely, R. C., Kawahara, Y. &Witmer, L. M. 2011. Cranial osteology of a juvenile specimen of Tarbosaurus bataar (Theropoda, Tyrannosauridae) from the Nemegt Formation (Upper Cretaceous) of Bugin Tsav,
- ^ ^ Xing Xu; Jonah Choiniere; Qingwei Tan; Roger B.J. Benson; James Clark; Corwin Sullivan; Qi Zhao; Fenglu Han; Qingyu Ma; Yiming He; Shuo Wang; Hai Xing; Lin Tan (2018). "Two Early Cretaceous fossils document transitional stages in alvarezsaurian dinosaur evolution". Current Biology. Online edition. doi:10.1016/j.cub.2018.07.057.
- ISSN 0891-2963.
- PMID 31409823.
- ^ Xu, X., Clark, J. M., Mo, J., Choiniere, J., Forster, C. A., Erickson, G. M., Hone, D. W. E., Sullivan, C., Eberth, D.A., Nesbitt, S., Zhao, Q., Hernandez, R., Jia, C.-K., Han, F.-l.&Guo, Y. 2009a. A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature, 459, 940–944.
- ^ Choiniere, J. N., Clark, J. M., Forster, C. A. & Xing, X. 2010a. A basal coelurosaur (Dinosauria: Theropoda) from the Late Jurassic (Oxfordian) of the Shishugou Formation in Wucaiwan, People's Republic of China. Journal of Vertebrate Paleontology, 30, 1773–1796.
- ^ Xu, X., Clark, J. M., Forster, C. A., Norell, M. A., Erickson, G. M., Eberth, D.A., Jie, C.&Zhao, Q. 2006. Abasal tyrannosauroid dinosaur from the Late Jurassic of China. Nature, 439, 715–718.
- ^ Choiniere, J. N., Xu, X., Clark, J. M., Forster, C. A., Guo, Y. & Han, F. 2010b. A basal alvarezsauroid theropod from the early Late Jurassic ofXinjiang, China. Science, 327, 571–574.