Sinornithomimus

Taxobox
name = "Sinornithomimus"
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
subordo = Theropoda
infraordo = Coelurosauria
familia = Ornithomimidae
genus = "Sinornithomimus"
genus_authority = Kobayashi & Lü, 2003
subdivision_ranks = Species
subdivision =
*"S. dongi" Kobayashi & Lü, 2003 (type)

"Sinornithomimus" is a genus of ornithomimid theropod dinosaur found in 1997, [Kobayashi, Y., Lü, J.−C., Azuma, Y., Dong, Z.−M., and Barsbold, R. (2001) Bonebed of a new gastrolith−bearing ornithomimid dinosaur from the Upper Cretaceous Ulansuhai Formation of Nei Mongol Autonomous Region, China. "Journal of Vertebrate Paleontology 21 (Supplement to 3)": 68–69.] in the early Late Cretaceous strata of the Ulansuhai Formation located at Alshanzuo Banner, Nei Mongol Autonomous Region, Northern China. The fossil remains consist of at least fourteen skeletons found in close association, nine of which are nearly complete and relatively uncrushed. The find was comprised of three sub-adult to adult specimens and eleven juveniles, described by Kobayashi and Lü in 2003. The unweathered state of the bones, preserved in siltstone interspersed with layers of clay and the absence of evidence for post-mortem movement, argue for a catastrophic event that killed all the individuals present in the find simultaneously and instantaneously. The generic name means “Chinese bird mimic” while the specific epithet honours the discoverer of the fossils.

"Sinornithomimus" was a two-meter-long (7 ft) ornithomimid, possessing quadrate openings, with a dividing vertical sheet of bone, included in a quadrate pit and a depression on the posterior process of the parietal bone. The herbivory of this genus is supported by the presence of gastroliths, as such stones were found forming conspicuous masses in the stomach areas of the fossil skeletons. [Kobayashi, Y., Lü, J.−C., Dong, Z.−M., Barsbold, R., Azuma, Y., and Tomida, Y. (1999) Herbivorous diet in an ornithomimid dinosaur. "Nature 402:" 480–481.] This species was gregarious, which is corroborated by the arrangement of the fossil remains in a small bonebed with the juvenile individuals being approximately of the same age. This is furthermore supported by the increase of running ability as the animal progressed in its ontogeny, thus shown in the more cursorial proportions of the adults. It is assumed by the describers that adults protected themselves and their juveniles from predators by forming familial groups.

"Sinornithomimus" was a basal ornithomimid that was considered by its describers a more derived form than "Archaeornithomimus", though more recent analyses reverse the situation. The structure of the hand is similar to that of "Archaeornithomimus" representing thus an intermediate between the primitive condition of the ornithomimosaur "Harpymimus" and the one of the more derived ornithomimids. "Sinornithomimus" renders some synapomorphies of ornithomimids plesiomorphic, while also differentiating Asian ornithomimid rhamphothecae from North American ones, based on maxillary vascular foramina found in the latter.

References

* Kobayashi, Y. and Lü, J.−C. (2003). "A new ornithomimid dinosaur with gregarious habits from the Late Cretaceous of China." "Acta Palaeontologica Polonica 48 (2):" 235–259.

Notes