Sinosauropteryx
Three specimens have been assigned to "Sinosauropteryx prima": the holotype GMV 2123 (and its counter slab [opposite face], NIGP 127586), NIGP 127587, and D 2141. Another specimen, IVPP V14202, was assigned to the genus but not to the only species by Zhang and colleagues. The assignment of an additional larger specimen to "S. prima", GMV 2124, was later found to be in error. All of the fossils were found in the Jianshangou or Dawangzhangzi Beds of the Yixian Formation in the Beipiao and Lingyuan regions of Liaoning, China. These fossil beds have been dated to 124.6–122 million years ago, during the early Aptian stage of the Early Cretaceous.
Sinosaurus
The skull of "Sinosaurus" has a deep notch between the premaxilla and maxilla. Dong (2003) proposed that the notch was used to house jaw muscles, giving "Sinosaurus" a powerful bite. Based on the estimated power of its jaws, "Sinosaurus" might have either been a carnivore or a scavenger. Dong suspected that the premaxilla was covered in a narrow, hooked beak, that was used to rip open skin and abdominal flesh. He also thought that the crest would have been used to hold open the abdominal cavity while feeding. Dong studied the feet of "Sinosaurus" as well, finding a resemblance with the feet of modern vultures. The feet of "Sinosaurus" were probably adapted to help it feed on large-bodied animals, such as prosauropods.