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.
Sinosauropteryx
The hypothesis that the structures were collagen fibers was closely analyzed and disproven by a 2017 paper published by Smithwick "et al". The integument of "Sinosauropteryx" was closely compared to less controversial evidence of collagen fibers preserved in the ichthyosaur "Stenopterygius". Although the collagen hypothesis claimed that the central shafts (rachises) of purported theropod feathers were actually misidentified examples of shaft-like collagen fibers, higher quality imagery showed that these similarities were artificial. The supposed shafts in ichthyosaur collagen were actually scratch marks, cracks, and crevasses created during preparation of one of the ichthyosaur specimens. On the other hand, the shafts in the "Sinosauropteryx" specimens were legitimate examples of fossilized structures. The collagen hypothesis also claims that "Sinosauropteryx" integument includes beaded structures similar to structures occasionally found in decaying collagen of modern sea mammals. However, this claim was also unsupported, with Smithwick "et al." finding no evidence of the beaded structures which collagen hypothesis proponents identified on the specimens. The study proposes that some areas of the fossil preserved in three dimensions cast shadows which would have resembled beaded structures in low quality photographs.