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.
Cynosaurus
"Cynosaurus" was first described by Richard Owen in 1876. Owen wrote and journal titled “Descriptive and illustrated catalog of the fossil reptilia of South Africa in the collection of the British Museum” in 1876. Owen named the fossil "Cynosuchus suppostus" (Owen, 1876) which later gets renamed as "Cynosaurus" by Hopson et al 1972. Owen described "Cynosuchus suppostus" as similar to "Cynochampea" in where the incisors and canines are located. The difference is that "Cynosuchus" suppostus had smaller and more upward location of nostril. The external nostril of "Cynosuchus suppostus" along with the forends of the upper and lower jaws were close in location with the nostril nearly horizontal. Owen described the molar teeth as relatively larger in size. Owen also noted the constriction of the upper jaw as it recedes and is combined with large molar teeth that shows "Cynosuchus suppostus" to have a broader and shorter skull. The nasal bones are broad and thick and overlapped by the maxillaries (Owen, 1876).