Sinosauropteryx prima (Ji and Ji 1996; Currie and Chen 2001, Early Cretaceous, Yixian Formation) is considered to have very primitive feathers. The rostrum is relatively short. The dorsal vertebrae are robust. The tail is quite long and gracile. The humerus is short and robust. The elbow (ulna) and manual digit 1 are both robust. The hind limbs are relatively shorter and robust.

Sinosauropteryx 3.8m specimen (not yet described; Early Cretaceous, Yixian Formation) images of this specimen appeared on a theropod blog post, purporting to be an adult version of the holotype Sinopteryx prima specimens. The hand and foot are distinct from the holotype. The tail is shorter. The hind limb is relatively longer, more typical of theropod proportions. The premaxilla is robust with hyper-robust premaxillary teeth. The anterior dentary is a fang.

Ji Q and Ji S-A 1996. On the Discovery of the earliest fossil bird in China (Sinosauropteryx gen. nov.) and the origin of birds. Chinese Geology 233:30-33.

Currie PJ and Chen PJ 2001. Anatomy of Sinosauropteryx prima from Liaoning, northeastern China. Canadian Journal of Earth Sciences, 38: 705-727.

wiki/Sinosauropteryx