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.
Dinosaur
The earliest remains of a syrinx, which has enough mineral content for fossilization, was found in a specimen of the duck-like "Vegavis iaai" dated 69-66 million year ago, and this organ is unlikely to have existed in non-avian dinosaurs. However, in contrast to Senter, the researchers have suggested that dinosaurs could vocalize and that the syrinx-based vocal system of birds evolved from a larynx-based one, rather than the two systems evolving independently. A 2016 study suggests that dinosaurs produced closed mouth vocalizations like cooing, which occur in both crocodilians and birds as well as other reptiles. Such vocalizations evolved independently in extant archosaurs numerous times, following increases in body size. The crests of the Lambeosaurini and nasal chambers of ankylosaurids have been suggested to function in vocal resonance, though Senter states that the presence of resonance chambers in some dinosaurs is not necessarily evidence of vocalization as modern snakes have such chambers which intensify their hisses.