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Changchunsaurus Temporal range: Early-Late Cretaceous, Aptian–Cenomanian PreꞒ Ꞓ O S D C P T J K Pg N
Life reconstruction of Changchunsaurus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Family:	†Thescelosauridae
Genus:	†Changchunsaurus Zan et al., 2005
Species:	†C. parvus
Binomial name
†Changchunsaurus parvus Zan et al., 2005

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Changchunsaurus (meaning "Changchun lizard") is an extinct genus of small herbivorous dinosaur from Early Cretaceous deposits of Gongzhuling, Jilin, China. It is the first named dinosaur genus from Jilin.^[1]

Changchunsaurus was first named by Zan Shu-Qin, Chen Jun, Jin Li-Yong and Li Tao in 2005. The type and only known species is C. parvus ("parvus" meaning "petite"), named for its small size. It is known from a skull and skeleton and additional skull fragments. All specimens of Changchunsaurus were collected from the Quantou Formation of the Songliao Basin, dating to the Aptian–Cenomanian stages. Changchunsaurus is based on the holotype JLUM L0403-j–Zn2, a skeleton and skull, with a premaxilla (upper beak) and partial lower jaw also known. Only the skull was figured and described in the official description.^[1]

According to Zan et al. 2005, who described it, the animal shows a combination of features like those of derived ornithopods (reduction in size or loss of some skull fenestrae or holes), and features like those of more basal ornithopods (for example, five teeth in each premaxilla, short toothless portion of upper beak, and a small gap between beak teeth and cheek teeth). There is a projection that sticks out from the side of the jugal or cheekbone, with what is described as a "nubble structure". The type individual was a small animal, around 1 meter long (3.3 feet, with a skull 11.5 centimeters long (4.5 inches). It was originally classified as a basal ornithopod, family unknown, although it was not included in a formal phylogenetic analysis.^[1]

Later, some referred specimens were described and in 2010 its cranial anatomy was revised.^[2]

In Butler et al., 2011, the postcranial osteology was described for the first time and a large phylogenetic analysis confirmed its position as a basal ornithopod which was found to be closely related to another Chinese ornithopod, Jeholosaurus^[3] and later to the newly described Chinese ornithopod Haya.^[4] Han et al. named this clade "Jeholosauridae" in 2012.^[5]

The following cladogram was based on analysis by Makovicky et al., 2011.^[4]