Xiaosaurus ("dawn lizard", ), is a genus of small herbivore dinosaur from the middle Jurassic (approximately 170.3 to 163.5 million years ago) of what is now the Sichuan Basin of China.
Discovery and naming
In 1979 and 1980, two specimens were discovered of a small herbivorous dinosaur during excavations near
Dashanpu in
Sichuan. In 1983
Dong Zhiming and
Tang Zilu named the fossils under the
type species Xiaosaurus dashanpensis. The generic name is derived from
Chinese language xiáo, 曉, "dawn", a reference to the age of the fossil. The specific name refers to Danshanpu.
[Dong Z. & Tang Z., 1983, "New ornithopod genus from the Middle Jurassic of Sichuan Basin, China", Vertebrata PalAsiatica 21(2): 168-171]
The holotype, IVPP V6730A, was found in the lower Xiashaximiao Formation of which the age is uncertain: both the Bajocian and the Bathonian–Callovian have been proposed. It consists of a partial skeleton including a jaw fragment with a single tooth, two cervical , four caudal vertebrae, a humerus, a partial left femur and a complete right hindlimb. The paratype IVPP V6730B is a second partial skeleton including a right femur, a dorsal vertebra, two sacral vertebrae, a phalanx bones, a rib and two teeth.
In 1992 Peng Guangzhao renamed Agilisaurus multidens He & Cai 1983 (now Hexinlusaurus) into a second species of Xiaosaurus: Xiaosaurus multidens,[Peng, G.-Z., 1992, Chinese: Jurassic. Vertebrata PalAsiatica 30: 39–53] but this has not been accepted.
Description
Xiaosaurus was a small bipedal animal with an estimated length of . The femur is long.
Classification
The remains are too fragmentary to easily classify the genus. The describers assigned it both to the
Fabrosauridae and the Hypsilophodontidae, considering it an
link between
Lesothosaurus and
Hypsilophodon.
Xiaosaurus has sometimes been considered a
nomen dubium and an
incertae sedis, possibly a basal
Cerapoda or
. However, Paul Barrett
et al. in 2005 concluded it to be provisionally valid, as it possessed a single unique derived trait or
autapomorphy: a mediolaterally (seen from the front) straight humerus.
[Barrett, P.M., Butler, R.J., and Knoll, F. 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. Journal of Vertebrate Paleontology 25(4):823-834]
Notes
