Limusaurus

Limusaurus Temporal range: Late Jurassic
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Infraorder:	Ceratosauria
Genus:	Limusaurus Xu et al., 2009
Species
C. inextricabilis (type) Xu et al., 2009

Limusaurus ("mud lizard") is a genus of toothless herbivorous theropod dinosaur from the Jurassic (Oxfordian stage) upper part of the Shishugou Formation in the Junggar Basin of western China.

Description

The only species, L. inextricabilis has been described in a 2009 paper coauthored by X. Xu, J. M. Clark, J. Mo, J. Choiniere, C. A. Forster, G. M. Erickson, D. W. E. Hone, C. Sullivan, D. A. Eberth, S. Nesbitt, Q. Zhao, R. Hernandez, C.-K Jia, F.-L. Han, and Y. Guo. It is known by two young adult specimens, the holotype being an almost complete articulated skeleton, the other only missing the skull.

Limusaurus had a small slender body measuring about 1.5 m in length. It is the first definite ceratosaur from eastern Asia to be discovered and one of the earliest. Its discovery shows that the Asian dinosaurian fauna was less endemic during the Middle/Late Jurassic period than previously thought and suggests a possible land connection between Asia and other continents during that period.

Paleobiology

Limusaurus shares several cranial features with other ceratosaurs and coelophysids but display some unique characteristics for the group, such as absence of teeth and the presence of a fully developed rhamphotheca which have been previously reported in non-avian theropods only among the cretaceous coelurosaurs. Limusaurus has a long neck, short forelimbs and elongated hindlimbs indicating strong cursorial capabilities. The presence of gastroliths in the stomach of both specimens and the toothless beak indicate a herbivorous diet, previously unknown among the ceratosaurs. The overall aspect of the animal is very similar to the one of the cretaceous ornithomimid theropods and of the triassic non-dinosaurian archosaur Effigia and represents a remarkable case of convergent evolution among three distinct group of archosaurs.

Limusaurus was a very basal ceratosaur characterized by hands retaining four digits (I-IV), digit I being strongly reduced. It was traditionally thought that the hands of dinosaurs evolved into the wings of birds by the disappearance of the two outward digits (IV and V), in contradiction with developmental and ontologic studies on birds that showed that the retained digits are the three middle ones (II-III-IV). The hand structure of Limusaurus with its reduced digit I adds more weight to the digit II-III-IV identities for avian theropods and birds.