dental alveolus found on Sinosaurus is the first documented dental pathology found on a dinosaur. Paleoecology Provenance and occurrence The type specimen of Sinosaurus triassicus IVPP V34 was recovered in the Zhangjiawa Member of the Lufeng Formation, in Yunnan, China. These remains were discovered at the Dark Red Beds that were deposited during the Sinemurian stage of the Jurassic period, approximately 196-183 million years ago. Several other discoveries referred to Sinosaurus were made in the Zhangjiawa Member: specimens IVPP V97 (postcrania), IVPP V36 (teeth), IVPP 37 (teeth), IVPP V88 (ilium), IVPP V35 (teeth and postcranial bones), IVPP V100 and IVPP V48 (teeth and postcranial bones) discovered in 1938 by M. Bien & C.C. Young, FMNH CUP 2001–2003 discovered by E. Oehler and Hu. Specimens FMNH CUP 2097, FMNH CUP 2098, FMNH CUP 2004, FMNH CUP 2005 were discovered in 1948 by M. Bien & C.C. Young at Zhangjiawa Member, as well. Sinosaurus sp. fossils have been found in the Zhenzhuchong Formation, and were previously thought to be a poposaur, although they might have only been from the equivalent Lufeng Formation. Specimen IVPP V504, referred to Sinosaurus, a maxilla with four teeth, was collected by Lee in the 1940s, in the Dull Purplish Beds of Shawan Member of the Lufeng Formation, that were deposited during the Hettangian stage of the Jurassic period, approximately 201-199 million years ago. Several other discoveries were made in the Shawan Member: parts of two skeletons attributed to Sinosaurus were discovered by Sou in 1956, specimen IVPP V279 (tooth) was discovered by C.C. Young in 1938, in dark red clayish sandstone, and specimen IVPP V381 (several teeth) was discovered by C.C. Young, in blue mudstone. The D. sinensis remains, KMV 8701, a nearly complete skeleton, now referred to Sinosaurus, were recovered in the Shawan Member of Lufeng Formation. This material was discovered in 1987 in the Dull Purplish Beds that were deposited during the Hettangian stage of the Early Jurassic, approximately 201-199 million years ago. Fauna and habitat In the Lufeng Formation, Sinosaurus shared its paleoenvironment with therapsids like Morganucodon, Oligokyphus, and Bienotherium; archosaurs like Pachysuchus; diapsids like Strigosuchus; crocodylomorphs like Platyognathus and Microchampsa; the early mammal Hadrocodium; and other early reptiles. Contemporary dinosaurs include indeterminate sauropods; the early thyreophorans Bienosaurus lufengensis and Tatisaurus oehleri; the supposed chimeric ornithopod "Dianchungosaurus lufengensis"; the prosauropods Gyposaurus sinensis, Lufengosaurus huenei, L. magnus, Jingshanosaurus xinwaiensis, Kunmingosaurus wudingensis, Chinshakiangosaurus chunghoensis, Yunnanosaurus huangi,