Redescription of the Cranium of Jingshanosaurus xinwaensis (Dinosauria: Sauropodomorpha) from the Lower Jurassic Lufeng Formation of Yunnan Province, China.

Abstract

The Lower Jurassic Lufeng Formation in Yunnan Province of southwestern China has yielded an important and diverse terrestrial vertebrate fauna dominated by basal sauropodomorph dinosaurs. Nevertheless, many of them lack detailed descriptions and/or explicit diagnoses, hampering systematic analyses of their interrelationships and further studies. We present a detailed redescription of the cranial osteology of Jingshanosaurus xinwaensis and amend its diagnosis. Incorporation of the revised anatomical data into a phylogenetic analysis finds Jingshanosaurus to be one of the earliest diverging sauropodiforms. Moreover, the previously reported Chuxiongosaurus lufengensis is considered to be a junior synonym of J. xinwaensis. Jingshanosaurus can be diagnosed by a unique combination of character states, including (1) an inflection at the base of the dorsal premaxillary process; (2) the level of the caudal margin of the external naris being caudal to the mid-length of the maxillary tooth row and the rostral margin of the antorbital fenestra; (3) a ventrally constricted subtriangular orbit; (4) the height-to-length ratio of the dentary being greater than 0.2; and (5) a distally recurved long axis of the premaxillary and rostral maxillary tooth crowns. As the largest taxon (around 9 m long) currently known among Lufeng basal sauropodomorphs and one of the best known basal-most sauropodiforms, a better understanding of Jingshanosaurus will allow for reconstruction of the ecomorphotypic diversity of the Lower Jurassic Lufeng dinosaurs and help to decipher the origin and early evolution of sauropodiforms, the clade ultimately leading to the gigantic sauropods. Anat Rec, 303:759-771, 2020. © 2019 Wiley Periodicals, Inc.