New material of a non-averostran neotheropod dinosaur from the Lower Jurassic Lufeng Formation of Yunnan, south-western China

Abstract

Neotheropoda is the core clade of predatory dinosaurs that originated in the Triassic and became highly diversified and globally distributed by the Early Jurassic. Currently, six species of Neotheropoda have been described from Early Jurassic localities in Yunnan Province, south-western China. Here we describe a new specimen from the Lufeng Formation in central Yunnan, representing a non-coelophysoid, non-averostran neotheropod. Osteohistological analysis indicates the immaturity of the specimen. Computed tomography scans reveal the internal morphology of trunk vertebrae, implying a more developed postcranial skeletal pneumaticity in averostran-line neotheropods than previously thought. Phylogenetic analysis finds the new specimen as the closest sister-taxon to Averostra (Ceratosauria + Tetanurae). It does not form a unique subclade with the previously described Lufeng Formation taxa Shuangbaisaurus anlongbaoensis and Sinosaurus triassicus. Instead, Sh. anlongbaoensis and Si. triassicus are found as sister-taxa, indicating that the former may be a subjective junior synonym of the latter. Although the new specimen has a unique combination of character states, and a potential autapomorphy, we conservatively refrain from establishing a new taxon, due to its immature status and the lack of information on postcranial anatomy in other Yunnan theropods. Regardless, this specimen bridges a morphological gap between non-averostran and averostran theropods.