The skull of Yunnanosaurus huangi Young, 1942 (Dinosauria: Prosauropoda) from the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China

Abstract

The Lower Lufeng Formation (Lower Jurassic: ?Hettangian-?Sinemurian) of Yunnan Province, China, has yielded an important and diverse fauna of terrestrial vertebrates that is dominated by early sauropodomorph dinosaurs (prosauropods and basal sauropods). Nevertheless, few of these animals have been studied in detail, undermining their potential significance in understanding sauropodomorph phylogeny, palaeobiology, and palaeoecology. Here, we present a detailed re-description of the cranial osteology of Yunnanosaurus huangi Young, 1942 and propose an emended diagnosis for this taxon on the basis of numerous autapomorphic characters (including an expanded internarial bar, unusual midline cranial bosses, and the possession of elongate maxillary tooth crowns lacking marginal serrations). Incorporation of these novel anatomical data into existing phylogenetic analyses of sauropodomorph interrelationships substantially affects the resolution, length, and topologies of the trees recovered. Although the phylogenetic position of Yunnanosaurus remains labile, these new analyses undermine previous suggestions that the former was the sister taxon of the southern African prosauropod Massospondylus . Several features of the skull of Yunnanosaurus (small external nares, cranial bosses, tooth crown morphology, and the lack of maxillary foramina) indicate that the palaeobiology of Yunnanosaurus may have been rather different from that of other prosauropods and basal sauropods, although more detailed functional studies and better material are needed to confirm this suggestion.