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

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The Skull of Yunnanosaurus Huangi Young, 1942 (Dinosauria: Prosauropoda) from the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China Blackwell Publishing LtdOxford, UKZOJZoological Journal of the Linnean Society0024-4082© 2007 Natural History Museum, London; Journal compilation © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society? 2007 1502 319341 Original Articles SKULL OF YUNNANOSAURUSP. M. BARRETT ET AL. Zoological Journal of the Linnean Society, 2007, 150, 319–341. With 10 figures The skull of Yunnanosaurus huangi Young, 1942 (Dinosauria: Prosauropoda) from the Lower Lufeng Formation (Lower Jurassic) of Yunnan, China PAUL M. BARRETT FLS1*, P. UPCHURCH FLS2, X.-D. ZHOU3 and X.-L. WANG4 1Department of Palaeontology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK 2Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK 3Nanjing Geological Museum, 700 Zhujian Road, Nanjing 210018, China 4Institute of Vertebrate Paleontology and Paleoanthrolopogy, Academia Sinica, PO Box 643, Beijing 100044, China Received July 2005; accepted for publication August 2006 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 inter- narial 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. © 2007 Natural History Museum, London. Journal compilation © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 150, 319–341. ADDITIONAL KEYWORDS: basal Sauropodomorpha – cranial morphology – palaeobiology – phylogenetics. INTRODUCTION Recent reviews of the group recognize around 30 pro- visionally valid taxa in the Late Triassic–Early Juras- Late Triassic and Early Jurassic terrestrial biomes sic interval (e.g. Galton & Upchurch, 2004; Upchurch, hosted a diverse array of sauropodomorph dinosaurs, Barrett & Dodson, 2004). Early sauropodomorphs including basal sauropods (e.g. Isanosaurus and Vul- ranged in size from small bipeds (1.5–2 m in length, canodon), prosauropods (e.g. Plateosaurus and Lufen- e.g. Thecodontosaurus) to large quadrupeds (10–14 m gosaurus), and basal forms that lie outside of the in length, e.g. Riojasaurus and Gongxianosaurus). prosauropod/sauropod clade (e.g. Saturnalia and The- Some taxa were probably omnivorous (Barrett, 2000), codontosaurus). Sauropodomorphs were the dominant whereas others were obligate high-fibre herbivores large animals in these ecosystems, accounting for up representing the first major radiation of herbivorous to 95% of the standing vertebrate biomass (Galton, dinosaurs (Bakker, 1978; Galton, 1985a, 1986; Cromp- 1985a, 1986), and achieved a global distribution (with ton & Attridge, 1986; Barrett & Upchurch, 2007). Sev- the exception of Australia; Weishampel et al., 2004). eral species (e.g. Plateosaurus, Massospondylus, and Thecodontosaurus) are known from multiple speci- *Corresponding author. E-mail: [email protected] mens, including complete skulls and skeletons, and © 2007 Natural History Museum, London 319 Journal compilation © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 150, 319–341 320 P. M. BARRETT ET AL. material is often well preserved and locally abundant Formation (a conclusion followed by Galton, 1976), (Galton & Upchurch, 2004). whereas Cooper (1981) proposed that Yunnanosaurus Although it is generally accepted that prosauropods was synonymous with Massospondylus, a prosauropod and Sauropoda constitute the monophyletic clade Sau- from the Lower Jurassic of southern Africa. In con- ropodomorpha (e.g. Gauthier, 1986; Sereno, 1999), the trast, most other authors have retained Yunnanosau- interrelationships of prosauropods and basal sauro- rus as a distinct taxon (Steel, 1970; Galton, 1990; pods are controversial. Pre-cladistic studies generally Galton & Upchurch, 2004; Barrett, Upchurch & Wang, concluded that at least some prosauropods were 2005). Yunnanosaurus has been included in several ancestral to sauropods, with the latter exhibiting cladistic analyses of sauropodomorph interrelation- trends towards increased body size, quadrupedality, ships (Sereno, 1999; Yates, 2003a; Galton & Upchurch, and neck elongation (e.g. Romer, 1956; Charig, 2004; Upchurch et al., 2007; Yates, 2007), but was Attridge & Crompton, 1965). Prosauropod paraphyly omitted from the analysis of Benton et al. (2000) was supported by the first cladistic analysis of the because these authors questioned the validity of the group (Gauthier, 1986), but since that time various genus. Here, we present a detailed re-description of authors have argued that prosauropods form the the skull of Y. huangi and use these new anatomical monophyletic sister group of sauropods (e.g. Galton, data to address the phylogenetic position of the taxon. 1990; Gauffre, 1993; Sereno, 1999). Recent discoveries A list of institutional abbreviations is given in of new Late Triassic sauropodomorph taxa, including Appendix 1, and a list of abbreviations used in the fig- the early sauropod Isanosaurus (Buffetaut et al., ures is given in Appendix 2. 2000) and the basal sauropodomorph Saturnalia (Langer et al., 1999), have contributed significantly to this debate. Re-interpretations of previously described SYSTEMATIC PALAEONTOLOGY taxa, including the recognition that at least some DINOSAURIA OWEN, 1842 ‘prosauropods’ are probably early sauropods (e.g. SAURISCHIA SEELEY, 1887 Anchisaurus, Antetonitrus, and Blikanasaurus), have SAUROPODOMORPHA VON HUENE, 1932 also had a major effect on our understanding of char- PROSAUROPODA VON HUENE, 1920 acter evolution in the group, and on the topology of YUNNANOSAURUS YOUNG, 1942 sauropodomorph cladograms (Benton et al., 2000; TYPE SPECIES. YUNNANOSAURUS HUANGI Yates, 2003a, 2004; Yates & Kitching, 2003; Galton & YOUNG (1942) Upchurch, 2004; Upchurch, Barrett & Galton, 2007; Yates 2007). Nevertheless, controversy still surrounds Emended diagnosis: As for type species (see below). the precise interrelationships of many basal sau- Distribution: Dark Red Beds of the Lower Lufeng For- ropodomorph taxa: some authors suggest that the mation (Lower Jurassic), Lufeng County, Yunnan majority of prosauropods form a pectinate array of Province, China. taxa with respect to sauropods (e.g. Yates, 2003a, 2004; Yates & Kitching, 2003; Yates 2007), whereas Comments: Young (1951) erected a second species, others place most prosauropods within a monophyletic Yunnanosaurus robustus, based on a partial skeleton clade (e.g. Benton et al., 2000; Galton & Upchurch, including cranial remains (IVPP V94). Although Steel 2004; Upchurch et al., 2007). Part of this conflict stems (1970) regarded Y. huangi and Y. robustus as separate from the fact that many basal sauropodomorph taxa valid species, most authors have regarded the latter as are known from incomplete material or have not yet either a junior subjective synonym of Y. huangi (e.g. been fully described. Galton, 1990; Galton & Upchurch, 2004) or L. huenei One such taxon is Yunnanosaurus huangi Young, (e.g. Rozhdestvensky, 1965). In order to stabilize the 1942 from the Lower Lufeng Formation (Lower Juras- genus, we base our diagnosis of Yunnanosaurus on the sic) of Yunnan, south-western China. Although the type species only. The validity of Y. robustus and its holotype of Y. huangi consists of an almost complete referral to Yunnanosaurus will be addressed else- skull and postcranial skeleton, it has not been studied where. in detail since the initial, rather brief, description was published over 60 years ago. Nevertheless, Yunnano- YUNNANOSAURUS HUANGI YOUNG, 1942 saurus has been discussed in a number of taxonomic 1942 Y. huangi (Young, 1942: 64, figs 1–17). and systematic publications during this interval, 1965 L. huenei Young, 1941 (Rozhdestvensky, 1965: although few authors have had the opportunity to 103). examine the material first-hand. Rozhdestvensky 1970 Y. huangi (Steel, 1970: 52). (1965) regarded Yunnanosaurus as a junior subjective 1981 Massospondylus huenei, Young, 1941 (Cooper, synonym of Lufengosaurus huenei Young, 1941, a sec- 1981: 804). ond basal sauropodomorph from the Lower Lufeng 1990 Y. huangi (Galton, 1990: 335). © 2007 Natural History Museum, London Journal compilation © 2007 The Linnean Society of London, Zoological Journal
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