The Postcranial Skeleton of the Iguanodontian Ornithopod
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Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 101, 1–25, 2010 The postcranial skeleton of the iguanodontian ornithopod Jinzhousaurus yangi from the Lower Cretaceous Yixian Formation of western Liaoning, China Xiaolin Wang1*, Rui Pan1, Richard J. Butler2* and Paul M. Barrett3 1 Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing, 100044, China Email: [email protected]; [email protected] 2 Bayerische Staatssammlung fu¨r Pala¨ontologie und Geologie, Richard-Wagner-Straße 10, 80333 Munich, Germany Email: [email protected] 3 Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK Email: [email protected] *Corresponding authors ABSTRACT: Non-hadrosaurid iguanodontians were the most diverse and abundant group of large-bodied herbivorous dinosaurs during the Early Cretaceous, and were a particularly important component of Laurasian ecosystems. Recent years have seen a dramatic increase in our knowledge of the diversity of this group, with multiple new taxa being described from northeast China. The most complete of these Chinese non-hadrosaurid iguanodontians is Jinzhousaurus yangi, from the middle part of the Yixian Formation (Lower Cretaceous: lower Aptian) of Liaoning Province. Here, we provide the first description of the relatively complete and partially articulated postcranial skeleton of the holotype of Jinzhousaurus, and provide detailed comparisons to closely related taxa. We document additional autapomorphies of Jinzhousaurus that provide strong support for the validity of this taxon. KEY WORDS: Early Cretaceous, Iguanodontia, Ornithopoda, Hadrosauridae, systematics Iguanodontia is an important clade of medium- to large- (Mateus & Antunes 2001; Dalla Vecchia 2009; Norman in bodied herbivorous ornithopod dinosaurs that includes the press), South America (e.g. Novas et al. 2004; Calvo et al. largely Late Cretaceous hadrosaurids and a series of more 2007), and Africa (Taquet & Russell 1999). However, the basal taxa Jurassic and Cretaceous taxa, including Iguanodon, greatest diversity of new taxa has been described from the Camptosaurus, Dryosaurus and Tenontosaurus (e.g., Sereno upper Lower Cretaceous deposits of northern and north- 1986, 1999; Norman 1990, 1998, 2002, 2004, in press; eastern China (Table 1, Fig. 1), including ‘Probactrosaurus’ Weishampel et al. 2003; You et al. 2003). The term ‘non- mazongshanensis (inverted commas indicate that the generic hadrosaurid iguanodontian’ will be used in the present paper attribution of this species is uncertain: Norman 2002) from the to refer to a paraphyletic assemblage of ornithopod taxa than Xinminbao Group (Barremian–Albian) of Gansu Province excludes Hadrosauridae. (Paul (2008) recently used the term (Lu¨ 1997), Equijubus normani, also from the Xinminbao Group iguanodont for a similar taxonomic grouping.) Although not a of Gansu (You et al. 2003a), Nanyangosaurus zhugeii, from monophyletic grouping, non-hadrosaurid iguanodontians rep- the Sangping Formation (?Albian) of Henan Province (Xu resent an organisational grade intermediate between hadro- et al. 2000), Penelopognathus weishampeli from the Bayan saurids and more basal ‘hypsilophodontid’ ornithopods (e.g., Gobi Formation (Albian) of Inner Mongolia (Nei Monggol Norman 2004). Non-hadrosaurid iguanodontians originated in Autonomous Province: Godefroit et al. 2005), Shuangmiaosau- the Middle Jurassic (Callovosaurus leedsi); however, as is rus gilmorei from the Sunjiawan Formation (Cenomanian– generally the case for ornithopods, they did not form a Turonian) of Liaoning Province (You et al. 2003b), and significant component of ecosystems at a global level until the Lanzhousaurus magnidens, from the Hekou Group (Lower Cretaceous (Weishampel et al. 2004). During the Early and Cretaceous) of Gansu Province (You et al. 2005). Finally, mid Cretaceous they became the most diverse and abundant Wang & Xu (2001a, b) erected Jinzhousaurus yangi on the basis group of medium to large-bodied herbivorous dinosaurs, of a nearly complete, partially articulated skull and skeleton but they declined in the Late Cretaceous as hadrosaurids collected from the middle part of the Yixian Formation (Jehol diversified (Norman 2004). Group: lower Aptian) of Liaoning Province. Jinzhousaurus In the last decade our understanding of the diversity of yangi is highly significant in that its holotype specimen is the non-hadrosaurid iguanodontians has increased dramatically, most complete non-hadrosaurid iguanodontian specimen with the description of new taxa from several continents, known from Asia. No other specimens referable to Jinzhousau- including North America (Head 1998; Kirkland 1998), Europe rus have yet been described from the Yixian Formation, 2010 The Royal Society of Edinburgh. doi:10.1017/S1755691010009266 2 XIAOLIN WANG ET AL. Figure 1 Main localities for non-hadrosaurid iguanodontians in East Asia. See Table 1 for details. Jinzhousaurus yangi is from locality 6. although indeterminate non-hadrosaurid iguanodontian sub-triangular posterior process that overlaps the frontals; remains have been reported from the overlying Jiufotang frontal unit with a ‘T’-shaped outline in dorsal view and Formation (Xu & Norell 2006). prominent, distinct postorbital processes that are offset from The original description of Jinzhousaurus focused only on the main body of the bone; laterodorsal surface of the frontal the skull (Wang & Xu 2001a, b); however, the postcranial bears an elongate shallow depression; predentary with uni- skeleton has since been prepared and is well preserved, par- lobate midline process that expands in transverse width dis- tially articulated and nearly complete. Barrett et al. (2009) tally; sternal bears a well-developed, posteriorly positioned, provided an extensive redescription of the skull of Jinzhousau- tab-like midline process that forms an angle of approximately rus, as well as a rediagnosis that focused on cranial characters. 80 degrees with the posterolateral process; manual phalanx In the present paper, the authors provide the first description III-1 is broader than long and less than 20% the length of of the postcranial skeleton and compare it in detail to other metacarpal III (modified from Barrett et al. 2009). penecontemporaneous and closely related taxa. Additional Comments. The postcranial skeleton of the holotype speci- postcranial autapomorphies that support the validity of men was unprepared at the time of the initial description and Jinzhousaurus are recognised and described. all of the diagnostic features listed were restricted to the skull Institutional abbreviations: NHMUK, Natural History (Wang & Xu 2001a, b). However, as discussed by Barrett et al. Museum, London; IRSNB, Institute Royal des Sciences (2009), most of the features mentioned in the original diagnosis Naturalle de Belgique, Brussell, Belgium; IVPP, Institute of have a much wider distribution among non-hadrosaurid Vertebrate Paleontology and Paleoanthropology, Chinese iguanodontians. Barrett et al. (2009) proposed a revised diag- Academy of Sciences, Beijing. nosis based upon cranial anatomy only, and moreover dis- cussed inaccuracies present in an emended diagnosis for the genus proposed by Paul (2008). The present authors propose 1. Systematic palaeontology two additional postcranial autapomorphies for Jinzhousaurus, which are discussed in greater detail in the text. Moreover, they Ornithischia Seeley, 1887 provide detailed comparisons to other non-hadrosaurid Ornithopoda Marsh, 1881 iguanodontian taxa for which postcranial material is known. Iguanodontia Sereno, 1986 Iguanodontoidea Cope, 1869 (sensu Norman 2002) ? Hadrosauroidea Cope, 1869 (sensu Sereno 1998) 2. Description and comparisons Jinzhousaurus yangi Wang & Xu, 2001a 2.1. Overview The skeleton was collected from a single bedding plane in a Holotype. IVPP V12691, a largely complete individual number of slabs that have subsequently been embedded in comprising the skull and most of the postcranial skeleton plaster in approximately the positions in which they were (Wang & Xu 2001a, b, figs 1, 2; Barrett et al. 2009, figs 1–3) recovered (Fig. 2). The skull slab, which also contains the first (Figs 2–9). seven cervical vertebrae, is kept separately, and a cast of this Type locality and horizon. Baitaigou, Toutai Town, Yixian slab is mounted along with the postcranial skeleton. Most of County, Liaoning Province, People’s Republic of China the postcranium is divided between two large plaster blocks (Fig. 1). The specimen comes from the Dakangpu Member containing the anterior and posterior portions of the skeleton. (equivalent to the Dawangzhangzi Bed or Member) of the In addition to the cast of the skull slab, the anterior block middle Yixian Formation (Wang & Zhou 2003), which has includes the remaining cervical vertebrae in articulation, a been dated as Lower Cretaceous (lower Aptian) in age (Smith series of disarticulated dorsal vertebral centra and some more et al. 1995; Swisher et al. 1999, 2002). complete dorsal vertebrae, a series of articulated dorsal ribs, a Revised diagnosis. Differs from all other non-hadrosaurid partial sacrum, both pectoral girdles and forelimbs, including iguanodontians in possessing the following autapomorphies: both manus, and a number of ossified tendons. The posterior large shallow fossa present on the anterior part of the maxilla block contains the posterior part of the