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293 19 19.1. A, Bolong yixianensis, YHZ-001 (holotype). Skull and partially articulated postcranial skeleton, as discovered, in right lateral view. Abbreviations: L, left; R, right. B, Skull reconstruction in left lateral view. Anatomy and Relationships of Bolong yixianensis, an Early Cretaceous Iguanodontoid Dinosaur from Western Liaoning, China Wu Wenhao* and Pascal Godefroit The skeleton (YHZ-001) of a new basal iguanodontoid was discovered in the middle part of the Yixian Formation in western Liaoning, China. Bolong yixianensis Wu, Godefroit, and Hu, 2010, is characterized by cranial, dental, and postcranial autapomorphies, as well as a unique combination of characters. A phylogenetic analysis reveals that Bolong is the most primitive Hadrosauroidea described so far. During the Lower Cretaceous, Iguanodontoidea were subdivided into Iguanodontidae, which mainly occupied Neopangean territories, and Hadrosauroidea in Asia. The presence of Iguanodontoidea in the middle part of the Yixian Formation indicates that connections between Asia and western North America and/or Europe were already established during or before the Barremian. Iguanodontoidea (=Hadrosauriformes sensu Sereno, 1997) is defined as Iguanodon, Parasaurolophus, their most recent common ancestor, and all descendants (Sereno, 1998, amended). During the Early Cretaceous, iguanodontoids had achieved a pan-Laurasian distribution and were also represented in Africa (Norman, 2004). During the Upper Cretaceous, advanced Iguanodontoidea, or Hadrosauridae (a node-based taxon defined as the most recent common ancestor of Bactrosaurus and Parasaurolphus, plus all the descendants of this common ancestor; see Norman, 2004, fig. 11.22), replaced basal iguanodontoids and became the most diverse and abundant large vertebrates of Laurasia during the Campanian and the Maastrichtian. Many new basal iguanodontoids were described during the 2000s, most of which have been recovered from Early Cretaceous deposits in China and Mongolia, including Altirhinus kurzanovi, from Khuren Dukh (late Aptian–Early Albian) of Mongolia (Norman, 1998), “Probactrosaurus” mazongshanensis and Equijubus normani, from the Ximinbao Group (Aptian– Albian) of Gansu province (Lü, 1997; You et al., 2003b), Jintasaurus meniscus , from the Xinminpu Group (?Albian) of Gansu province (You and Li, 2009), Nanyangosaurus zhugeii, from the Sangping Formation (?Albian) of Henan province (Xu et al., 2000), and Penelopognathus weishampeli, from the Bayan Gobi Formation (Albian, Lower Cretaceous) of Inner Mongolia (Godefroit et al., 2005). Lanzhousaurus magnidens, represented by an incomplete skeleton from the Hekou Group (Early Cretaceous) of Gansu province, may represent a more basal iguanodontian (You et al., 2005). Introduction Wu and Godefroit 294 The Early Cretaceous Jehol Biota of western Liaoning province in China is famous for its abundant, extraordinarily diversified, and exquisitely preserved fossils. The dinosaur fauna of the Jehol Biota is dominated by small-bodied taxa (0.2), and the articular surface for the scapula is longer than the glenoid. In hadrosaurids, the coracoid is proportionally shorter (coracoid/ scapula lengths 2 in Tethyshadros and in some hadrosaurines (e.g., Gryposaurus, Edmontosaurus, and Anatotitan) as a result of elongation of the postacetabular process of these taxa (Dalla Vecchia, 2009, fig. 5B). The dorsal edge of the postabular process is straight; however, the postacetabular notch is much deeper than in Iguanodon, Mantellisaurus, Ouranosaurus, Altirhinus, Bactrosaurus, and Tethyshadros. The main body of the ilium is about two times higher than the postacetabular process. Although it is crushed, its dorsal margin is convex in lateral view, without a distinct depression over the supracetabular process as is usually observed in hadrosaurids. The supracetabular process is poorly developed. The ventral part of the ilium (including the ischiac and pubic peduncles) is destroyed. The preacetabular process is also incompletely preserved. It is robust and weakly deflected ventrally, with a thick dorsal border. Ischium. The proximal end of the ischium is dorsoventrally expanded, transversely flattened, and triradiate, formed by an iliac ramus, a pubic ramus, and an obturator process (Fig. 19.10). The iliac ramus is the largest. Its dorsal end is thickened laterally and rugose, and it abuts the ischial peduncle of the ilium. The pubic ramus is also transversely compressed and hatchet shaped. A large triangular oburator process is present on the ventral side of the proximal portion of the ischial shaft. The salient and thin caudoventral corner of the pubic ramus and the obturator process enclose a deep obturator notch. The semicircular shape of this notch closely resembles the condition that can be observed in Altirhinus, Probactrosaurus, Bactrosaurus , and Hadrosauridae. In Iguanodon and Tethyshadros, the obturator process is located more distally on the ventral side of the ischial shaft and the obturator notch is proportionally wider and less deep. Although it is incompletely preserved, the ischial shaft is robust, transversely compressed...

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