Hadrosaurs. David A. Eberth
You, Luo, et al. (2003) did code Equijubus for characters related to the cervical vertebrae, sacrum, and sternal (characters 41–43 and 45), but not for characters related to the ilium and femur. A subsequent analysis of Norman (2004) placed Equijubus in the same basal position as that of Norman (2002).
Wang et al. (2010) reanalyzed the datasets of You, Luo, et al. (2003) and Norman (2004) with new information on Jinzhousaurus, and again found Equijubus to be a basal hadrosauroid and a more basal iguanodontian outside Hadrosauroidea, respectively. The analyses of Sues and Averianov (2009) and Prieto-Márquez (2010) also included Equijubus, and both found it to be a basal hadrosauroid close to Probactrosaurus gobiensis as did You, Luo, et al. (2003); however, both of these analyses focused primarily on derived hadrosauroids and hadrosaurids and incorporated only a limited sample of more basal members of Iguanodontia. Finally, the analysis of McDonald, Kirkland, et al. (2010) found Equijubus to be a basal hadrosauroid in a polytomy with Altirhinus; a clade of Jinzhousaurus plus Penelopognathus, and a clade composed of Eolambia, Probactrosaurus gobiensis, and all more derived iguanodontians. Although this analysis included an extensive sample of basal iguanodonts, Equijubus was not coded for any characters related to the pectoral girdle or femur.
3.21. Phylogenetic relationships of Equijubus normani. Time-calibrated phylogeny of basal iguanodonts using the maximum agreement subtree of McDonald (2012b). Timescale based upon Walker and Geissman (2009); numerical ages are in millions of years. Uncertainty in taxon ages indicated by lighter circles or ellipses. Modified from McDonald (2012b).
Equijubus was recently included in the global phylogenetic analysis of basal iguanodonts by McDonald (2012b). The coding of Equijubus included both cranial and postcranial features described by You, Luo, et al. (2003) and those described for the first time herein. For example, Equijubus was coded for characters related to the scapula (1011), ilium (1111, 1123, and 1140), and femur (1231, 1250, 1261, 1273, 1281, and 1330) in the analysis of McDonald (2012b); this analysis was the first to code Equijubus for all preserved postcranial characters. The maximum agreement subtree of McDonald (2012b) placed Equijubus as the sister taxon of Xuwulong (You et al., 2011), a basal hadrosauroid from the Xinminpu Group of the neighboring Yujingzi Basin (Fig. 3.21). Equijubus and Xuwulong were united by a single ambiguous synapomorphy (751: presence of a rostrocaudally directed groove on the ventral surface of the basioccipital). The clade of Equijubus plus Xuwulong was more derived than Iguanodon bernissartensis, Mantellisaurus, and Altirhinus, but more basal than “Probactrosaurus” mazongshanensis (= Gongpoquansaurus mazongshanensis [You, Li, and Dodson, this volume]), Probactrosaurus gobiensis, and Eolambia.
CONCLUSIONS
Equijubus normani is diagnosed by a suite of cranial and vertebral autapomorphies and a unique combination of characters. An enhanced diagnosis and complete description of Equijubus allow it to be readily distinguished from other basal iguanodonts, including the rapidly growing record of basal iguanodont taxa from China. The new anatomical data presented here can be used in comparisons with other iguanodonts, and incorporated into future phylogenetic analyses. Detailed osteological descriptions of existing taxa are crucial to distinguishing additional taxa and, ultimately, in fully assessing diversity of basal iguanodonts in Asia and globally.
ACKNOWLEDGMENTS
This chapter is primarily the work of the first three authors; ATM wrote the cranial description, and SCRM and PMB wrote the postcranial sections. ATM thanks M. Lamanna (CM) for access to the skull of IVPP V 12534 while it was on loan; and J. Bartlett and J. Bird (CEUM), R. Allain (MNHN), S. Chapman and L. Steel (NHMUK), and S. Shelton (SDSM) for access to comparative material. SCRM and PMB thank X. Xu, F. Zheng, and C. Sullivan (IVPP); C. Mehling (AMNH); A. Henrici (CM); D. Schwarz-Wings (MB); and M. Carrano (USNM) for access to specimens in their care; and P. Mannion (University College London) for assistance during data collection in China. We are grateful to D. Evans and D. Norman for reviews that improved the manuscript. ATM’s research was funded by grants from the Jurassic Foundation, Evolving Earth Foundation, University of Pennsylvania Paleobiology Summer Stipend, and Utah Friends of Paleontology. SCRM’s visit to China was funded by a grant from the Jurassic Foundation; visits to collections housing comparative material were funded by Natural Environment Research Council grant number NE/G001898/1 awarded to PMB. HY and PD’s work on Chinese iguanodonts is supported by National Science Foundation grant NSF EAR 1024671. HY’s work on Chinese iguanodonts is also supported by the National Natural Science Foundation of China.
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