Читать книгу Hadrosaurs - David A. Eberth - Страница 75

The new information on the anatomy of Equijubus presented here allows its phylogenetic placement to be more confidently tested. Previous phylogenetic analyses have recovered Equijubus in a variety of positions. The analysis by You, Luo, et al. (2003) in the original description of Equijubus found it to be the most basal hadrosauroid, more derived than Iguanodon, Ouranosaurus, Altirhinus, and Jinzhousaurus, but more basal than Probactrosaurus. In contrast, the analysis of Norman (2002) placed Equijubus (referred to as “Mazongshan sp.”) in a much more basal position – basal to Iguanodon, Mantellisaurus, Ouranosaurus, and Altirhinus, and in a polytomy with Lurdusaurus. However, Norman (2002) did not code Equijubus for any postcranial characters; 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.