Herrera-Flores et al.—Reassessment of Clevosaurus latidens
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Figure 3. Consensus trees recovered from the phylogenetic analyses: (1) maximum parsimony 50% majority rule consensus tree; CI=0.38628, RI=0.66403; node labels denote the proportion of MPTs that recover that node; (2) 50% majority rule consensus tree from the Bayesian-inference analysis, with clade credibility values (decimal proportions) labeled on the nodes.
related to Opisthodontia, but was found in a polytomy with early-diverging rhynchocephalians such as Rebbanasaurus Evans, Prasad, and Manhas, 2001, the clade of Sphenocondor Apesteguía, Gomez, and Rougier, 2012 and Godavarisaurus Evans, Prasad, and Manhas, 2001, and the clade Eusphenodontia. Overall, the results of the Bayesian analysis (Fig. 3.2)
resemble those of the parsimony analysis, but with considerably less resolution. Several large polytomies were recovered, but where clades are resolved, the clade credibility values are often moderately high. The Bayesian 50% majority rule consensus tree also recovered Pelecymala in a polytomy with early diver- ging rhynchocephalians, which confirms that this taxon is not related to opisthodontians as previously assumed (Martínez et al., 2013; Hsiou et al., 2015). The Bayesian tree did not recover clevosaurs as a monophyletic group; all of them were recovered in a large polytomy that obscures the relationships between the taxa. Relationships among other, later-diverging rhynchocephalians are unclear; many of them are part of a polytomy that includes Fraserosphenodon, but no clevosaurs. This result confirms that Fraserosphenodon is not closely related to Clevosaurus. It should be noted that the Bayesian tree recovered a close
relationship between the extant Sphenodon and the Jurassic Cynosphenodon, a close relationship between Theretairus and Sphenovipera, and pleurosaurs as a monophyletic group. The Bayesian tree did not recover Opisthodontia as a monophyletic group, but completely agrees with the parsimony tree for the
interrelationships of eilenodontines, which are quite robust and well resolved.
Discussion
Among Mesozoic rhynchocephalians, clevosaurs were one of the most diverse groups. Clevosaurs are represented by three genera: Polysphenodon, Brachyrhinodon, and Clevosaurus. The first two genera are monospecific, whereas Clevosaurus currently has nine formally recognized species. The high diversity of the genus Clevosaurus, however, is debatable because of the doubtful validity/referral of some of the species, especially those based on poorly preserved or very fragmentary material, such as the three Chinese species (C. mcgilli, C. petilus, and C. wangi)or ‘C. latidens’ from Great Britain. According to Jones (2006a), the Chinese specimens are too poorly preserved to diagnose them as three distinct species, but clearly all of them belong to Clevosaurus. In contrast to the Chinese specimens, the referral of ‘C. latidens’ to Clevosaurus has been widely questioned (Jones, 2006a, 2009; Martínez et al., 2013; Hsiou et al., 2015; Klein et al., 2015). Before the description of ‘Clevosaurus latidens,’ specimen
AUP 11192, a dentary fragment, was tentatively related to Pelecymala based on its transversely wide teeth (Fraser, 1986). When Fraser (1993) formally described ‘C. latidens,’ he noted that the tooth morphology of the new ‘Clevosaurus’ species was quite similar to that of other taxa with transversely wide teeth such as P. robustus and Toxolophosaurus cloudi Olson, 1960
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