Phylogeny of iguanodontian dinosaurs and the evolution of quadrupedality Author Poole, Karen E. text Palaeontologia Electronica 2016 a 30 25 3 1 65 http://dx.doi.org/10.26879/702 journal article 10.26879/702 1094-8074 11063310 Thescelosauridae Sternberg, 1937 Phylogenetic definition. All neornithischians more closely related to Thescelosaurus neglectus Gilmore, 1913 than to Hypsilophodon foxii Huxley, 1869 , Dryosaurus altus ( Marsh, 1878 ) , or Parasaurolophus walkeri Parks, 1922 . Unambiguous synapomorphies. In the parsimony analysis ( Figure 7 ), thescelosaurids are characterized by three unambiguous synapomorphies: dentary tooth row straight in dorsal view (98.0), 10-12 ridges on the maxillary teeth (136.3), and acromion process of scapula does not extend beyond the edge of the coracoid (196.0). In the Bayesian analysis ( Figure 8 ), a more extensive Thescelosauridae is characterized by two unambiguous synapomorphies: 10-12 ridges on the maxillary teeth (136.3) and 9-11 ridges on the dentary teeth (137.3). Topology. Thescelosauridae is recovered in the parsimony analysis ( Figures 6 , 7 ) containing Thescelosaurus , Parksosaurus , Orodromeus , and Zephyrosaurus , though the group has poor support (Jackknife value=7). Unlike in Boyd (2012) , Haya is recovered at a node basal to thescelosaurids, rather than within the Thescelosaurinae. Macrogryphosaurus and Talenkauen , which Boyd also found within Thescelosaurinae, are recovered within iguanodontia, based on the presence of opisthocoelus cervical vertebrae, and a postacetabular process that is less than 30% of total ilium length. In the Bayesian analysis ( Figures 6 , 8 ), Thescelosauridae is nested within a larger Hypsilophodontidae . Though it only has moderate support (PP=0.59), the internal nodes have higher posterior probabilities. The genera included in this group match those recovered in the parsimony analysis; the one difference in topology is that Orodromeus and Zephyrosaurus form successive outgroups to Thescelosaurus + Parksosaurus instead of forming a distinct Orodrominae (as found by Boyd 2012 ). Though Haya and Macrogryphosaurus are recovered as closely related hypsilophodontids, they are not found within Thescelosauridae as proposed in Boyd (2012) .