Thescelosauridae Sternberg, 1937

Poole, Karen E., 2016, Phylogeny of iguanodontian dinosaurs and the evolution of quadrupedality, Palaeontologia Electronica (a 30) 25 (3), pp. 1-65 : 16

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).

Figures

FIGURE 6. Parsimony (left) and Bayesian (right) trees plotted together. Strict consensus of 84 MPTs after pruning Oryctodromeus, Atlascopscosaurus, Planicoxa, Cumnoria, Cedrorestes, and NHMUK R28860. Jackknife values above 20 (with 10% chance of character removal) are shown above and to the left of their respective nodes. Bremer supports above one are shown below and to the left of their respective nodes, and bolded. CI=0.272, RI=0.634. Maximum clade credibility tree produced by Bayesian analysis showing posterior probabilities below and to the right of their respective node.

FIGURE 7. Time scaled parsimony tree, showing assigned age ranges and broad-scale geographic data. Jackknife values above 20 (with 10% chance of character removal) are shown above and to the left of their respective nodes. Bremer supports above one are shown below and to the left of their respective nodes, and bolded.

FIGURE 8. Maximum Clade Credibility tree produced by Bayesian analysis. Posterior probabilities are shown to the left of their nodes. The geologic timescale is shown across the top. Tips represent the average age found for each OTU across all sampled trees.