STYRACOSTERNA Sereno, 1986

Phylogenetic definition. The most inclusive clade containing Parasaurolophus walkeri Parks 1922 but not Camptosaurus dispar (Marsh, 1879) or Uteodon aphanoecetes (Carpenter and Wilson 2008) .

Unambiguous synapomorphies. Styracosterna is characterized by five unambiguous synapomorphies: presence of denticulation on the oral margin of the premaxilla (5.1), 18-28 maxillary tooth positions (123.2), dentary teeth with a maximum of two to four ridges extending from the base to the tip of the crown on lingual side of teeth (137.1), maxillary tooth crowns mesiodistally narrower than dentary crowns (149.1), mid to posterior dorsal vertebrae with length much shorter than height (164.1).

Topology. Styracosterna has strong support in both topologies (JV=35, BS=4, PP=0.91), but within this group, relationships are resolved poorly. The parsimony tree (Figure 7) has several polytomies and the Bayesian tree (Figure 8) recovers several small clades within Styracosterna, but most have low support.