DRYOSAURIDAE Milner and Norman, 1984

Phylogenetic definition. The most inclusive clade containing Dryosaurus altus (Marsh, 1878) but not Parasaurolophus walkeri Parks, 1922 (Sereno, 2005).

Unambiguous synapomorphies. Dryosauridae is characterized by nine unambiguous synapomorphies: premaxilla with a medial dorsal (nasal) process that does not contact the nasal (9.1), palpebrals that traverse the entire width of orbit (42.1), a dentary with dorsal and ventral margins (under the tooth row) that converge anteriorly (97.0), maxillary teeth with primary ridges that are centered mesio-distally (143.0), 15 or fewer dorsal vertebrae (161.0), posterior dorsal vertebrae with transverse processes longer than the dorsoventral height of the centrum (167.1), scapula with a weakly developed acromion process (195.0), prepubic process with a horizontal ridge on medial side (273.1) and a pubis with an obturator foramen completely enclosed by bone (275.0)

Topology. In addition to Dryosaurus and Dysalotosaurus, which have been found previously to form a clade (McDonald et al., 2010b), this analysis finds the unnamed Kirkwood taxon from South Africa within the group, as sister to Dysalotosaurus . The clade is well supported, with a jackknife value of 60, and Bremer support of 4. In the Bayesian topology, Dryosauridae also contains Valdosaurus as sister to the Kirkwood taxon (PP=0.27).