Effigia okeeffeae is named based on a well-preserved nearly complete skeleton from the Upper Triassic (?Rhaetian) “siltstone member” at Ghost Ranch, northern New Mexico. The skull is described and compared to other suchian and basal archosaurs. The maxilla and premaxilla are edentulous, and a rhamphotheca was possibly present in life.
Effigia conclusively indicates that the skull of Shuvosaurus and the postcrania of “Chatterjeea” belong to the same taxon. Furthermore, the close relationship between Shuvosaurus and Effigia indicates that both taxa are nested within the suchian clade and not within Ornithomimisauria. However, the similarity in features in the skull and postcrania of Effigia and ornithomimids suggests extreme convergence occurred between the two clades.
A clade containing Arizonasaurus, Bromsgroveia, Poposaurus, Sillosuchus, Shuvosaurus, and Effigia is suggested based solely on shared derived character states. Additionally, a clade (Clade Y) containing Sillosuchus, Shuvosaurus, and Effigia is well supported by further derived character states. The distribution and temporal pattern of members of Group Y suggest that members of Group Y are present in the early Middle Triassic through the Latest Triassic of North America, and one member of the clade, Sillosuchus, was present in South America.