Article: Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae
Herrerasaurids were predatory, obligatorily bipedal dinosaurs recorded in early Late Triassic rocks of South America. It has been suggested recently that the Herrerasauridae constitute a paraphyletic assemblage, but several apomorphic traits in the dorsal, sacral, and caudal vertebrae and the pectoral and pelvic girdles support the monophyly of this group. The relationships of Dinosauria with other members of Ornithodira are considered, supporting the monophyly of the newly recognized clade Dinosauriformes, constituted of Lagosuchus + (Pseudolagosuchus+ (Dinosauria)). The Dinosauria, including Herrerasauridae, Saurischia, and Ornithischia, is diagnosed on the basis of six synapomorphic traits. The hypothesis that the Herrerasauridae constitute the sister-group of the remaining dinosaurs is supported here on the basis of four apomorphic traits uniquely shared by Saurischia and Ornithischia. The recently coined name Eudinosauria is used for the group of dinosaurs including the common ancestor of Saurischia, Ornithischia, and all of its descendants.