Dinosauriformes

Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs, and an at least partially perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.

The term Dinosauriformes was coined and defined in 1992 by F.E. Novas, who used it to include the herrerasaurs, which he did not consider members of Dinosauria proper. Contrary to Novas, most paleontologists since 1992 have considered herrerasaurs to be true dinosaurs, though many other primitive, dinosaur-like reptiles fall within his definition of Dinosauriformes. Dinosauriformes fall within the clade Dinosauromorpha.

Phylogeny
Cladogram simplified after Nesbitt (2011):