Dinosaur Classification

Figure 14: This cladogram shows the relationship between the theropod dinosaurs (notice the close relationship between Velociraptor of Maniraptora and Aves of Avialae).

Dinosaurs were divided into two groups Saurischia ("lizard hips") and Ornithischia ("bird hips") which distinguish them on the basis of their pelvic structure. In the pelvis of saurischian dinosaurs, the three pelvic bones radiate in different directions from the hip socket (acetabulum).

Saurischia consists of two clades, Theropoda and Sauropodomorpha. Primitive theropods, the ceratosaurs is a clade that split early from the theropod lineage and later branched into the carnosaurs and the coelurosaurs. The coelurosaurs were smaller, long-necked theropods having large forelimbs. Velociraptor belonged to the clade of coelurosaurs.

Figure 15: the phylogeny of theropods currently accepted by most palaeontologists identifies ceratosaurs as an early side branch from the main line of tetanuran evolution, which split into carnosaurs and coelurosaurs.