What is Averostra?

Ceratosaurus nasicornis, Allosaurus fragilis, their most recent common ancestor and all its descendants. Averostra marks a deep split within Neotheropoda, the point where Ceratosauria and Tetanurae unite while the coelophysoids and dilophosaurids continue to do their own thing. Averostrans share a set of features that reshape the skull and pelvis: the small teeth at the tip of the snout become uneven in size rather than simply cone-shaped, a tiny opening appears in the bone forming the front edge of the eye socket, the teeth in the upper jaw reduce in number, and the jaw itself loses the "kink" that characterises earlier neotheropods—producing the smoother "bird-snout" profile for which the group is named. The front of the uppermost pelvic bone expands, providing more attachment area for the muscles that powered their legs.

Once Averostra takes shape, it diversifies quickly. Ceratosaurs develop deep, ornamented skulls, reduced arms, and fused ankles that stiffen the legs. Tetanurans, by contrast, develop a stiff tail, enlarged hands, and front-loaded jaws, innovations that refine balance, prey handling, and running performance. Together, these two branches take over the predatory world, with ceratosaurs ruling the southern continents while tetanurans dominate the northern ones, and between them they fill every major carnivorous niche for the rest of the Mesozoic.

Click here to search Dinochecker for averostrans. Averostra is derived from the Latin "avis" (bird) and "rostra" (plural of "rostrum", meaning snout).