Ornithothoraces

Ornithothoraces is a clade of birds which includes all enantiornithines and modern birds (Neornithes).

The name Ornithothoraces means "bird thoraxes". This refers to a modern, highly derived, anatomy of the thorax which gave the ornithothoracines superior flight capability compared to more primitive birds. This anatomy includes elongated coracoids, a large, keeled sternum, and modified glenoid joint of the shoulder, along with a semirigid dorsal rib cage. The earliest known member of the group is Protopteryx fengningensis, from the Sichakou Member of the Huajiying Formation of China, which dates to around 131 Ma ago, though at least one other enantiornithine, Noguerornis, may be even older, at up to 145.5 million years ago, though its exact age is uncertain.

Definition
Under older classifications, the primitive toothed members of the group was united in the superorder Odontognathae, which together with the Palaeognathae and Neognathae comprised the Neornithes. In 1994, Chiappe and Calvo forwarded a phylogenetic definition of Ornithothoraces as the common ancestor of Iberomesornis romerali and extant birds, plus all their descendants. This was followed by Chiappe in 1996. This definition gives a node-based clade.

Sereno (1998) defined Ornithothoraces in the same node-based way, but used Sinornis santensis instead of Iberomesornis.