Ornithothoraces is a group of avialans that includes all

enantiornithes The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...

("opposite birds") and the euornithes ("true birds"), which includes modern birds and their closest ancestors. The name Ornithothoraces means "bird thoraxes". This refers to the modern, highly advanced anatomy of the thorax that gave the ornithothoracines superior flight capability compared with more primitive avialans. This anatomy includes a large, keeled breastbone, elongated coracoids and a modified glenoid joint in the shoulder, and a semi-rigid rib cage. In spite of this at least the sternum seems to have developed convergently rather than being a true homology. The earliest known members of the group are the enantiornitheans '' Protopteryx fengningensis'', '' Eopengornis martini'', and '' Cruralispennia multidonta'', as well as the euornithine '' Archaeornithura meemannae'', all from the Sichakou Member of the Huajiying Formation in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

, which has been dated to 130.7 million years old. At least one other enantiornithean, ''

Noguerornis gonzalezi ''Noguerornis'' is a genus of enantiornithine bird possibly related to ''Iberomesornis''. It lived during the Early Cretaceous (early Barremian age) about 130 mya and is known from fossils found in the La Pedrera de Rúbies Formation at El Mont ...

'', may be even older, at up to 145.5 million years ago, though its exact age is uncertain.Holtz, Thomas R. Jr. (2012) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2011 Appendix.
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Classification

In 1994, Chiappe and Calvo established a phylogenetic definition of the group. They defend Ornithothoraces as a node-based

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

, the common ancestor of ''

Iberomesornis romerali ''Iberomesornis'' ("Spanish intermediate bird") is a monotypic genus of enantiornithine bird of the Cretaceous of Spain. Discovery In 1985 the fossil of ''Iberomesornis'' was discovered by Armando Díaz Romeral in the Early Cretaceous Calizas ...

'' and modern birds, and all of its other descendants. In 1998, Paul Sereno defined Ornithothoraces in the same way, but used '' Sinornis santensis'' instead of ''Iberomesornis romerali''. The cladogram below follows the results of a phylogenetic analysis by Wang ''et al.'', 2016:

References

{{Taxonbar, from=Q135333 Avialans Taxa named by Jorge O. Calvo Taxa named by Luis M. Chiappe