Ornithothoraces is a group of

avialan Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...

s that includes all enantiornithes ("opposite birds") and the

euornithes Euornithes (from Greek ' meaning "true birds") is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to '' Sinornis''. Description Clarke ''et al''. (2006) found that the most primitive kn ...

("true birds"), which includes modern

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

s and their closest ancestors. The name Ornithothoraces means "bird thoraxes". This refers to the modern, highly advanced anatomy of the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

that gave the ornithothoracines superior flight capability compared with more primitive avialans. This anatomy includes a large, keeled breastbone, elongated

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

s and a modified

glenoid The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sha ...

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 ''Protopteryx'' is an extinct bird and the most basal enantiornithean, from the Cretaceous period.Zhou, Zhonghe. (2002). "A new and primitive enantiornithine bird from the Early Cretaceous of China." ''Journal of Vertebrate Paleontology'', 22(1): ...

'', '' Eopengornis martini'', and '' Cruralispennia multidonta'', as well as the euornithine '' Archaeornithura meemannae'', all from the Sichakou Member of the

Huajiying Formation The Huajiying Formation is a geological formation in Hebei, People's Republic of China. Known for its fossils including feathered dinosaurs, the age of the formation is uncertain. It may represent an early portion of the Jehol Biota, dating to s ...

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'', 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.
/ref>

Classification

In 1994, Chiappe and Calvo established a

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

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'' and modern birds, and all of its other descendants. In 1998,

Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...

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