''Chaoyangia'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

euornithean 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 the enantiornithines. This group was defined in the ''PhyloCode'' by Juan Benito and ...

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s, containing the single species ''Chaoyangia beishanensis''. This species is known from a single

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

specimen consisting of a partial skeleton including vertebra, ribs, hips, and upper legs. The specimen (museum catalog number IVPP V9934) was discovered in the

Jiufotang Formation The Jiufotang Formation () is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. T ...

near the city of Chaoyang in

Liaoning ) , image_skyline = , image_alt = , image_caption = Clockwise: Mukden Palace in Shenyang, Xinghai Square in Dalian, Dalian coast, Yalu River at Dandong , image_map = Liaoning in China (+all claims hatched).svg , ...

province,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. This rock formation has been dated to the

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

age of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

period, 120 million years ago.

Description

''C. beishanensis'', known only from a single partial skeleton, is relatively poorly known compared to other primitive euornitheans. ''Chaoyangia'' were small, basal euornithean birds characterized by more than eight fused

sacral vertebrae The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

(those connected to the hips), uniquely long, slender, and angled uncinate processes on the ribs, and a distinct 'neck' in the upper leg bone (

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

). Overall, the known skeleton is very similar to another primitive Chinese euornithean bird, ''

Zhongjianornis ''Zhongjianornis'' is a genus of beaked, pigeon-sized birds from the early Cretaceous period of China. It is known from one fossil found at Jianchang, Liaoning Province, in rocks of the Jiufotang Formation, representing the type species ''Zhongji ...

'', which is known from a much more complete skeleton.

History and classification

''C. beishanensis'' was among the first fossil bird species found in the

Jehol biota The Jehol Biota includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. These d ...

of China. At the time of its discovery, it was seen as being quite distinct from all other known birds at the time.O'Connor, J.K. and Zhou Z. (2012). "A redescription of ''Chaoyangia beishanensis'' (Aves) and a comprehensive phylogeny of Mesozoic birds." ''Journal of Systematic Palaeontology'', (advance online publication). When additional specimens were found and referred to the species in 1997, it was regarded as a member of the Ornithurae (=Euornithes), the lineage including modern birds but not enantiornitheans. Hou, who recognized the species as a euornithean, also placed it in its own

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

, Chaoyangiformes.Hou L. (1997). ''Mesozoic birds of China.'' Taiwan Provincial Feng Huang Ku Bird Park, Taiwan. The additional fossil specimens referred to ''Chaoyangia'', one a partial skeleton including partial wing bones and a partial skull, and the other an isolated foot, did not contain any bones in common with the original specimen, and so it was impossible to determine whether or not they actually belonged to the same genus. The more complete specimen including the partial skull was later classified in its own genus, ''

Songlingornis ''Songlingornis'' is an extinct genus of ornithuromorph dinosaurs from the Early Cretaceous. Its fossils have been found in the Jiufotang Formation of Liaoning (PRC). The age of these rocks is somewhat disputed, but probably around the early Apt ...

''. The removal of this specimen from ''Chaoyangia'' left its identity uncertain, and some researchers continued to suspect ''Songlingornis'' and ''Chaoyangia'' were synonyms. In 2012, paleontologists Jingmai O'Connor and Zhou Zhong re-described the original ''Chaoyangia'' specimen, and confirmed that it was indeed a primitive euornithean (=ornithuran) using a phylogenetic analysis. Their study also supported the distinction between ''Chaoyangia'' and ''Songlingornis'', with the latter bird more closely related to ''

Yanornis ''Yanornis'' () is an extinct genus of fish-eating Early Cretaceous birds. Two species have been described, both from Liaoning province, China: ''Yanornis martini'', based on several fossils found in the 120-million-year-old Jiufotang Formation ...

'' as found by previous studies.

References

{{Taxonbar, from=Q2042187 Euornithes Early Cretaceous dinosaurs of Asia Fossil taxa described in 1993