''Chaoyangia'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of euornithean

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, 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 preserved ...

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 (Chinese: 九佛堂组, pinyin: ''jiǔfótáng zǔ'') is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see ...

near the city of Chaoyang in

Liaoning Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...

province,

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 ...

. This rock formation has been dated to the

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

age of the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

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 (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, 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 ...

(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 (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

). 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 ''Zhong ...

'', 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 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 cl ...

. Hou, who recognized the species as a euornithean, also placed it in its own order, 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 a prehistoric bird genus 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 Aptian, 125-120 milli ...

''. 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, People's Republic of China, China: ''Yanornis martini'', based on several fossils found in the 120-million-ye ...

'' as found by previous studies.

References

Early Cretaceous birds of Asia Fossil taxa described in 1993 Prehistoric euornitheans {{paleo-bird-stub