''Kompsornis'' (meaning "elegant bird") 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 ...

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 ...

that lived during the

Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

Cretaceous period The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of t ...

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 ...

. The type and only known

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

is ''Kompsornis longicaudus''; the specific name means "long-tailed". It is known from only 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 from 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 ...

. ''Kompsornis'' was closely related to the well-known ''

Jeholornis ''Jeholornis'' (meaning "Jehol bird") is a genus of avialans that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil ''Jeholornis'' were first discovered in the Jiufotang Formation in Heb ...

'', another long-tailed avialan from China, but differs from it in features of its skeleton, particularly the fusion and growth rate of its bones. Like other jeholornithiforms, ''Kompsornis'' was a long-tailed avialan with long

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...

s and possessed little or no teeth, with none identified in the single specimen of ''Kompsornis''.

Classification

''Kompsornis'' was described and named by Wang and colleagues in 2020 from the sole specimen AGB-6997, an articulated complete skeleton preserved on a single slab, and was recognised as a jeholornithiform avialan. Their description included a comprehensive comparison between ''Kompsornis'' and the

type specimen In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...

s of other named jeholornithiform species, including all species of ''Jeholornis'', ''

Shenzhouraptor sinensis ''Jeholornis'' (meaning "Jehol bird") is a genus of avialans that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil ''Jeholornis'' were first discovered in the Jiufotang Formation in Heb ...

'', '' Dalianraptor cuhe'' and the possible euavialan ''

Jixiangornis orientalis ''Jixiangornis'' is a genus of basal avialans from the Early Cretaceous. Like later avialans, it had no teeth, but it also had a long tail, unlike modern birds. Since teeth were still present in some more derived short-tailed avialans, ''Jixiang ...

''. They concluded that ''Kompsornis'' was a distinct species from all other jeholornithiform species, and that they all represented valid species except for ''Dalianraptor'', which was determined to be an artificial forgery of different specimens and lacking any diagnostic characteristics. A

phylogenetic analysis 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 ...

supported this conclusion, which recovered ''Kompsornis'' as a jeholornithiform most closely related to ''Jeholornis prima'' and ''J. curvipes'' (''Jeholornis'' 'sensu stricto'), and more derived than ''Shenzhouraptor'', ''J. palmapenis'' and ''Jixiangornis'': ''Kompsornis'' is distinguished from other jeholornithiform species by traits such as a more posteriorly directed pubis, especially elongated

caudal vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

in the tail, extreme tail length, longer forelimbs, and features of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

and

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 ...

in the shoulder. The

hip In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

and sternum are also more extensively fused than in other jeholornithiforms, despite its immaturity, and the skeleton overall has more bird-like growth patterns than in other sampled jeholornithiforms.

Palaeobiology

The growth rate of ''Kompsornis'' was sampled from a cross-section of a rib bone and compared to those of ''Jeholornis'' sp. The specimen was determined to be at least four years old and approaching maturity, but was not yet fully grown. ''Kompsornis'' possessed a different growth strategy to ''Jeholornis'', particularly in the fusion of the sternum and hips prior to skeletal maturity, which often remain unfused even in larger and older specimens of ''Jeholornis''. Such differences in growth patterns may be evidence that jeholornithiforms evolved distinct growth strategies to adopt different ecologies in the same environment. The sternum is completely fused, and possesses a well-developed

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

and a robust

xiphoid process The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Both ...

, suggesting that ''Kompsornis'' was a powerful flier.

References

Prehistoric avialans Early Cretaceous birds of Asia Bird genera Jiufotang fauna Fossil taxa described in 2020 {{paleo-bird-stub