''Archaeornithura'' is an extinct

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 ...

ornithuromorph 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 know ...

s from the early

Cretaceous 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 th ...

period. It is known from two

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 ...

specimens of a single

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 ...

, ''Archaeornithura meemannae''. The specimens have been dated to the

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by the Va ...

age, 130.7 million years ago, making ''A. meemannae'' the oldest known ornithuromorph, the lineage that gave rise to 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 contains all living birds as well as many of their extinct relatives.

Discovery and naming

Both specimens of ''A. meemannae'', the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

STM7-145 and the

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). Of ...

STM7-163, were discovered in the interbedded

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

rocks 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 som ...

Hebei Province Hebei or , (; alternately Hopeh) is a northern province of China. Hebei is China's sixth most populous province, with over 75 million people. Shijiazhuang is the capital city. The province is 96% Han Chinese, 3% Manchu, 0.8% Hui, an ...

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 ...

. They were named and described by an international team of

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

s led by Wang and Zhou Zhonge of the

Institute of Vertebrate Paleontology and Paleoanthropology The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...

Beijing } Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...

. ''Archaeornithura'' is the first ornithuromorph found in the Huajiying Formation, which represents the earliest diversification period of 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 ...

, "the most important and diverse fossil avifauna known to science". Previously, the only birds known from the Huajiying Formation were

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 ...

. The genus name means "ancient ornithuromorph"; the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

was chosen in honor of Chinese paleontologist

Meemann Chang Meemann Chang (; born 17 April 1936) also known as Zhang Miman, is a Chinese paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP). She completed her undergraduate studies at Moscow University and completed her ...

. The discovery was announced in ''

Nature Communications ''Nature Communications'' is a peer-reviewed, open access, scientific journal published by Nature Portfolio since 2010. It is a multidisciplinary journal and it covers the natural sciences, including physics, chemistry, earth sciences, medicine, ...

'' in May 2015. Paleontologist

Stephen Brusatte Stephen Louis Brusatte (born April 24, 1984) is an American paleontologist and evolutionary biologist, who specializes in the anatomy and evolution of dinosaurs. He was educated at the University of Chicago for his BS degree, at the University of ...

, who was not affiliated with the study, called the discovery of ''A. meemannae'' "one of the most important ird fossilsfound over the last decade".

Description

''Archaeornithura'' had a moderately advanced plumage, fan-shaped tail feathers, a U-shaped

furcula The (Latin for "little fork") or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is formed by the fusion of the two pink clavicles. In birds, its primary function is in the strengthening of the thoracic ...

, highly fused wing apexes, and a well-developed

alula The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive of ''ala'', meaning "wing". The al ...

– a feathered first finger projecting on the front edge of the wing that is typically used to boost manoeuvrability during flight. Collectively, these traits mean that it shares many morphological features with a modern bird – more than found in any other bird of equivalent age. This suggests that the

Ornithuromorpha 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 know ...

diverged from other bird-related dinosaurs earlier than previously thought. "The new bird is quite

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

and has many advanced features of modern birds," said discoverer Wang Min. Before its discovery, the oldest known ornithuromorphs had been species living about 125 million years ago. It also suggests that key evolutionary advantages of birds – skilled flight and rapid growth in development – arose rapidly, and that

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

specialization happened early in bird history. The species had long legs and feet similar to modern

plovers Plovers ( , ) are a widely distributed group of wading birds belonging to the subfamily Charadriinae. Description There are about 66 species in the subfamily, most of them called "plover" or "dotterel". The closely related lapwing subfa ...

, suggesting that it was a shore bird that waded into shallow water to feed. The species appears to have been adept at flying. Both known specimens of ''A. meemannae'' are excellently preserved, including substantial feathers. Some ''Archaeornithura'' feathers feature a central groove, a trait thought to arise from derived flight feathers. This feature was not previously known in the Ornithuromorpha, suggesting that modern feather morphology, in which it is lacking, evolved separately from the ''

Archaeopteryx ''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...

'' lineage in a later subset of the ornithuromorphs. ''Archaeornithura'' is distinguished from its closest relatives by a combination of the following traits, each in itself not a unique

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

. The front edge of the sternum is strongly vaulted. The

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 ...

at the rear of the sternum is well-developed and has a rectangular outline. The first finger projects further than the second

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...

. The second phalanx of the second finger is longer than the first phalanx. The thighbone is short relative to the

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) and meta ...

Classification

''Archaeornithura'' was placed in the

Hongshanornithidae Hongshanornithidae is an extinct group of early ornithuromorph birds from the early Cretaceous period of China. It includes the genera '' Hongshanornis'' (the type genus) and '' Tianyuornis'' from the Yixian Formation of Inner Mongolia, ''Longic ...

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 ...

showed that ''Archaeornithura'' is closely related to more recent and derived hongshanornithids, and confirmed that the species earlier thought to have been hongshanornithids indeed together form a separate

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, ...

. ''Archaeornithura'' was shown to be the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

of '' Tianyuornis'', with partially fused

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...

II–IV and the expanded shape of the outermost

trabecula A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod that supports or anchors a framework of parts within a body or organ. A trabecula generally has ...

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 ...

in common. The specialized wading features of ''Archaeornithura'' suggest that the hongshanornithids originated in a semi-aquatic environment. The position of ''Archaeornithura'' in the

evolutionary tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

is shown by the following

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

References

{{Taxonbar, from=Q19859354 Bird genera Early Cretaceous birds of Asia Fossil taxa described in 2015 Fossils of China Hongshanornithids