Aurornis
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''Aurornis'' 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 anchiornithid
theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s from the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
period of
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 genus ''Aurornis'' contains a single 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 ...
, ''Aurornis xui'' (). ''Aurornis xui'' may be the most basal ("primitive")
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 ...
dinosaur known to date, and it is one of the earliest avialans found to date. The fossil evidence for the animal pre-dates that of ''
Archaeopteryx lithographica ''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" ...
'', often considered the earliest bird species, by about 10 million years. ''Aurornis xui'' was first described and named by Pascal Godefroit, Andrea Cau, Hu Dong-Yu, François Escuillié, Wu Wenhao and Gareth Dyke in
2013 File:2013 Events Collage V2.png, From left, clockwise: Edward Snowden becomes internationally famous for leaking classified NSA wiretapping information; Typhoon Haiyan kills over 6,000 in the Philippines and Southeast Asia; The Dhaka garment fact ...
. The generic name is derived from the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
word ''aurora'', meaning "daybreak" or "dawn", and the
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
ὄρνις (''órnis'') meaning "bird". The specific name, ''A. xui'', honors Xu Xing. A recent study of specimens of the avialan ''
Anchiornis ''Anchiornis'' is a genus of small, four-winged Paraves, paravian dinosaurs, with only one known species, the type species ''Anchiornis huxleyi'', named for its similarity to modern birds. The Latin name ''Anchiornis'' derives from a Greek word m ...
'' has found that the traits exhibited by ''Aurornis'' fall within the range of variation in ''Anchiornis'', warranting their synonymization.


Description

''Aurornis'' was roughly the size of a modern
pheasant Pheasants ( ) are birds of several genera within the family (biology), family Phasianidae in the order (biology), order Galliformes. Although they can be found all over the world in introduced (and captive) populations, the pheasant genera na ...
, with a length of . It had clawed wings and a long bony tail. Its leg bones were similar to those of ''Archaeopteryx'', but overall its anatomy was more primitive. ''Aurornis'' lived roughly 160 million years ago, roughly 10 million years before ''Archaeopteryx'', which often has been described as the first bird.


Discovery

''Aurornis'' was described from a
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
fossil in 2013. The fossil was purchased from a local dealer who said it had been unearthed in Yaoluguo in western
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 ...
, China. Subsequent analysis confirmed it came from the
Tiaojishan Formation The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian- Oxfordian stages). It is known for its exceptionally preserved fossils, including those of ...
, which has been dated to the late
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
period ( Oxfordian stage), approximately 160 million years ago. The fossil features traces of downy feathers along the animal's tail, chest, and neck. It was only partially prepared at the time of purchase with the feathers not showing, and bore no signs of forgery. On 7 June 2013, Science Magazine published an article that noted that
Pascal Godefroit Pascal Godefroit is a Belgian paleontologist. He discovered dinosaurs like '' Olorotitan'' in 2003. Godefroit is the director of earth and life sciences This list of life sciences comprises the branches of science that involve the scientific st ...
, the paleontologist who led the team that described ''Aurornis'', reported that he is uncertain if the fossil material came from Liaoning province's 160-million-year-old Tiaojishan Formation, as the information provided by the fossil dealer indicated, or from the province's 125-million-year-old Yixian Formation, which is known to have produced several ancient bird fossils. The failure to secure rigorous provenance information casts doubt on the claim that ''Aurornis'' is 160 million years old and predates ''
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" ...
''. Godefroit's team will attempt to confirm the specimen's provenance, and its age, by conducting mineralogical and botanical analysis on the shale slab and then publishing their findings. A 2017 study suggested that ''Aurornis'' may be a
junior synonym The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...
of ''Anchiornis''.


Classification

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 ...
analysis of ''Aurornis'' published in 2013 found that it belongs in the bird lineage, in a more basal position than ''
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" ...
''. The analysis was based on "almost 1,500 natomicalcharacteristics." On the other hand, a phylogenetic analysis conducted by Brusatte ''et al.'' (2014) recovered ''Aurornis'' outside Avialae; it was recovered as a
troodontid Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...
closely related to ''
Anchiornis ''Anchiornis'' is a genus of small, four-winged Paraves, paravian dinosaurs, with only one known species, the type species ''Anchiornis huxleyi'', named for its similarity to modern birds. The Latin name ''Anchiornis'' derives from a Greek word m ...
'', ''
Xiaotingia ''Xiaotingia'' is a genus of anchiornithid theropod dinosaur from Middle Jurassic or early Late Jurassic deposits of western Liaoning, China, containing a single species, ''Xiaotingia zhengi''. Discovery ''Xiaotingia'' is known from the holoty ...
'' and ''
Eosinopteryx ''Eosinopteryx'' is an extinct genus of theropod dinosaurs known to the late Jurassic period of China. It contains a single species, ''Eosinopteryx brevipenna''. Discovery and naming ''E. brevipenna'' is known from a single fossil specimen recov ...
''. In 2017 re-evaluation of the Harlem ''
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" ...
'' specimen, ''Aurornis'' is found to be an anchiornithid. The classification of ''A. xui'' as a bird is somewhat contentious, however, due to the various differing definitions of the word "bird". Recent discoveries " mphasizehow grey the dividing line is between birds and on-aviandinosaurs", says Paul Barrett of the
Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...
in
London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
. "There's such a gradation in features between them that it's very difficult to tell them apart ... 'Aurornis xui''is certainly an older member of the bird lineage than ''Archaeopteryx'', and it's fair to call it a very primitive bird. But what you call a bird comes down to what you call a bird, and a lot of definitions depend on ''Archaeopteryx''." Bird evolution specialist
Lawrence Witmer Lawrence M. Witmer (born October 10, 1959, at Rochester, New York) is an American paleontologist and paleobiologist. He is a Professor of Anatomy and a Chang Ying-Chien Professor of Paleontology at the Department of Biomedical Sciences at the Her ...
called the new analysis compelling, but said it remains difficult to distinguish birds from birdlike dinosaurs: "All of these little feathered species running and flapping around ... were all very similar." American paleontologist Luis Chiappe said that ''A. xuis forelimb is too short for this species to be a true bird. It "is very birdlike, but it is not yet a bird," he concluded. In his 2002 book ''Dinosaurs of the Air'',
Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...
tried to conceptually model a " pro-avian". In his view, the direct ancestors of birds cannot have been completely arboreal, because in that case they would probably have used membranes to fly. He thought they must have represented an intermediate ecological stage, in which the hindlimbs still had largely cursorial adaptations whereas the arms had been elongated in order to climb. Feathers, originally serving the insulation of an already warm-blooded animal, would by elongation have turned the arms into wings in order to fly. More generally, the proavians would, in view of their basal theropod forebears and bird descendants, have been typified by long necks, a short trunk, long fingers with opposable digits, a decoupling of the locomotor functions of the forelimbs and hindlimbs, a lack of a
propatagium The patagium (plural: patagia) is a membranous body part that assists an animal in obtaining lift when gliding or flight. The structure is found in extant and extinct groups of flying and gliding animals including bats, birds, some dromaeosaurs ...
, a shallow tail, and a weight of about one kilogramme. Paul illustrated his analysis with a skeletal diagram, accompanied by a life illustration of a "
proavis Proavis refers to a hypothetical extinct species or hypothetical extinct taxon and was coined in the early 20th century in an attempt to support and explain the hypothetical evolutionary steps and anatomical adaptations leading from non-avian ther ...
". When ''Aurornis'' was described in 2013, it was at the time the most basal known member of the
Avialae 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 ...
, the group consisting of birds and their closest relatives. The Italian paleontologist
Andrea Cau Andrea Cau is an Italian vertebrate paleontologist. He specializes in the study of dinosaur cladistics. Cau named the unique dromaeosaurid theropod, ''Halszkaraptor'' in 2017. He also reanalyzed the theropod ''Balaur'', placing it as a basal aviala ...
remarked it bore an uncanny resemblance to Paul's "proavis".


References


External links


A photograph of the type specimen, published by David Bressnan's twitter account

A closer view of the front part of the skeleton, published by Darren Naish's twitter account

A closer view of the tail and feathers, from the same source

A closer view of the skull and feathers, from the same source
{{Taxonbar, from=Q13407566 Jurassic birds Fossil taxa described in 2013 Late Jurassic dinosaurs of Asia Prehistoric paravians Transitional fossils Taxa named by Pascal Godefroit Paleontology in Liaoning Feathered dinosaurs