Yanornis
Encyclopedia
Yanornis is an extinct genus of omnivorous Early Cretaceous
bird
s, thought to be closely related to the common ancestor of all modern birds. One species, Yanornis martini,
has been described from fossils found in the Jiufotang Formation
at Chaoyang, Western Liaoning province, PRC
, and as of 2004 five specimens were known. The age of the Jiufotang Formation is estimated to be early Aptian
, about 120 million years ago. The genus name Yanornis is derived from the Ancient Chinese Yan dynasties, whose capital was at Chaoyang, and Ancient Greek
ornis, "bird". The species Y. martini was named for avian paleontologist Larry Martin
.
It was the size of a chicken, had a long skull with about 10 teeth in the upper jaw and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula
(wishbone). It ate a varied diet and was capable of switching between major food sources, including fish and seeds, as evidenced by some specimens which preserve large amounts of gastrolith
s in the stomach. Its fish-eating and associated adaptations shows convergent evolution
to the unrelated enantiornithine
Longipteryx
.
The absence of the prefrontal bone
and the non-diapsid
skull place Yanornis into the Ornithurae
which also includes the common ancestor of living birds. Similarly, its scapula
and coracoid had evolved the basic shape and layout as in modern birds; enabling Yanornis to lift its wings far above its back for an efficient upstroke
. It thus was a more efficient flyer compared to Enantiornithes (which have the modern condition in a less well-developed form), let alone Confuciusornis
which like Archaeopteryx
was only marginally able to perform an upstroke. To allow for the necessarily large flight muscles, its sternum was longer than wide, again representing an essentially modern condition, as did many features of its arm skeleton.
to make the paleontological forgery "Archaeoraptor
". Upon discovering this, the bird half was described as Archaeovolans repatriatus, which was later found to be a junior synonym of Yanornis. See Archaeoraptor
. Some studies have also found that the bird species Aberratiodontus wui is in fact a poorly preserved specimen of Yanornis martini, or at least a close relative, an opinion which has been supported by subsequent reviews of enantiornithine taxonomy.
In a 2006 study of early bird relationships, it was found that Yanornis, Yixianornis
, and Songlingornis
formed a monophyletic group; since Songlingornis was the first of these birds to be described, the family containing this group is Songlingornithidae
. The order Yanornithiformes has been erected to mark their distinctness from other early Ornithurae such as Gansus
, but might be called Songlingornithiformes; especially if the present taxon is indeed a junior synonym of Songlingornis as sometimes proposed.
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, thought to be closely related to the common ancestor of all modern birds. One species, Yanornis martini,
has been described from fossils found in the Jiufotang Formation
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. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
at Chaoyang, Western Liaoning province, PRC
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
, and as of 2004 five specimens were known. The age of the Jiufotang Formation is estimated to be early Aptian
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 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
, about 120 million years ago. The genus name Yanornis is derived from the Ancient Chinese Yan dynasties, whose capital was at Chaoyang, and Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
ornis, "bird". The species Y. martini was named for avian paleontologist Larry Martin
Larry Martin
Larry Martin is an American vertebrate paleontologist and curator of the Natural History Museum and Biodiversity Research Center at the University of Kansas. Among Martin's work is research on the Triassic reptile Longisquama and theropod dinosaur Caudipteryx...
.
It was the size of a chicken, had a long skull with about 10 teeth in the upper jaw and 20 teeth in the lower jaw, and was both able to fly and walk well, having a well-developed U-shaped furcula
Furcula
The ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
(wishbone). It ate a varied diet and was capable of switching between major food sources, including fish and seeds, as evidenced by some specimens which preserve large amounts of gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...
s in the stomach. Its fish-eating and associated adaptations shows convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
to the unrelated enantiornithine
Enantiornithes
Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over 50 species of Enantiornithines have been named, but some...
Longipteryx
Longipteryx
Longipteryx is a genus of prehistoric bird which lived during the Early Cretaceous . It contains a single species, Longipteryx chaoyangensis. Its remains have been recovered from the Jiufotang Formation at Chaoyang in Liaoning Province, People's Republic of China...
.
The absence of the prefrontal bone
Prefrontal bone
The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and extinct lungfish, amphibians and reptiles...
and the non-diapsid
Diapsid
Diapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
skull place Yanornis into the Ornithurae
Ornithurae
Ornithurae is the name of a natural group which includes all modern birds as well as their extinct relatives with plough-shaped pygostyles, a bone at the end of the tail which allows the tail feathers to fan and retract....
which also includes the common ancestor of living birds. Similarly, its scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
and coracoid had evolved the basic shape and layout as in modern birds; enabling Yanornis to lift its wings far above its back for an efficient upstroke
Bird flight
Flight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
. It thus was a more efficient flyer compared to Enantiornithes (which have the modern condition in a less well-developed form), let alone Confuciusornis
Confuciusornis
Confuciusornis is a genus of primitive crow-sized birds from the Early Cretaceous Yixian and Jiufotang Formations of China, dating from 125 to 120 million years ago...
which like Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
was only marginally able to perform an upstroke. To allow for the necessarily large flight muscles, its sternum was longer than wide, again representing an essentially modern condition, as did many features of its arm skeleton.
Taxonomy and systematics
Yanornis gained notoriety when the front half of a fossil bird was combined with the tail of a MicroraptorMicroraptor
Microraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China...
to make the paleontological forgery "Archaeoraptor
Archaeoraptor
"Archaeoraptor" is the generic name informally assigned in 1999 to a fossil from China in an article published in National Geographic magazine. The magazine claimed that the fossil was a "missing link" between birds and terrestrial theropod dinosaurs. Even prior to this publication there had been...
". Upon discovering this, the bird half was described as Archaeovolans repatriatus, which was later found to be a junior synonym of Yanornis. See Archaeoraptor
Archaeoraptor
"Archaeoraptor" is the generic name informally assigned in 1999 to a fossil from China in an article published in National Geographic magazine. The magazine claimed that the fossil was a "missing link" between birds and terrestrial theropod dinosaurs. Even prior to this publication there had been...
. Some studies have also found that the bird species Aberratiodontus wui is in fact a poorly preserved specimen of Yanornis martini, or at least a close relative, an opinion which has been supported by subsequent reviews of enantiornithine taxonomy.
In a 2006 study of early bird relationships, it was found that Yanornis, Yixianornis
Yixianornis
Yixianornis is a bird genus from the early Cretaceous period. Its remains have been found in the Jiufotang Formation at Chaoyang dated to the early Aptian age, around 120 million years ago. Only one species, Yixianornis grabaui, is known at present...
, and Songlingornis
Songlingornis
Songlingornis is a prehistoric bird genus from the Early Cretaceous. Its fossils have been found in the Jiufotang Formation of Liaoning . The age of these rocks is somewhat disputed, but probably around the early Aptian, 125-120 million years ago...
formed a monophyletic group; since Songlingornis was the first of these birds to be described, the family containing this group is Songlingornithidae
Songlingornithidae
Songlingornithidae is a family of early ornithurine birds from the early Cretaceous Period of China. All known specimens come from the Jiufotang Formation, dating to the early Aptian age, 120 million years ago....
. The order Yanornithiformes has been erected to mark their distinctness from other early Ornithurae such as Gansus
Gansus
Gansus is a genus of aquatic birds that lived during the Aptian or Albian age of the Early Cretaceous period in what is now Gansu province, western China...
, but might be called Songlingornithiformes; especially if the present taxon is indeed a junior synonym of Songlingornis as sometimes proposed.