''Yandangornis'' is a

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 ...

theropods 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 ca ...

(possibly

avialans 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 use ...

) from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

. It lived 81.5

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

in what is now China. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''Y. longicaudus'', was formally described by Cai and Zhou in 1999. 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 ...

specimen is a mostly complete skeleton in the collection of the

Zhejiang Museum of Natural History The Zhejiang Museum of Natural History is a museum that mainly focuses on exhibitions, collections and analysis on specimens of life science and earth science. The museum is one of the earliest museums of natural history created by Chinese peopl ...

, with accession number M1326. The fossil was discovered in 1986, near Linhai City in Zhejiang Province, China. It includes most of one complete skeleton. The genus was named after the

Yandang mountains Yandang Mountains or Yandangshan (Chinese language, Chinese: traditional characters, t , simplified characters, s , pinyin, p ''Yàndàng Shān'', lit. "Wild Goose Pond Mountain(s)") refers, in the broad sense, to a coasta ...

Description

The specimen is small, roughly the size of ''

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" ...

'', with a total length around , of which 30.5 centimeters (1 foot) is tail. It is preserved in a seated position and visible from the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

aspect. After ''Archaeopteryx'', ''Yandangornis'' was the second genus of primitive bird found preserving a long, bony tail, and this trait was responsible for the specific name ''longicaudus,'' which is

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 ...

for "long tail". The skull is flattened, about long. It is lightly built and toothless, with a short mouth and robust

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

e presumably possessing a horny

beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food ...

. These characteristics are similar to those of ''

Confuciusornis ''Confuciusornis'' is a genus of basal crow-sized avialan from the Early Cretaceous Period of the Yixian and Jiufotang Formations of China, dating from 125 to 120 million years ago. Like modern birds, ''Confuciusornis'' had a toothless beak, b ...

''. The forelimbs, though incomplete, are generally similar to those of ''Archaeopteryx''. 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 ...

is large and unkeeled, but possesses an expanded middle posterior portion and

gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...

. The hind limbs are long and robust, particularly the

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 ...

and

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These sm ...

. The

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

and

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 ...

, on the other hand, are short. The small first toe is at a higher level than the other three toes and does not possess a reversed hallux. The toes were long and slender, with short, blunt claws. Unlike in several other avialans and paravians, the second toe did not have a large, curved claw. ''Yandangornis'' had some features that suggest a terrestrial mode of life, such as blunt toe claws, a non-reversed hallux of the first toe, and strong legs. This lifestyle may have evolved in response to the long, heavy tail of the genus, which would have inhibited flying ability.Cai, Z. & Zhao, L. (1999). "A long tailed bird from the Late Cretaceous of Zhejiang". ''Science in China Series D-Earth Sciences'' Vol. 42, No. 4, 1999 pp.434-441.

Classification

Cai and Zhao placed ''Yandangornis'' in a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

(Yandangithidae) and order (Yandangithiformes) in the subclass

Sauriurae Sauriurae (meaning "lizard tails" in Greek) is a now-deprecated subclass of birds created by Ernst Haeckel in 1866. It was intended to include '' Archaeopteryx'' and distinguish it from all other birds then known, which he grouped in the sister-g ...

of the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Aves 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 ...

. In fact, they considered that it was a direct descendant of ''Archaeoptyerx'', albeit as part of a lineage of long-tailed terrestrial birds distinct from modern birds. However, Sauriurae (long-tailed birds) has generally been discredited as an invalid

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

group.Gauthier, Jacques, de Queiroz, Kevin. (2001) "Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name 'Aves'". in "New Perspective on the Origin and Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom" Yale Peabody Museum. Yale University. New Haven, Conn. USA Aves, on the other hand, is currently restricted to the last common ancestor of all living birds and its descendants. As ''Yandangornis'' was far more primitive than members of Aves, it is not considered a member of that class using recent definitions. The usage of Aves within the description of ''Yandangornis'' more closely resembles the current clade

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 use ...

, which is defined as all animals more closely related to modern birds (Aves) than to

Troodontids 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 ...

and

Dromaeosaurids Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

. Other long-tailed avialans include ''

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 ...

'' and ''Archaeopteryx''. Zhou and Zhang, 2007, briefly noted that ''Yandangornis's'' affinities were not sufficiently diagnosed, and that ''Yandangornis'' may potentially be a non-avialan genus of theropod.Zhou, Zhonghe, Zhang, Fucheng. (2007) "Mesozoic birds of China––a synoptic review." "Frontiers of Biology in China" 2(1):1-14 ''Yandangornis'' is poorly documented in literature, and discussion of the genus has generally been omitted from recent reevaluations of avialan

systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic tre ...

References

External links

''Yandangornis'' on the Dinosaur Mailing List
{{Taxonbar, from=Q2492156 Prehistoric avialans Late Cretaceous birds of Asia Bird genera Fossil taxa described in 1999