''Yixianosaurus'' (meaning "Yixian lizard") is a

maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...

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 ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 ...

of 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 specime ...

, ''Yixianosaurus longimanus'', was formally named and described by Xu Xing and

Wang Xiaolin Wang may refer to: Names * Wang (surname) (王), a common Chinese surname * Wāng (汪), a less common Chinese surname * Titles in Chinese nobility * A title in Korean nobility * A title in Mongolian nobility Places * Wang River in Thailand ...

in 2003. Its partial skeleton was discovered in 2001, in Liaoning at Wangjiagou in northeastern China. The generic name refers to the

Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its exq ...

. The specific name means "with a long hand" from

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 ...

''longus'', "long", and ''manus'', "hand".Xu, X. and Wang, X. (2003).
A new maniraptoran dinosaur from the Early Cretaceous Yixian Formation of western Liaoning
. ''Vertebrata PalAsiatica'', 41(3): 195–202.

Description

''Yixianosaurus'' is known only from a single specimen,

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 sever ...

IVPP V12638, which likely derived from the Dawangzhangzi Bed (early Aptian stage, 122 million years ago).Xu, X. and Norell, M.A. (2006). "Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China."''Geological Journal'', 41: 419–437. It is a

compression fossil A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way. The reason f ...

, viewed from behind and preserved on a single slab that has been sawed into several pieces. It consists of the

shoulder girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...

and a pair of fossilized arms complete with fossilized feathers, some ribs, 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 thes ...

. ''Yixianosaurus'' has a very long hand, 140% of the length of the 89 millimeter (3.5 in) humerus. The second finger is the longest. The fingers bear large and recurved claws. The feathers are not preserved well enough to show a specific structure, but they appear similar to the contour feathers of some Yixian Formation

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 lightweig ...

s. The large hands could have served in catching prey or assisted in climbing. The total body length has been estimated at 1 meter (3.3 ft), the weight at 1 kilogram (2.2 lbs). Xu et al. (2013) suggested that the presence of large pennaceous feathers on parts of the forelimb strongly supports that ''Yixianosaurus'' was adapted for limited aerial locomotion.Xu Xing, Corwin Sullivan & Wang Shuo (2013
The systematic position of the enigmatic theropod dinosaur Yixianosaurus longimanus
''Vertebrata PalAsiatica'' 51(3): 169-183

Classification

Yixianosaurus longimanus size comparison

The describers considered the exact placement of ''Yixianosaurus'' within

Maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...

to be uncertain, but because the hand length resembled that of another

feathered dinosaur A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form. It has been su ...

, '' Epidendrosaurus'' (now '' Scansoriopteryx''), they suggested it was a close relative of the

Scansoriopterygidae Scansoriopterygidae (meaning "climbing wings") is an extinct family of climbing and gliding maniraptoran dinosaurs. Scansoriopterygids are known from five well-preserved fossils, representing four species, unearthed in the Tiaojishan Formatio ...

. Other researchers have suggested the specimen may have come from a

dromaeosaurid 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 ...

. Subsequent analyses were divided on whether is it is more primitive and outside the clade

Eumaniraptora Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avial ...

– this would mean that advanced characteristics such as the long hands and short arms evolved independently in this species – or a basal member of the more advanced

Paraves Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avial ...

. In a 2017 re-evaluation of the Harlem '' Archaeopteryx'' specimen as an anchiornithid called '' Ostromia'', ''Yixianosaurus'' is found to be the most basal paravian. However, two other studies published the same year argued that ''Yixianosaurus'' was most closely related to ''

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 hol ...

'', with both genera being either relatives of scansoriopterygids or anchiornithids.

References

{{Taxonbar, from=Q2029031 Prehistoric maniraptorans Early Cretaceous dinosaurs of Asia Feathered dinosaurs Fossil taxa described in 2003 Taxa named by Xu Xing Yixian fauna Cretaceous birds