''Xiyunykus'' (meaning "western claw"; "xiyu" is

Mandarin Mandarin or The Mandarin may refer to: Language * Mandarin Chinese, branch of Chinese originally spoken in northern parts of the country ** Standard Chinese or Modern Standard Mandarin, the official language of China ** Taiwanese Mandarin, Stand ...

for "west" and refers to Western China where it was found) is an alvarezsaur from the Early Cretaceous of the

Tugulu Group The Tugulu Group () is a geological Group in Xinjiang, China whose strata date back to the Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the ...

of China. It includes one species, ''Xiyunykus pengi''.

Paleoecology

Dinosaurs contemporaneous with ''Xiyunykus'' in the Tugulu Group of Xinjiang include the stegosaur ''

Wuerhosaurus ''Wuerhosaurus'' is a genus of stegosaurid dinosaur from the Early Cretaceous Period of western China and Inner Mongolia. As such, it was one of the last genera of stegosaurians known to have existed, since most others lived in the late Jurassic ...

'', the coeval alvarezsaur ''

Tugulusaurus ''Tugulusaurus'' (meaning "Tugulu lizard") is a genus of coelurosaurian theropod dinosaur that belongs to the Alvarezsauroidea. It is known from the Early Cretaceous Tugulu Group in the Urhe area of the People's Republic of China. It was one of ...

'', the carcharodontosaurid '' Kelmayisaurus'', the dubious maniraptoran ''

Phaedrolosaurus ''Phaedrolosaurus'' is a genus of theropod dinosaur, based on a single tooth possibly from the Valanginian-Albian-age Lower Cretaceous Lianmugin Formation of Wuerho, Xinjiang, People's Republic of China, China. Discovery and naming The first kn ...

'', the problematic coelurosaur ''

Xinjiangovenator ''Xinjiangovenator'' (meaning "Xinjiang hunter") is a genus of coelurosaurian dinosaur, dinosaurs, possibly part of the group Maniraptora, which lived during the Early Cretaceous Period (geology), period, sometime between the Valanginian and Albi ...

'', and the ceratopsian '' Psittacosaurus xinjiangensis''.

Evolutionary significance

''Xiyunykus'', along with ''

Bannykus ''Bannykus'' is an alvarezsaur from the Early Cretaceous of the Bayin-Gobi Formation of Inner Mongolia, China. It includes one species, ''Bannykus wulatensis''. It is large for an alvarezsaur, with an estimated weight of 24 kg based on fe ...

'', fills a 70-million year gap in alvarezsaur evolution by exhibiting cranial and postcranial morphologies intermediate between the typical theropod forelimb of ''

Haplocheirus ''Haplocheirus'' is a genus of theropod dinosaur. Upon its description, it was considered the oldest alvarezsauroid, predating all other members by about 63 million years. This has subsequently been questioned. A 2019 study considered ''Haploc ...

'' and the highly reduced forelimbs and minute teeth of Late Cretaceous alvarezsaurids.

References

Alvarezsaurs Fossil taxa described in 2018 Early Cretaceous dinosaurs of Asia {{theropod-stub