''Xixianykus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of alvarezsaurid theropod

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

from the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period of

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. Known from a slab of rock which contains a partial postcranial skeleton unearthed in the Late Cretaceous ( Coniacian-

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

) Majiacun Formation of the Xixia Basin in Henan, China.

Discovery and naming

The fossil,

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

XMDFEC V0011, was found in the Majiacun Formation in

Henan Henan; alternatively Honan is a province in Central China. Henan is home to many heritage sites, including Yinxu, the ruins of the final capital of the Shang dynasty () and the Shaolin Temple. Four of the historical capitals of China, Lu ...

Province,

. The fossil consists of a partial skeleton, without the skull. Parts of the hind legs, pelvis and spine has also been recovered. ''Xixianykus'' is among the oldest of the derived alvarezsauroids, the parvicursorines, dated to the

– Coniacian, as opposed to other parvicursorines, which are either

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

.Hone, D. (2010)
''Xixianykus zhangi'' - A New Alvarezsaur
Dave Hone's Archosaur Musings, April 23, 2011. The type species is ''Xixianykus zhangi'' described in 2010 by Xu Xing. The genus name refers to Xixia County and to the Greek word for claw ("''onyx''"). The latter is a common element used in names for Alvarezsaurids. The species name is in honor of Zhang Xinglao.

Description

''Xixianykus'' was a small animal, about long and high, and may have weighed just about 0.74 kg. It is one of the smallest-known dinosaurs (not counting avians). It appears to have many adaptations towards a cursorial (running) lifestyle. It was about 50 centimetres long but had legs and a short

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

combined with a long

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

and metatarsus, as well as including an arctometatarsalian pes, a highly modified structure in the feet of theropod dinosaurs used to enhance cursorial capability, which was found within the known fossil material, and these are all good indicators of it being a fast runner. It was probably covered in

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and an exa ...

s and had small, robust arms with one large claw for each hand, as well as a tubular snout used to feed likely on colonial insects. Despite claims by

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

that the remains assigned to ''Xixianykus'' belong to a juvenile individual, osteohistological analyses show that the remains assigned to ''Xixianykus'' belong to an adult individual.

References

External links

Agile 'roadrunner' dinosaur fossil discovered in China
{{Taxonbar, from=Q1920526 Alvarezsauroidea Dinosaur genera Campanian dinosaurs Dinosaurs of China Fossil taxa described in 2010 Taxa named by Xu Xing