''Yinlong'' (, meaning "hidden dragon") is a

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 ...

of basal ceratopsian

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 ...

from the Late

Jurassic Period The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

central Asia Central Asia, also known as Middle Asia, is a subregion, region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes t ...

. It was a small, primarily

biped Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

al herbivore.

Discovery and species

A coalition of American and

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

s, including Xu Xing,

Catherine Forster Catherine Ann Forster is an American paleontologist, taxonomist and expert in ornithopod evolution and ''Triceratops ''Triceratops'' ( ; ) is a genus of herbivorous chasmosaurine ceratopsid dinosaur that first appeared during the late ...

, Jim Clark, and Mo Jinyou, described and named ''Yinlong'' in 2006. The generic name is derived from the

Mandarin Chinese Mandarin (; ) is a group of Chinese (Sinitic) dialects that are natively spoken across most of northern and southwestern China. The group includes the Beijing dialect, the basis of the phonology of Standard Chinese, the official language ...

words 隱 (''yǐn'': "hidden") and 龍 (''lóng'': "dragon"), a reference to the movie '' Crouching Tiger, Hidden Dragon'', large portions of which were filmed in the western Chinese province of

Xinjiang Xinjiang, SASM/GNC: ''Xinjang''; zh, c=, p=Xīnjiāng; formerly romanized as Sinkiang (, ), officially the Xinjiang Uygur Autonomous Region (XUAR), is an autonomous region of the People's Republic of China (PRC), located in the northwest ...

, near the locality where this animal's

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains were discovered. ''Long'' is the word most often used in the Chinese media when referring to dinosaurs. The

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

was named after the American vertebrate paleontologist William Randall Downs III, a frequent participant in paleontological expeditions to China who died the year before ''Yinlong'' was discovered.Xu, X., Forster, C.A., Clark, J.M., and Mo, J. (2006).
A basal ceratopsian with transitional features from the Late Jurassic of northwestern China
" ''Proceedings of the Royal Society B: Biological Sciences'', 273(1598): 2135-2140. The known fossil material of ''Yinlong'' consists of many skeletons and skulls. The first specimen discovered was a single exceptionally well-preserved skeleton, complete with

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

, of a nearly adult animal, found in 2004 in the Middle-

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

strata of the

Shishugou Formation The Shishugou Formation () is a geological formation in Xinjiang, China. Its strata date back to the Late Jurassic period. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (2004). "Din ...

located in Xinjiang Province, China. ''Yinlong'' was discovered in an upper section of this formation which dates to the

Oxfordian stage The Oxfordian is, in the ICS' geologic timescale, the earliest age of the Late Jurassic Epoch, or the lowest stage of the Upper Jurassic Series. It spans the time between 163.5 ± 1.0 Ma and 157.3 ± 1.0 Ma (million years ago). The Oxfordia ...

of the Late Jurassic, or 161.2 to 155.7 million years ago.Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'
Winter 2010 Appendix.
/ref> Most other described ceratopsians are known from the later

Cretaceous Period 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 t ...

Description

''Yinlong'' was a relatively small dinosaur, reaching in length and in body mass. Despite a virtually frill-less and totally hornless skull, ''Yinlong'' is a ceratopsian. Its skull is deep and wide and relatively large compared to most ornithischians, but also proportionately smaller than most other ceratopsians. Long robust hindlimbs and shorter slender forelimbs with three-fingered hands suggests a bipedal lifestyle like many small ornithopods.

Classification

A small

rostral bone Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic ...

on the end of the upper jaw clearly identifies ''Yinlong'' as a ceratopsian, although the skull displays several features, especially the ornamentation of the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

bone of the skull roof, which were previously thought to be unique to

pachycephalosauria Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycepha ...

ns. The presence of these features in ''Yinlong'' indicates these as actual synapomorphies (unique features) of the larger group

Marginocephalia Marginocephalia (/mär′jə-nō-sə-făl′ē-ən/ Latin: margin-head) is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. There are two clad ...

, which contains both the pachycephalosaurs and the ceratopsians, although these features have been lost in all known ceratopsians more derived than ''Yinlong''. The addition of these characters further strengthens the support for Marginocephalia. ''Yinlong'' also preserves skull features reminiscent of the family

Heterodontosauridae Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group ...

, providing support for the

hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

that heterodontosaurids are closely related to marginocephaliansZhao X., Cheng Z., & Xu X. 1999. "The earliest ceratopsian from the Tuchengzi Formation of Liaoning, China." ''Journal of Vertebrate Paleontology'' 19(4): 681-691.Cooper, M.R. 1985. "A revision of the ornithischian dinosaur ''Kangnasaurus coetzeei'' Haughton, with a classification of the Ornithischia." ''Annals of the South African Museum'' 95: 281-317.You H., Xu X. & Wang X. 2003. "A new genus of Psittacosauridae (Dinosauria: Ornithopoda) and the origin and early evolution of marginocephalian dinosaurs." ''Acta Geologica Sinica (English edition)'' 77: 15–20. The group containing Marginocephalia and Heterodontosauridae has been named Heterodontosauriformes. However, this hypothesis was not supported by a subsequent analysis of basal ornithischians that was carried out as part of a study on the postcranial anatomy of ''Yinlong'', which resolved the below phylogeny of Ceratopsia. Guanlong and Yinlong

Diet

''Yinlong'' was discovered with seven

gastrolith A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In oth ...

s preserved in the abdominal cavity. Gastroliths, stones stored in the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

and used to grind plant material, are also found in other ceratopsians such as ''

Psittacosaurus ''Psittacosaurus'' ( ; "parrot lizard") is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 126 and 101 million years ago. It is notable for being the most species-rich non-avian dinosaur gen ...

'', and are also widely distributed in most other dinosaur groups, including

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 ...

References

External links

GW News Center
featuring a link to the original paper, pictures, and a press release on the discovery of ''Yinlong'' (site operated by

George Washington University The George Washington University (GW or GWU) is a Private university, private University charter#Federal, federally chartered research university in Washington, D.C. Chartered in 1821 by the United States Congress, GWU is the largest Higher educat ...

) {{Taxonbar, from=Q132877 Ceratopsians Ornithischian genera Oxfordian genera Late Jurassic dinosaurs of Asia Jurassic China Fossils of China Paleontology in Xinjiang Fossil taxa described in 2006 Taxa named by Catherine Forster