''Xiaosaurus'' ("dawn lizard", ), 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 small

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

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 middle

Jurassic 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 ...

, approximately 169 to 163.5 mya. ''Xiaosaurus'' lived in what is now the

Sichuan Basin The Sichuan Basin (), formerly transliterated as the Szechwan Basin, sometimes called the Red Basin, is a lowland region in southwestern China. It is surrounded by mountains on all sides and is drained by the upper Yangtze River and its tributar ...

of China.

Discovery and naming

In 1979 and 1980, two specimens were discovered of a small herbivorous dinosaur during excavations near

Dashanpu The Shaximiao Formation () is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around th ...

Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestant missions) is a province in Southwest China occupying most of the ...

. In 1983

Dong Zhiming Dong Zhiming (Chinese: 董枝明, Pinyin: ''Dǒng Zhimíng''; born January 1937) is a Chinese vertebrate paleontologist formerly employed at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing. He began working at th ...

and Tang Zilu named the fossils under 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 ...

''Xiaosaurus dashanpensis''. The generic name is derived from

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 ...

''xiáo'', 曉, "dawn", a reference to the age of the fossil. The specific name refers to Danshanpu. 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 sever ...

, IVPP V6730A, was found in the lower

Xiashaximiao Formation The Shaximiao Formation () is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around th ...

of which the age is uncertain: both the

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stra ...

and the

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Str ...

–

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

have been proposed. It consists of a partial skeleton including a jaw fragment with a single tooth, two cervical

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e, four caudal vertebrae, a humerus, a partial left

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 wit ...

and a complete right hindlimb. The

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

IVPP V6730B is a second partial skeleton including a right femur, a dorsal vertebra, two sacral vertebrae, a

phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar pole weapons. The term is particularly ...

, a rib and two teeth. In 1992

Peng Guangzhao Peng may refer to: * Peng (surname) (彭), a Chinese name * Peng (state) (大彭), a state during the late Shang dynasty * Peng (mythology) (鵬), a legendary Chinese creature * ''Peng!'', 1992 album by Stereolab * ''PENG!'', a 2005 comic * P.Eng. ...

renamed ''

Agilisaurus ''Agilisaurus'' (; 'agile lizard') is a genus of ornithischian dinosaur from the Middle Jurassic Period of what is now eastern Asia. It was about 3.5–4 ft (1.2-1.7 m) long, 2 ft (0.6 m) in height and 40 kg in weight. It has ...

multidens'' He & Cai 1983 (now ''

Hexinlusaurus ''Hexinlusaurus'' is a genus of basal ornithischian dinosaur from the Middle Jurassic of China. The holotype (ZDM T6001, Zigong Dinosaur Museum, Dashanpu, People's Republic of China), consists of an almost complete, articulated skull and some ...

'') into a second species of ''Xiaosaurus'': ''Xiaosaurus multidens'', but this has not been accepted.

Description

''Xiaosaurus'' was a small bipedal animal with an estimated length of one metre. The femur is long.

Classification

The remains are too fragmentary to easily classify the genus. The describers assigned it both to the Fabrosauridae and the Hypsilophodontidae, considering it an

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary link between ''

Lesothosaurus ''Lesothosaurus'' is a Monotypic taxon, monospecific genus of ornithischian dinosaur that lived during the Early Jurassic in what is now South Africa and Lesotho. It was named by paleontologist Peter Galton in 1978, the name meaning "lizard from L ...

'' and ''

Hypsilophodon ''Hypsilophodon'' (; meaning "''Hypsilophus''-tooth") is a neornithischian dinosaur genus from the Early Cretaceous period of England. It has traditionally been considered an early member of the group Ornithopoda, but recent research has put thi ...

''. ''Xiaosaurus'' has sometimes been considered a '' nomen dubium'' and an ornithischian of uncertain affinities, possibly a basal cerapod or

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 ...

n. However,

Paul Barrett Paul Franklyn "Legs" Barrett (14 December 1940 – 20 January 2019) was a UK agent and manager of 1950s style Rock and Roll artistes, an author and previously a singer, songwriter and film actor. Barrett is the discoverer, mentor and first ma ...

''et al.'' in 2005 concluded it to be provisionally valid, as it possessed a single unique derived trait or

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

: a mediolaterally (seen from the front) straight humerus.Barrett, P.M., Butler, R.J., and Knoll, F. 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. ''Journal of Vertebrate Paleontology'' 25(4):823-834

Notes

References

DinoDictionary.com's entry for ''Xiaosaurus''
Ornithischian genera Bajocian genus first appearances Bathonian genera Callovian genus extinctions Middle Jurassic dinosaurs of Asia Taxa named by Dong Zhiming Fossil taxa described in 1983 Paleontology in Sichuan {{ornithischian-stub