In 1979 and 1980, two specimens were discovered of a small herbivorous dinosaur during excavations near Dashanpu in Sichuan. In 1983 Dong Zhiming and Tang Zilu named the fossils under the type species Xiaosaurus dashanpensis. The generic name is derived from Chinese xiáo, 曉, "dawn", a reference to the age of the fossil. The specific name refers to Danshanpu.
The holotype, IVPP V6730A, was found in the lower Xiashaximiao Formation of which the age is uncertain: both the Bajocian and the Bathonian–Callovian have been proposed. It consists of a partial skeleton including a jaw fragment with a single tooth, two cervical vertebrae, four caudal vertebrae, a humerus, a partial left femur and a complete right hindlimb. The paratype IVPP V6730B is a second partial skeleton including a right femur, a dorsal vertebra, two sacral vertebrae, a phalanx, a rib and two teeth.
Xiaosaurus was a small bipedal animal with an estimated length of one metre. The femur is 11 centimetres (4.3 in) long.
The remains are too fragmentary to easily classify the genus. The describers assigned it both to the Fabrosauridae and the Hypsilophodontidae, considering it an evolutionary link between Lesothosaurus and Hypsilophodon. Xiaosaurus has sometimes been considered a nomen dubium and an ornithischian of uncertain affinities, possibly a basal cerapod or marginocephalian. However, Paul Barrett et al. in 2005 concluded it to be provisionally valid, as it possessed a single unique derived trait or autapomorphy: a mediolaterally (seen from the front) straight humerus.
Temporal range: Middle Jurassic
Dong & Tang, 1983
Dong & Tang, 1983
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.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.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Datousaurus
Datousaurus, meaning "Big-head Lizard" (from the Chinese da tou "Big Head" and Greek sauros/σαυρος "lizard") was a dinosaur from the Middle Jurassic. It was a sauropod collected from the Lower Shaximiao Formation in Dashanpu, Zigong Sichuan province, China. It shared the local Middle Jurassic landscape with other sauropods such as Shunosaurus, Omeisaurus, Protognathosaurus, the ornithopod Xiaosaurus, the early stegosaur Huayangosaurus as well as the carnivorous Gasosaurus.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Haya griva
Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.Huayangosaurus
Huayangosaurus is a genus of stegosaurian dinosaur from the Middle Jurassic of China. The name derives from "Huayang" (華陽), an alternate name for Sichuan (the province where it was discovered), and "saurus", meaning "lizard". It lived during the Bathonian to Callovian stages, around 165 million years ago, some 20 million years before its famous relative, Stegosaurus appeared in North America. At only 4.5 metres long, it was also much smaller than its famous cousin. Found in the Lower Shaximiao Formation, Huayangosaurus shared the local Middle Jurassic landscape with the sauropods Shunosaurus, Datousaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the carnivorous Gasosaurus. It was found in Huayang in China.Jeholosauridae
Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Melanorosauridae
The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.Neornithischia
Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Raeticodactylidae
Raeticodactylidae is a family of eudimorphodontoid eopterosaurian pterosaurs that lived in Switzerland during the Late Triassic. The family includes Caviramus, and the type genus Raeticodactylus, which are both known from the Kössen Formation, around 205 mya. Raeticodactylidae was first used in 2014 by Andres et al., as a group of all pterosaurs closer to Raeticodactylus than Eudimorphodon. The following phylogenetic analysis follows the topology of Andres et al. (2014).Riojasauridae
Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).Xixiposaurus
Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.Zigong Dinosaur Museum
The Zigong Dinosaur Museum (simplified Chinese: 自贡恐龙博物馆; traditional Chinese: 自貢恐龍博物館; pinyin: Zìgòng Kǒnglóng Bówùguǎn) is located near the city of Zigong, Sichuan, China, in the township of Dashanpu. The museum sits on top of a large concentration of a diverse dinosaur assemblage from the Dashanpu Formation. The museum claims the largest number of dinosaur fossils in the world and covers 25,000 square meters with a display area of 3,600 square meters. It attracts up to seven million visitors a year.In 1980s, vast quantities of dinosaur fossils were excavated in the Middle Jurassic Dashanpu Formation, 7 km north-east from downtown Zigong, including a dinosaur named after the township, Dashanpusaurus. Because of the unique and articulated (intact) bone remains, Zigong is important to paleontologists and dinosaur enthusiasts. The Zigong Dinosaur Museum was established in 1987, becoming the first museum based almost entirely on dinosaurs in Asia. Mounted specimens include Omeisaurus, Gigantspinosaurus, Yangchuanosaurus, Huayangosaurus and Xiaosaurus.