|Skull (IVPP V12530)|
Xu et al., 2000
Xu et al., 2000
The first two Jeholosaurus specimens were found in 2000 at Lujiatun near Beipiao City, Liaoning Province, China, and named and described the same year by Xu Xing, Wang Xioalin and You Hailu. The type and only known species is Jeholosaurus shangyuanensis. The generic name Jeholosaurus means "lizard from Jehol"; Jehol is the name of a historical province situated in western Liaoning and northern Hebei. The specific name refers to the geographical area of Shangyuan where the fossil site is located.
The type specimen of Jeholosaurus, on which the genus is based, is IVPP V 12529. It was found in a layer of the early Yixian Formation, dating from the early Aptian, about a 126 million years old. The layers consist of fluvial sandstone interspersed with tuff and it is thought that an enormous volcanic eruption occurred burying everything within a fifty to sixty mile radius. The holotype contains a compressed skull and a partial postcranial skeleton. The second specimen, IVPP V 12530, was referred to the species. It consists of a better preserved, perhaps smaller, skull and some neck vertebrae. Both specimens represent juvenile or at least subadult individuals.
Jeholosaurus was a small bipedal herbivore. Because the specimens are juvenile it is hard to ascertain the adult size. The holotype is 71.1 centimetres (28.0 in) long with a 35.6 centimetres (14.0 in) long tail, nearly half the length of the complete animal. The length of the skull is 6.3 centimetres (2.5 in) and the lower jaws of the mandible are 5.9 centimetres (2.3 in) each. The forelimbs are 25.4 centimetres (10.0 in) long and the hindlimbs are 33 centimetres (13 in). The femur is 9 centimetres (3.5 in) long and the tibia is 10.7 centimetres (4.2 in).
Both skulls are incomplete and had to be partially restored. The referred specimens shows an extremely large orbit compared to the skull size, with a length of 40% of the total skull length. Its snout is short, also comprising 40% of the skull length. Both traits are indicative of a juvenile individual.
The premaxilla has six teeth and the maxilla has at least thirteen teeth. Although the back, maxillary, teeth are fan-shaped like those of a plant eater, the front premaxillary teeth are narrower and longer, more like a carnivorous dinosaur. This may mean that Jeholosaurus was omnivorous, eating both plants and animals. The deeply inset ventral margin in the maxilla suggests fleshy cheeks may have been present. The nasals have large foramina dorsolaterally and a midline fossa. No palpebrae are preserved. Though cervical vertebrae and caudal vertebrae have been preserved, their exact number is unknown. The femur is bowed and has an anterior trochanter slightly lower than the greater trochanter and a third as narrow as the latter. They are separated by a shallow cleft. Between the condyles of the lower femur the (anterior) extensor groove is absent. The fourth trochanter is pendant and located in a rather high position. The foot has four metatarsals. The longest is metatarsal III with a length of 5.5 centimetres (2.2 in); it is placed more anteriorly than the other metatarsals. Metatarsal I is more posterior and its upper part is transversely reduced to a splint.
Some distinguishing traits of Jeholosaurus include: enlarged laterodorsal nasal foramina; a quadratojugal fenestra more than 25% maximum quadratojugal length; a quadratojugal less than 30% of skull height; a predentary with almost 150% of premaxillary body length; a dentary extending posteriorly almost to the posterior border of the angular; and the claw of the third toe being longer than the other third toe phalanges.
Jeholosaurus is an ornithischian, as is shown by its ornithischian four-pronged pelvic structure with a pubis bone pointing downward and backwards, parallel to the ischium, while a forward-pointing prepubic process supports the abdomen.
The describers did not assign Jeholosaurus to any family, limiting themselves to a placement as Ornithischia incertae sedis. Using the comparative method, they pointed out some similarities to basal Euornithopoda: a small antorbital fenestra; the foramen on the quadratojugal; a large quadratic foramen; and the absence of an external fenestra in the lower jaw. However, they also noticed more derived euornithopod traits, such as the form of the greater and anterior trochanter of the thighbone, although the premaxilla not reaching the lacrimal, the high jaw joint and the premaxilla being on the same level as the maxilla, were again basal traits. The fused mandibular symphysis might indicate a relation with the Marginocephalia. Very basal ornithischian traits included the presence of six teeth in the premaxilla with only a short toothless sector in front and a short hiatus with the maxillary teeth.
The following cladogram was based on analysis by Zheng and colleagues in 2009.
Albertadromeus is an extinct genus of orodromine parksosaurid dinosaur known from the upper part of the Late Cretaceous Oldman Formation (middle Campanian stage) of Alberta, Canada. It contains a single species, Albertadromeus syntarsus.Averostra
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.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Changchunsaurus
Changchunsaurus (meaning "Changchun lizard") is an extinct genus of small herbivorous parksosaurid dinosaur from Early Cretaceous deposits of Gongzhuling, Jilin, China. It is the first named dinosaur genus from Jilin.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.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.Koreanosaurus
Koreanosaurus (meaning "Korean lizard") is a genus of ornithopod dinosaur. One species has been described, Koreanosaurus boseongensis.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.Ornithischia
Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "of a bird", and ischion (ἴσχιον), plural ischia, meaning "hip joint". However, birds are only distantly related to this group as birds are theropod dinosaurs.Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, pachycephalosaurids and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there is much debate over whether these filaments found in specimens of Tianyulong, Psittacosaurus, and Kulindadromeus may have been primitive feathers.Orodrominae
Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.Parksosauridae
Parksosauridae is a clade or family of small ornithischians which have previously been generally allied to hypsilophodontids. Parksosauridae is often considered a synonym of Thescelosauridae, but the two groups cannot be synonyms because Parksosauridae is defined as a stem, while Thescelosauridae is defined as a node.Thescelosaurinae
Thescelosaurinae is a subfamily of ornithischian dinosaurs from the Early Cretaceous of Asia and the Late Cretaceous of North America.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.Yueosaurus
Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.