Jeholosaurus
| Jeholosaurus Temporal range: Early Cretaceous
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| Jeholosaurus shangyuanensis skeleton reconstruction (Dinosaurland, Lyme Regis). | |
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| Genus: | Jeholosaurus
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| Species: | J. shangyuanensis
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| Binomial name | |
| Jeholosaurus shangyuanensis Xu et al., 2000
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Jeholosaurus is a genus of ornithischian dinosaur from the Early Cretaceous Period. It is thought to have been a small ornithopod presumably related to the hypsilophodonts, and an herbivore. Although the back teeth are like those of a plant eater, the front premaxillary teeth are sharp and pointed like a carnivorous dinosaur. This may mean that Jeholosaurus was omnivorous, eating both plants and animals.
History and discovery
The first Jeholosaurus specimens were found in 2000 in China. The actual fossil site is located in the Yixian Formation, near Beipiao City, Liaoning Province, China. Jeholosaurus was found in a 130 million year old sandstone and it is thought that an enormous volcanic eruption occurred burying everything within a 50-60 mile radius. The name Jeholosaurus means "lizard from Jehol"; Jehol refers to the name of an old geographical area in western Liaoning and northern Hebei. The type and only known species is Jeholosaurus shangyuanensis. The generic name honors Shangyuan where it was first discovered.
Size
The type specimen of Jeholosaurus, on which the genus is based, is IVPP V 12529. It 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 dinosaur. The length of the skull is 6.3 centimetres (2.5 in) and the mandibles are 5.9 centimetres (2.3 in) each. The front legs are 25.4 centimetres (10.0 in) long and the back legs are 33 centimetres (13 in). The femur is 9 centimetres (3.5 in) long and the tibia is 10.7 centimetres (4.2 in).[1]
Anatomy
Most of the specimens had incomplete skulls and had to be restored. Some of the specimens have extremely large orbits compared to the skull size. The snout is short which means those specimens are probably those of juvenile Jeholosaurus. The premaxilla has six teeth and the maxilla has at least thirteen teeth. The deeply inset ventral margin in the maxilla suggests cheeks may have been present. The nasals have large foramina dorsolaterally and a midline fossa. No palpebrae are preserved. The specimens have cervical vertebrae and caudal vertebrae. The femur is bowed and has an anterior trochanter slightly lower than the greater trochanter and a third as wide as the latter. They are separated by a shallow cleft and the extensor groove is absent. The fourth trochantor is pendent. The foot has four metatarsals and the longest is metatarsal III with a length of 5.5 centimetres (2.2 in) and it is placed more anteriorly than the other metatarsals. Metatarsal I is more posterior and metatarsal I is reduced to a splint. Jeholosaurus had enlarged laterodorsal nasal foramina; quadratojugal fenestra more than 25% maximum quadratojugal length; quadratojugal less than 30% of skull height; predentary almost 150% of premaxillary body length; dentary extends posteriorly almost to posterior border of angular.[1]
Classification
The Jeholosaurus pubis bone points downward and toward the tail (backwards), parallel with the ischium, with a forward-pointing process to support the abdomen. This makes a four-pronged pelvic structure similar to the ornithischian hip bone. This description placed Jeholosaurus under the order Ornithischia.[1]
Jeholosaurus is not fully classified and more studies have to be done, but for the present time it was placed into the Hypsilophodontidae family for the following reasons:
- The premaxilla of Jeholosaurus had fairly elongated and deeply concave subnarial process which is seen in hypsilophodonts.
- There are six teeth extend along the premaxilla which is the same number as Lesothosaurus had, but these teeth are slender and recurved without denticles, as in the hypsilophodonts Zephyrosaurus and Thescelosaurus.
- The maxilla has an antorbital fossa about 14% of the cranial length and a small antorbital fenestra located posteriorly, and this is similar to the condition in hypsilophodonts.
- The posterior jugal process expands distally, similar to Yandusaurus.
- The postorbital and frontal are typical of basal hypsilophodonts.
- A round fenestra penetrates the bone, as in hypsilophodonts.[1]
Phylogeny
The following cladogram was based on analysis by Zheng and colleagues in 2009. It placed Jeholosaurus in the order Ornithischia, family Hypsilophodontidae.[2]
| Ornithischia |
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References
- ^ a b c d Xu, Wang and You, 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4)318-325.
- ^ Zheng, X-.T., You, H.-L., Xu, X. and Dong, Z.-M. (2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures." Nature, 458(19): 333-336.
- Ornithopoda from Thescelosaurus.com
