Jiangjunosaurus
| Jiangjunosaurus Temporal range: Late Jurassic,
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| Genus: | Jiangjunosaurus Jia, Forster, Xu & Clark, 2007
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Jiangjunosaurus is a genus of herbivorous stegosaurid dinosaur from the Oxfordian-age (Upper Jurassic) Shishugou Formation of the Junggar Basin, Xinjiang, China.
Discovery and naming
In 2002, Liu Yongfei discovered the remains of a stegosaurian. These were secured by a Sino-American expedition and prepared by Xiang Lishi and Ding Xiaoqing.[1]
The type species, Jiangjunosaurus junggarensis, was named and described by Jia Chengkai, Catherine Foster, Xu Xing and James Clark in 2007. The generic name refers to the abandoned town of Jiangjunmiao. Jiangjun, 將 軍, is "general" in Chinese and the town's name has been explained by the burial of one. The specific name refers to the provenance from the Junggar.[1]
The holotype, IVPP V 14724, was found in a layer of the Shishugou Formation, dating from the Oxfordian. It includes the lower jaws, some rear skull bones, eleven neck vertebrae, ribs, a scapula, a coracoid, and two neck plates. These elements were found in almost perfect articulation. It represents a subadult individual.[1]
Description
In 2010, Gregory S. Paul estimated that Jiangjunosaurus reached around six metres (twenty feet) in length and weighed 2.5 tonnes.[2]
The describers established three distinguishing traits. The crowns of the teeth are symmetrical and in side view wider than tall. The spine of the axis, the second neck vertebra, has a rectangular profile in side view, instead of a triangular one. The rear neck vertebrae have large vein openings in their sides.[1]
The skull of Jiangjunosaurus is relatively elongated, the maximum width above the postorbitals probably measuring 35% of the skull length. There are at least fourteen teeth in the maxilla. The quadratojugal has a robust horizontal front branch and a thin short vertical branch, only half as tall as the quadratum shaft. There is no clear foramen paraquadraticum, opening between the quadratum and quadratojugale. The quadratum is inclined to the rear and has a depression on its flange contacting the pterygoid. There is no clear opening between the front branches of the pterygoids.[1]
The predentary, the bone core of the lower beak placed on the fronts of both lower jaws, has a deep and hooked "chin". Between the predentary and the tooth row a gap is present equal to about four tooth positions. From the rear part of a bone shelf at the outside of the tooth row a vertical plate extends upwards obscuring that row in side view. The plate continues into a high coronoid process. Between dentary, surangular and angular a rather tall triangular mandibular fenestra is present.[1]
The dentary bears twenty-one teeth, which are slightly larger than those of the upper jaws. All teeth of Jiangjunosaurus are symmetrical with a triangular profile. Front and rear edges have both seven denticles. In side view the teeth are broad, about as wide as tall. Both their inner and outer sides are convexly curved from the front to the rear. The usual vertical ridges are present but weakly developed; the frontmost and rearmost teeth lack them completely. Primary vertical ridges in the middle are absent.[1]
Of the neck vertebrae the second, the axis, has a neural spine or processus spinosus that is rectangular in side view, due to a higher than normal front edge. It is elongated and rather low. From the fifth cervical vertebra onwards large depressions appear on the lower rear side of the vertebral body. These are pierced by large openings that become progressively wider further back in the series. These foramina are superficially very similar to the pneumatic openings with Saurischia. However, CAT-scans of the Jiangjunosaurus fossils revealed that the openings are not connected to inner air spaces and thus probably served as vein channels. Some dorsal ribs have a crescent-shaped flange at their lower ends.[1]
Phylogeny
Jiangjunosaurus was placed in the Stegosauridae in 2007. The describers concluded that within the Stegosauridae it had a basal position. This was not based on an exact cladistic analysis but on the method of comparative anatomy.[1]
Paleobiology
Jiangjunosaurus may have been a prey item for the large metriacanthosaurid theropod Yangchuanosaurus.[2]
References
- ^ a b c d e f g h i Chengkai, Jia (2007). "The first stegosaur (Dinosauria, Ornithischia) from the Upper Jurassic Shishugou Formation of Xinjiang, China". Acta Geologica Sinica (English edition). 81 (3): 351–356. doi:10.1111/j.1755-6724.2007.tb00959.x.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b Paul, Gregory S. The Princeton Field Guide to Dinosaurs. Princeton University Press, 2010.
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