Yuanmousaurus
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Yuanmousaurus Temporal range: Middle Jurassic |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | Saurischia |
| Suborder: | †Sauropodomorpha |
| Family: | †Mamenchisauridae |
| Genus: |
†Yuanmousaurus Lu et al., 2006 |
| Species: | †Y. jingyiensis |
| Binomial name | |
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Yuanmousaurus jingyiensis Lu et al., 2006 |
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Yuanmousaurus ("Yuanmou lizard") was a sauropod dinosaur from the Middle Jurassic period of China. It is known from incomplete remains, recovered in 2000 from the Zhanghe Formation in Yuanmou County in Yunnan Province. Yuanmousaurus was a relatively large sauropod and may have reached about 17 meters (56 ft) in length. It was a basal member of the Sauropoda, but its exact systematic position is unclear. A recent study placed Yuanmousaurus within the family Mamenchisauridae. The only and type species was Yuanmousaurus jiangyiensis.
Yuanmousaurus was estimated to be approximately 17 meters (56 ft) in length. The skull is missing, while the neck is known only from a fragment of a posterior cervical vertebra. This fragment indicates elongated neck vertebrae, similar to those of mamenchidaurid sauropods, but unlike the much shorter neck vertebrae of the more basal Shunosaurus. From the trunk and tail, 9 dorsal, 3 sacral and 7 caudal vertebrae were found. While the shoulder- and pelvic girdle are missing with the exception of one ilium, the limbs are better known, including the humerus, ulna, radius, thigh bone, tibia, fibula, astragalus, and a claw from the hind foot. The forelimbs were proportionally longer than in the shortnecked Shunosaurus, but shorter than in Omeisaurus: the length ratio between humerus and thigh bone was 0.72 in Yuanmousaurus, while it was 0.56 in Shunosaurus and 0.80 in Omeisaurus.
Yuanmousaurus is deemed to be a basal member of the Eusauropoda, standing outside the Neosauropoda, which comprises all more derived sauropods. In its species description, Lu Junchang and colleagues considered Yuanmousaurus a member of the Euhelopodidae that was closely related to Patagosaurus, more basal than Euhelopus, and more derived than Omeisaurus. The Euhelopodidae, however, is abandoned by many palaeontologists since the systematic position of Euhelopus itself is controversial. A newer analysis by Toru Sekiya places Yuanmousaurus within the Mamenchisauridae, together with Mamenchisaurus, Tienshanosaurus and Chuanjiesaurus.
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