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Yunnanosaurus
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Yunnanosaurus
Yunnanosaurus (/juːˌnænoʊˈsɔːrəs/ yoo-NAN-oh-SOR-əs) is an extinct genus of sauropodomorph dinosaur that lived approximately 199 to 183 million years ago in what is now the Yunnan Province, in China, for which it was named. Yunnanosaurus was a large sized, moderately-built, ground-dwelling, quadrupedal herbivore, that could also walk bipedally, and ranged in size from 7 meters (23 feet) long and 2 m (6.5 ft) high to 4 m (13 ft) high in the largest species.
Yang Zhongjian (also known as C. C. Young) discovered the first Yunnanosaurus skeletons in the upper Zhangjiawa Member of the Lufeng Formation of Yunnan, China, dating to the Sinemurian stage of the Early Jurassic. The fossil find was composed of over twenty incomplete skeletons, including two skulls, it was excavated by Tsun Yi Wang. These remains were the basis for the species Y. huangi (the type species) and Y. robustus.
In 2007, Lü Junchang and colleagues described another species of Yunnanosaurus, Y. youngi (named in honor of C. C. Young). In addition to various skeletal differences, at 13 meters (42 ft) long Y. youngi was significantly larger than Y. huangi (which reached only 7 meters [23 ft]). The holotype specimen CXMVZA 185 consists of ten cervical vertebrae, fourteen dorsal vertebrae, three fused sacral vertebrae, seventeen caudal vertebrae, both pubic bones, both ischia, and the right ilium. The skull of this species is not known.
The type specimen of Yunnanosaurus youngi was recovered at the Banqing Houshanliangzi locality of the Fengjiahe Formation, previously thought to be from the Zhanghe Formation, in Yuanmou County of Yunnan Province, China. The holotype specimen CXMVZA 185 was collected in 2000 in terrestrial sediments deposited during the Pliensbachian stage of the Early Jurassic period, approximately 191 to 183 million years ago. This specimen is housed in the collection of the Chuxiong Museum.
In 2013, Sekiya et al. described the discovery of a juvenile individual which was assigned to Yunnanosaurus robustus. Specimen ZMNH-M8739 consists of partial cranial material and an almost complete post-cranial skeleton. This individual possesses characteristic dentition that suggests a potentially unique feeding mechanism as evidenced a tooth–tooth wear facet on its mesial maxillary and dentary teeth, and maxillary teeth that have coarse serrations. Comparison of this juvenile specimen with adult specimens of Yunnanosaurus huangi reveals very distinctive growth changes.
There were more than sixty spoon-shaped teeth in the jaws of Yunnanosaurus, and were unique among early sauropodomorphs in that its teeth were self-sharpening because they "[wore] against each other as the animal fed." Scientists consider these teeth to be advanced compared to other early sauropodomorphs, as they share features with the sauropods. However, scientists do not consider Yunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animal's body are distinctly "prosauropod" in design. This critical difference implies that the similarity in dentition between Yunnanosaurus and sauropods might be an example of convergent evolution.
The type species, Y. huangi, was named by C. C. Young in 1942, who erected the family Yunnanosauridae to contain it, though the family currently comprises only this genus and sometimes Jingshanosaurus. The specific name honours Huang Chiching ("T.K. Huang"), the director of the National Geological Survey of China. Young also named a second species, Y. robustus, in 1951, but this has since been included in the type species. The confusion in classification arose due to that the earliest specimens of Y. huangi were of juvenile individuals while the Y. robustus specimens represented fully grown adults. However, Sekiya et al. (2013) described a juvenile of Y. robustus and were able to differentiate it from Y. huangi. Yunnanosaurus had been assigned to several taxa over the years, including Thecodontosauridae and Plateosauridae, but a more recent phylogenetic analysis conducted by Novas et al. (2011) shows that this genus is part of the taxon Massopoda in a clade with Anchisaurus and Jingshanosaurus. Apaldetti et al. (2011) also found that Yunnanosaurus belonged in Massopoda, but found that this genus was more primitive than both Jingshanosaurus and Anchisaurus.
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism.
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Yunnanosaurus
Yunnanosaurus (/juːˌnænoʊˈsɔːrəs/ yoo-NAN-oh-SOR-əs) is an extinct genus of sauropodomorph dinosaur that lived approximately 199 to 183 million years ago in what is now the Yunnan Province, in China, for which it was named. Yunnanosaurus was a large sized, moderately-built, ground-dwelling, quadrupedal herbivore, that could also walk bipedally, and ranged in size from 7 meters (23 feet) long and 2 m (6.5 ft) high to 4 m (13 ft) high in the largest species.
Yang Zhongjian (also known as C. C. Young) discovered the first Yunnanosaurus skeletons in the upper Zhangjiawa Member of the Lufeng Formation of Yunnan, China, dating to the Sinemurian stage of the Early Jurassic. The fossil find was composed of over twenty incomplete skeletons, including two skulls, it was excavated by Tsun Yi Wang. These remains were the basis for the species Y. huangi (the type species) and Y. robustus.
In 2007, Lü Junchang and colleagues described another species of Yunnanosaurus, Y. youngi (named in honor of C. C. Young). In addition to various skeletal differences, at 13 meters (42 ft) long Y. youngi was significantly larger than Y. huangi (which reached only 7 meters [23 ft]). The holotype specimen CXMVZA 185 consists of ten cervical vertebrae, fourteen dorsal vertebrae, three fused sacral vertebrae, seventeen caudal vertebrae, both pubic bones, both ischia, and the right ilium. The skull of this species is not known.
The type specimen of Yunnanosaurus youngi was recovered at the Banqing Houshanliangzi locality of the Fengjiahe Formation, previously thought to be from the Zhanghe Formation, in Yuanmou County of Yunnan Province, China. The holotype specimen CXMVZA 185 was collected in 2000 in terrestrial sediments deposited during the Pliensbachian stage of the Early Jurassic period, approximately 191 to 183 million years ago. This specimen is housed in the collection of the Chuxiong Museum.
In 2013, Sekiya et al. described the discovery of a juvenile individual which was assigned to Yunnanosaurus robustus. Specimen ZMNH-M8739 consists of partial cranial material and an almost complete post-cranial skeleton. This individual possesses characteristic dentition that suggests a potentially unique feeding mechanism as evidenced a tooth–tooth wear facet on its mesial maxillary and dentary teeth, and maxillary teeth that have coarse serrations. Comparison of this juvenile specimen with adult specimens of Yunnanosaurus huangi reveals very distinctive growth changes.
There were more than sixty spoon-shaped teeth in the jaws of Yunnanosaurus, and were unique among early sauropodomorphs in that its teeth were self-sharpening because they "[wore] against each other as the animal fed." Scientists consider these teeth to be advanced compared to other early sauropodomorphs, as they share features with the sauropods. However, scientists do not consider Yunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animal's body are distinctly "prosauropod" in design. This critical difference implies that the similarity in dentition between Yunnanosaurus and sauropods might be an example of convergent evolution.
The type species, Y. huangi, was named by C. C. Young in 1942, who erected the family Yunnanosauridae to contain it, though the family currently comprises only this genus and sometimes Jingshanosaurus. The specific name honours Huang Chiching ("T.K. Huang"), the director of the National Geological Survey of China. Young also named a second species, Y. robustus, in 1951, but this has since been included in the type species. The confusion in classification arose due to that the earliest specimens of Y. huangi were of juvenile individuals while the Y. robustus specimens represented fully grown adults. However, Sekiya et al. (2013) described a juvenile of Y. robustus and were able to differentiate it from Y. huangi. Yunnanosaurus had been assigned to several taxa over the years, including Thecodontosauridae and Plateosauridae, but a more recent phylogenetic analysis conducted by Novas et al. (2011) shows that this genus is part of the taxon Massopoda in a clade with Anchisaurus and Jingshanosaurus. Apaldetti et al. (2011) also found that Yunnanosaurus belonged in Massopoda, but found that this genus was more primitive than both Jingshanosaurus and Anchisaurus.
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism.
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