| Yunnanosaurus | |
|---|---|
 | |
| Fossil jaw,Tianjin Natural History Museum | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropodiformes |
| Genus: | †Yunnanosaurus Young, 1942 |
| Type species | |
| †Yunnanosaurus huangi Young, 1942 | |
| Other species | |
Yunnanosaurus (/juːˌnænoʊˈsɔːrəs/yoo-NAN-oh-SOR-əs) is anextinctgenus ofsauropodomorphdinosaur that lived approximately 199 to 183million years ago in what is now theYunnan Province, inChina, for which it was named.Yunnanosaurus was a large sized, moderately-built, ground-dwelling,quadrupedalherbivore, that could also walkbipedally, 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 firstYunnanosaurus skeletons in the upper Zhangjiawa Member of theLufeng Formation ofYunnan,China, dating to theSinemurian stage of theEarly 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 speciesY. huangi (thetype species) andY. robustus.
In 2007,Lü Junchang and colleagues described another species ofYunnanosaurus,Y. youngi (named in honor of C. C. Young). In addition to various skeletal differences, at 13 meters (42 ft) longY. youngi was significantly larger thanY. huangi (which reached only 7 meters [23 ft]). The holotype specimen CXMVZA 185 consists of tencervical vertebrae, fourteendorsal vertebrae, three fusedsacral vertebrae, seventeencaudal vertebrae, both pubic bones, both ischia, and the right ilium. The skull of this species is not known.[1]
The type specimen ofYunnanosaurus youngi was recovered at the Banqing Houshanliangzi locality of theFengjiahe Formation,[2] 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 thePliensbachianstage of theEarly 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 toYunnanosaurus robustus.[Note 1] 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 ofYunnanosaurus huangi reveals very distinctive growth changes.[3]
There were more than sixty spoon-shaped teeth in the jaws ofYunnanosaurus, and were unique among early sauropodomorphs in that its teeth were self-sharpening because they "[wore] against each other as the animal fed."[4] Scientists consider these teeth to be advanced compared to other early sauropodomorphs, as they share features with the sauropods.[4] However, scientists do not considerYunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animal's body are distinctly "prosauropod" in design.[4] This critical difference implies that the similarity in dentition betweenYunnanosaurus and sauropods might be an example ofconvergent evolution.[4]
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Thetype species,Y. huangi, was named byC. C. Young in 1942, who erected the family Yunnanosauridae to contain it, though the family currently comprises only this genus and sometimesJingshanosaurus. The specific name honours Huang Chiching ("T.K. Huang"), the director of the National Geological Survey of China.[6] Young also named a second species,Y. robustus, in 1951,[4][7] but this has since beenincluded in the type species.[4] The confusion in classification arose due to that the earliest specimens ofY. huangi were of juvenile individuals while theY. robustus specimens represented fully grown adults.[4] However, Sekiyaet al. (2013) described a juvenile ofY. robustus and were able to differentiate it fromY. huangi.Yunnanosaurus had been assigned to several taxa over the years, includingThecodontosauridae andPlateosauridae, but a more recent phylogenetic analysis conducted by Novaset al. (2011) shows that this genus is part of the taxonMassopoda in a clade withAnchisaurus andJingshanosaurus.[5] Apaldetti et al. (2011) also found thatYunnanosaurus belonged inMassopoda, but found that this genus was more primitive than bothJingshanosaurus andAnchisaurus.[8]
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.
According to Barrett et al. (2007), the skull ofY. huangi can be distinguished from other sauropodomorphs based on the following characteristics:[9]
Additionally, Sekiyaet al. (2013) add one more character distinguishingY. huangi: a hemispherical neural spine in the posterior cervical vertebrae.[3]
According to Lu et al. (2007),Y. youngi can be distinguished fromY. huangi based on the following characteristics:[1]
According to Sekiya et al. (2013),Yunnanosaurus robustus can be distinguished from other sauropodomorphs based on the following characteristics:[3]
The type specimens ofYunnanosaurus huangi andYunnanosaurus robustus were recovered in the Huangchiatien (Dahungtien) locality of theLufeng Formation in Yunnan, China. TheY. huangiholotype specimen IVPP V20 and theY. robustus holotype specimen IVPP V93, were collected by Chung Chien Young in terrestrial sediments from the upper dark/deep red beds of the Zhangjiawa Member of this formation, that are believed to have been deposited during theSinemurianstage of theJurassic period, approximately 199 to 190 million years ago.[10] Several other specimens assigned toY. huangi (IVPP V54, IVPP V47, IVPP V61, IVPP V62, IVPP V63, IVPP V96, IVPP V264), andY. robustus (IVPP V39, IVPP V94) were also recovered by Young in this locality. These specimens are all housed in the collection of theInstitute of Vertebrate Paleontology and Paleoanthropology, inBeijing, China. In the years to come several more specimens assigned to these two species were recovered from Zhangjiawa Member of this formation.
Chung Chien Young had also explored the lower dark/dull purple beds of the Shawan Member of the Lufeng Formation and found more specimens that he later assigned toY. huangi. Specimen IVPP V32 was collected by Young in 1938 in dark red, argillaceous sandstone that is believed to have been deposited during theHettangianstage of theJurassic period, approximately 201 to 199 million years ago.[10] Specimens IVPP V57, IVPP V60 and IVPP V272 were collected by Young in blue mudstone from the same formation and were also assigned toY. huangi. These specimens from the Shawan Member are also housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology.
Yunnanosaurus huangi andYunnanosaurus robustus shared theirpaleoenvironment with theornithischiansBienosaurus, andTatisaurus, thesauropodomorphsGyposaurus,Lufengosaurus, andJingshanosaurus, and thetheropodsSinosaurus triassicus andEshanosaurus.
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