Yunnanosaurus

Yunnanosaurus (/ˌjuːnænoʊˈsɔːrəs/ YOO-nan-o-SAWR-əs) is an extinct genus of sauropodomorph dinosaur that lived approximately 201 to 168 million years ago in what is now the Yunnan Province, in China. 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.

Yunnanosaurus
Temporal range: Early Jurassic,
201–168 Ma
Yunnanosaurus-Tianjin Natural History Museum
Fossil jaw, Tianjin Natural History Museum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropodiformes
Genus: Yunnanosaurus
Young, 1942
Type species
Yunnanosaurus huangi
Young, 1942
Other Species

Y. youngi Lu et al., 2007

Discovery

Yunnanosaurus scale
Size of Y. huangi (light green) and Y. youngi (dark green)

Yang Zhongjian (also known as C. C. Young) discovered the first Yunnanosaurus skeletons in the Lufeng Formation of Yunnan, China. The fossil find was composed of over twenty incomplete skeletons, including two skulls, it was excavated by Tsun Yi Wang. When first discovered, Yunnanosaurus was considered to be closely related to Lufengosaurus, but more recent research by Novas et al. (2011) shows that it is most closely related to Anchisaurus and Jingshanosaurus.[1]

Description

Dentition

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."[2] Scientists consider these teeth to be advanced compared to other early sauropodomorphs, as they share features with the sauropods.[2] However, scientists do not consider Yunnanosaurus to be especially close to the sauropods in phylogeny because the remaining portions of the animals body are distinctly "prosauropod" in design.[2] This critical difference implies that the similarity in dentition between Yunnanosaurus and sauropods might be an example of convergent evolution.[2]

Yunnanosaurus youngi

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]). Y. youngi is found later in the fossil record, hailing from the Middle Jurassic. 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 illium. The skull of this species is not known.[3]

Juvenile Specimen ZMNH-M8739

In 2013, Sekiya et al. described the discovery of a juvenile individual which was assigned to what the authors termed "Yunnanosaurus robustus" (i.e. Y. huangi).[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 of Yunnanosaurus huangi reveals very distinctive growth changes.[4]

Classification

 Plateosauria 
 Plateosauridae 

Jaklapallisaurus

Unaysaurus

Plateosaurus engelhardti

Plateosaurus gracilis

Plateosaurus ingens

 Massopoda 
 Riojasauridae 

Eucnemesaurus

Riojasaurus

 Massospondylidae 

Massospondylus

Pradhania

Coloradisaurus

Lufengosaurus

Glacialisaurus

 Anchisauria 

Yunnanosaurus

Jingshanosaurus

Anchisaurus

Melanorosaurus

Sauropoda

The red bracket identifies members of the group "Prosauropoda".
Plateosauria cladogram based on the phylogenetic analysis, conducted by Novas et al., 2011.[1]

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.[5] Young also named a second species, Y. robustus, in 1951,[2][6] but this has since been included in the type species.[2] The confusion in classification arose due to that the earliest specimens of Y. huangi were of juveniles individuals while the "Y. robustus" specimens represented fully grown adults.[2] Yunnanosaurus had been assigned to several taxa over the years, including Thecodontosauridae and Plateosauridae, but 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.[1] Apaldetti et al. (2011) also found that Yunnanosaurus belonged in Massopoda, but found that this genus was more primitive than both Jingshanosaurus and Anchisaurus.[7]

Distinguishing anatomical features

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 Sekiya et al. (2013), Yunnanosaurus can be distinguished from other dinosaurs based on the following characteristics:

  • the absence of the anteroposterior expansion on the medial end of the astragalus
  • the medium shaft of the metatarsal IV is dorsoventrally compressed

According to Lu et a. (2007), Yunnanosaurus youngi can be distinguished from Yunnanosaurus huangi based on the following characteristics:

  • the sixth cervical vertebra is the longest among the vertebral column
  • the neural spines of the posterior cervical vertebrae are short with an expanded distal end, which is wider than its anteroposterior length
  • three sacral vertebrae are tightly fused with a stout sacrocostal yoke
  • the ventral margin of the postacetabular process of the ilium is slightly concave
  • the ischium is longer than the pubis
  • the distal end of the pubis is round

Paleoecology

Provenance and occurrence

The type specimens of Yunnanosaurus huangi and Yunnanosaurus robustus were recovered in the Huangchiatien (Dahungtien) locality of the Lufeng Formation in Yunnan, China. The Y. huangi holotype specimen IVPP V20 and the Y. 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 the Sinemurian stage of the Jurassic period, approximately 199 to 190 million years ago.[8] Several other specimens assigned to Y. huangi (IVPP V54, IVPP V47, IVPP V61, IVPP V62, IVPP V63, IVPP V96, IVPP V264), and Y. robustus (IVPP V39, IVPP V94) were also recovered by Young in this locality. These specimens are all housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing, 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 to Y. huangi. Specimen IVPP V32 was collected by Young in 1938 in dark red, argillaceous sandstone that is believed to have been deposited during the Hettangian stage of the Jurassic period, approximately 201 to 199 million years ago.[8] Specimens IVPP V57, IVPP V60 and IVPP V272 were collected by Young in blue mudstone from the same formation and were also assigned to Y. huangi. These specimens from the Shawan Member are also housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology.

The type specimen of Yunnanosaurus youngi was recovered at the Banqing Houshanliangzi locality of 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 Aalenian and Bajocian stages of the Middle Jurassic period, approximately 174 to 168 million years ago. This specimen is housed in the collection of the Chuxiong Museum.

Fauna and habitat

Yunnanosaurus huangi and Yunnanosaurus robustus shared their paleoenvironment with the ornithischians Bienosaurus, and Tatisaurus, the sauropodomorphs Gyposaurus, Lufengosaurus, and Jingshanosaurus, and the theropods Sinosaurus triassicus and Eshanosaurus.

Notes

  1. ^ An unfused neural arch and long bone surface texture that is finely grooved, suggest that this individual is a juvenile.

References

  1. ^ a b c Fernando E. Novas, Martin D. Ezcurra, Sankar Chatterjee and T. S. Kutty (2011). "New dinosaur species from the Upper Triassic Upper Maleri and Lower Dharmaram formations of central India". Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101 (3-4): 333–349. doi:10.1017/S1755691011020093
  2. ^ a b c d e f g "Yunnanosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 47. ISBN 0-7853-0443-6.
  3. ^ Lu, J., Li, T., Zhong, S., Azuma, Y., Fujita, M., Dong, Z., and Ji, Q. (2007). "New yunnanosaurid dinosaur (Dinosauria, Prosauropoda) from the Middle Jurassic Zhanghe Formation of Yuanmou, Yunnan Province of China." Memoir of the Fukui Prefectural Dinosaur Museum, 6: 1-15.
  4. ^ Toru Sekiya, Xingsheng Jin, Wenjie Zheng, Masateru Shibata & Yoichi Azuma (2013) A new juvenile specimen of Yunnanosaurus robustus (Dinosauria: Sauropodomorpha) from Early to Middle Jurassic of Chuxiong Autonomous Prefecture, Yunnan Province, China. Historical Biology (advance online publication) DOI:10.1080/08912963.2013.821702
  5. ^ Young, C. C. (1942). "Yunnanosaurus huangi Young (gen. et sp. nov.), a new Prosauropoda from the red beds at Lufeng, Yunnan." Bulletin of the Geological Society of China, 22 (1-2): 63-104.
  6. ^ Young, C. C. (1951). "The Lufeng saurischian fauna in China." Paleontologica Sinica, ser. C, 13: 1-96.
  7. ^ Cecilia Apaldetti, Ricardo N. Martinez, Oscar A. Alcober and Diego Pol (2011). Claessens, Leon (ed.). "A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina". PLoS ONE. 6 (11): e26964. doi:10.1371/journal.pone.0026964. PMC 3212523. PMID 22096511.CS1 maint: Multiple names: authors list (link)
  8. ^ a b Luo, Z., and X.-C. Wu. 1994. The small tetrapods of the Lower Lufeng Formation, Yunnan, China; pp. 251–270 in N. C. Fraser and H.-D.Sues (eds.), In the Shadow of the Dinosaurs. Cambridge University Press, New York
1942 in paleontology

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1942.

Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Avetheropoda

Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.

Bajocian

In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian age succeeds the Aalenian age and precedes the Bathonian age.

Cerapoda

Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Lower Lufeng Series

The Lower Lufeng Series (or Lower Lufeng Formation) is a Lower Jurassic sedimentary rock formation found in Yunnan, China. It has two units: the lower Dull Purplish Beds/Shawan Member are of Hettangian age, and Dark Red Beds/Zhangjia'ao Member are of Sinemurian age. It is known for its fossils of early dinosaurs. The Dull Purplish Beds have yielded the possible therizinosaur Eshanosaurus, the possible theropod Lukousaurus, and the "prosauropods" "Gyposaurus" sinensis, Lufengosaurus, Jingshanosaurus, and Yunnanosaurus. Dinosaurs discovered in the Dark Red Beds include the theropod Sinosaurus triassicus, the "prosauropods" "Gyposaurus", Lufengosaurus, and Yunnanosaurus, indeterminate remains of sauropods, and the early armored dinosaurs Bienosaurus and Tatisaurus.

Lufengosaurus

Lufengosaurus (Chinese: 祿豐龍 or 禄丰龙, meaning "Lufeng lizard") is a genus of massospondylid dinosaur which lived during the Early Jurassic period in what is now southwestern China. The dinosaur made international headlines in 2017 when Nature Communications reported scientists' discovery of 195-million-year-old collagen protein in the rib of a Lufengosarus fossil.

Lü Junchang

Lü Junchang (Chinese: 吕君昌; 1965 – 9 October 2018) was a Chinese palaeontologist and professor at the Institute of Geology, Chinese Academy of Geological Sciences. An expert on Mesozoic reptiles, he described and named dozens of dinosaur and pterosaur taxa including Tongtianlong, Qianzhousaurus, Heyuannia, Gannansaurus, Yunnanosaurus youngi, and Darwinopterus.

Massospondylidae

Massospondylidae is a family of early massopod dinosaurs that existed in Asia, Africa, South America and Antarctica during the Late Triassic to the Early Jurassic periods. Several dinosaurs have been classified as massospondylids over the years. The largest cladistic analysis of early sauropodomorphs, which was presented by Apaldetti and colleagues in November 2011, found Adeopapposaurus, Coloradisaurus, Glacialisaurus, Massospondylus, Leyesaurus and Lufengosaurus to be massospondylids. This result supports many previous analyses that tested fewer taxa. However, this analysis found the two recently described North American massopods, Sarahsaurus and Seitaad, and the South African Ignavusaurus to nest outside Massospondylidae, as opposed to some provisional proposals. Earlier in 2011, Pradhania, a sauropodomorph from India, was tested for the first time in a large cladistic analysis and was found to be a relatively basal massospondylid. Mussaurus and Xixiposaurus may also be included within Massospondylidae. In 2019, a specimen previously assigned to Massospondylus from South Africa was re-examined and found to belong to a separate genus that was named Ngwevu.

Mussaurus

Mussaurus (meaning "mouse lizard") is a genus of herbivorous sauropodomorph dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since Mussaurus is now known from adult specimens, the name is something of a misnomer; adults possibly reached 6 metres (20 ft) in length and weighed more than 1,000 kilograms (2,200 lb). Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.

Orionides

Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.

Plateosauria

Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s.

Plateosauria is a node-based taxon. In 1998, Paul Sereno defined Plateosauria as the last common ancestor of Plateosaurus engelhardti and Massospondylus carinatus, and its descendants. Peter Galton and Paul Upchurch in 2004 used a different definition: the last common ancestor of Plateosaurus engelhardti and Jingshanosaurus xinwaensis, and its descendants. In their cladistic analysis the Plateosauria belonged to the Prosauropoda, and included the Plateosauridae subgroup. In Galton's and Upchurch's study also Coloradisaurus, Euskelosaurus, Jingshanosaurus, Massospondylus, Mussaurus, Sellosaurus, and Yunnanosaurus proved to be plateosaurians.However, recent cladistic analyses suggest that the Prosauropoda as traditionally defined is paraphyletic to sauropods. Prosauropoda, as currently defined, is a synonym of Plateosauridae as both contain the same taxa by definition.

The following cladogram simplified after an analysis presented by Apaldetti and colleagues in 2011.

The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.

Plateosauridae

Plateosauridae is a family of plateosaurian sauropodomorphs from the Late Triassic of Europe. Although several dinosaurs have been classified as plateosaurids over the years, the family Plateosauridae is now restricted to Plateosaurus. In another study, Yates (2003) sunk Sellosaurus into Plateosaurus (as P. gracilis).

Pulanesaura

Pulanesaura is an extinct genus of basal sauropod known from the Early Jurassic (late Hettangian to Sinemurian) Upper Elliot Formation of the Free State, South Africa. It contains a single species, Pulanesaura eocollum, known from partial remains of at least two subadult to adult individuals.

Shuangbaisaurus

Shuangbaisaurus (meaning "Shuangbai reptile") is an extinct genus of theropod dinosaur, possibly a dilophosaurid, that lived in the Early Jurassic of Yunnan Province, China. It contains a single species, S. anlongbaoensis, represented by a partial skull. Like the theropods Dilophosaurus and Sinosaurus, the latter of which was its contemporary, Shuangbaisaurus bore a pair of thin, midline crests on its skull. Unusually, these crests extended backwards over the level of the eyes, which, along with the unusual orientation of the jugal bone, led the describers to name it as a new genus. However, Shuangbaisaurus also possesses a groove between its premaxilla and maxilla, a characteristic which has been used to characterize Sinosaurus as a genus. Among the two morphotypes present within the genus Sinosaurus, Shuangbaisaurus more closely resembles the morphotype that is variably treated as a distinct species, S. sinensis, in its relatively tall skull.

Xingxiulong

Xingxiulong (meaning "Xingxiu Bridge dragon") is a genus of bipedal sauropodiform from the Early Jurassic of China. It contains a single species, X. chengi, described by Wang et al. in 2017 from three specimens, two adults and an immature individual, that collectively constitute a mostly complete skeleton. Adults of the genus measured 4–5 metres (13–16 ft) long and 1–1.5 metres (3 ft 3 in–4 ft 11 in) tall. Phylogenetic analysis suggests that Xingxiulong is most closely related to its contemporary Jingshanosaurus, although an alternative position outside of both the Sauropodiformes and Massospondylidae is also plausible.

Despite their close relationship, Xingxiulong prominently differs from Jingshanosaurus - and from most basal sauropodomorphs - in having a number of sauropod-like traits. These include a sacrum containing four vertebrae; a pubis with an exceptionally long top portion; and the femur, the first and fifth metatarsals on the foot, and the scapula being wide and robust. These probably represent adaptations to supporting high body weight, in particular a large gut. Unlike sauropods, however, Xingxiulong would still have been bipedal.

Yang Zhongjian

Yang Zhongjian (Chinese: 杨钟健; Wade–Giles: Yang Chung-chien; 1 June 1897 – 15 January 1979), courtesy name Keqiang (克强), also known as C.C. (Chung Chien) Young, was one of China's foremost vertebrate paleontologists. He has been called the "Father of Chinese Vertebrate Paleontology".

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