Shuangbaisaurus

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Shuangbaisaurus
Temporal range: ?Hettangian
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Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Genus:† Shuangbaisaurus
Wang et al., 2017
Type species
†Shuangbaisaurus anlongbaoensis
Wang et al., 2017

Shuangbaisaurus (meaning "Shuangbai reptile") is genus of theropod dinosaur, possibly a junior synonym of Sinosaurus. It lived in the Early Jurassic of Yunnan Province, China, and is represented by a single species, S. anlongbaoensis, known from a partial skull. Like the theropods Dilophosaurus and Sinosaurus,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.

Description

Shuangbaisaurus had a relatively robust (compared to Sinosaurus ) skull, with a length of 54 centimetres (21 in) and a length/height ratio of 2.84, not including the thin paired crests that were present at least above the eye sockets. These crests are incompletely preserved, but appeared to have been formed mostly from the frontal bone, as well as possibly the postorbital and prefrontal bones. The crests may have extended further forward, over the nasal and lacrimal bones. Similar crests are seen in Dilophosaurus and Sinosaurus; however, the crests of Sinosaurus do not extend over the eyes, [1] thus differentiating it from Shuangbaisaurus. [2]

At the tip of the jaw, the premaxilla and maxilla are separated by a groove, which is also a defining characteristic of Sinosaurus. [3] The premaxilla would have been taller than it is long, which is similar to specimen LFGT LDM-L10 of Sinosaurus triassicus but unlike either Dilophosaurus or specimen KMV 8701 of Sinosaurus sinensis. Also like LFGT LDM-L10, the bottom edge of the premaxilla is much higher than the maxilla. The two bones are at the same level in KMV 8701, and are angled away from each other in Dilophosaurus. [1] Similar to both LFGT LDM-L10 and KMV 8701, [3] the maxilla bears a near-vertical front margin; it is lower and more pointed in Dilophosaurus. The front portion of the bottom margin of the maxilla is angled such that the first maxillary tooth projects forwards. There is a groove running parallel to the tooth row along the bottom rim of the maxilla. [2]

From behind, the maxilla is connected to the jugal. The lacrimal is located above their joint, enclosing the fossa that surrounds the antorbital fenestra. There is a ridge directed downwards and backwards on the side of the jugal, like in Zupaysaurus ; [4] this same ridge is horizontal in Sinosaurus and Dilophosaurus. [1] The same is also true of the joint between the jugal and quadratojugal. The quadratojugal tapers to a point underneath the infratemporal fenestra, where it is joined at the back to the quadrate. Further above, the lacrimal is joined by the long and slender descending branch of the three-pronged postorbital, which is convex in its upper third. From above, the forward-directed branch of the postorbital is offset from the backward-directed branch, being separated by a small recess. The frontals appeared to have been long and large, forming most of the top of the skull. [2]

The antorbital fenestra of Shuangbaisaurus is large, occupying roughly one third the length of the skull. The back margin of the fenestra slopes backwards, like LFGT LDM-L10 and Dilophosaurus but unlike KMV 8701. [1] Further behind, the orbit is keyhole-shaped, with a longer back rim compared to the front rim. The infratemporal fenestra is roughly trapezoidal, with a long axis oriented upwards and backwards towards the top of the rear of the skull. On the top surface of the skull, the rounded supratemporal fenestra is unusually small, with a diameter equivalent to only about half of the length on the top of the skull behind the level of the orbit. [2]

Discovery and naming

Shuangbaisaurus is known from a single specimen, a partial skull missing most of the top of the snout, stored at the Chuxiong Prefectural Museum in Chuxiong Yi Autonomous Prefecture, Yunnan, China under the specimen number CPM C2140ZA245. Additionally, the front half and back portion of the jaw are also associated with the skull. The specimen's snout has also become bent to the left due to deformation during fossilization. It was discovered in layers of purple muddy siltstone located in Liuna Village, Anlongbao Town, Shuangbai County, Chuxiong Yi, about 100 kilometres (62 mi) south of the well-known Lufeng deposits. These layers have been recognized as belonging to the Early Jurassic Fengjiahe Formation, [2] which has been tentatively dated to the Hettangian. [5]

In 2017, the type and only species of the genus Shuangbaisaurus, S. anlongbaoensis, was formally described and named by Wang Guo-Fu, You Hai-Lu, Pan Shi-Gang, and Wang Tao. The generic name refers to Shuangbai County, and the specific name refers to Anlongbao Town (with Anlongbao literally meaning "dragon-placing fort"), and thus both elements of the binomial name reference its provenance. [2]

In a 2019 conference abstract, Philip Currie and colleagues suggested that CPM C2140ZA245 fell within the range of variation of specimens assigned to Sinosaurus triassicus. [6]

Classification

After Dilophosaurus and Sinosaurus, Shuangbaisaurus is the third large theropod known definitely to have had paired crests on its skull (though the smaller [7] Coelophysis kayentakatae [8] also has similar crests). Shuangbaisaurus seems to generally be similar to the roughly contemporaneous Sinosaurus. However, they are notably differentiated in that the crests clearly extend over the orbit in Shuangbaisaurus, whereas they are restricted to extensions of the nasal and lacrimal that do not reach past the orbit in Sinosaurus. Similarly, the backward and downward orientation of the jugal is a trait of Shuangbaisaurus not seen in Sinosaurus, where it is horizontal. However, the vertical groove separating the premaxilla and maxilla, which seems to be present in Shuangbaisaurus, was denoted as a distinguishing characteristic of Sinosaurus by Matthew Carrano and colleagues in 2012, [3] thus complicating its referral to a new genus by Wang et al. [2]

A further issue in the relation between Shuangbaisaurus and Sinosaurus involves the taxonomic convolution that has befallen Sinosaurus. At least one species is recognized in the genus, Sinosaurus triassicus, consisting of specimens LFGT LDM-L10 and LFGT ZLJT01; another specimen, KMV 8701, originally named "Dilophosaurus" sinensis, has been referred to either S. triassicus [9] [10] [11] or a second species S. sinensis. [1] KMV 8701 approaches Shuangbaisaurus more closely in its tall skull and premaxilla than specimens referred to S. triassicus. [1] [3] Wang et al. elected to retain S. sinensis as a separate species owing to these differences. No phylogenetic analysis has been conducted to quantitatively determine the relationships of Shuangbaisaurus. [2]

Paleoecology

Aside from Shuangbaisaurus, several sauropodomorph dinosaurs originate from the Fengjiahe Formation. These include Chinshakiangosaurus chunghoensis (a possible sauropod), [5] [12] Lufengosaurus sp. , [13] Yimenosaurus youngi , [12] and Yunnanosaurus huangi (a juvenile specimen, which was also discovered in Shuangbai County). [14] Ostracods of the genus Darwinula have also been found. A diverse ichnofauna is also known from deposits of the Fengjiahe Formation, including the ichnotaxa Eubrontes platypus , Grallator limnosus , Paracoelurosaurichnus monax , Schizograllator xiaohebaensis , Youngichnus xiyangensis , and Zhengichnus jinningensis (with the last four sometimes considered synonymous with Grallator). [13]

Temporally, the Fengjiahe Formation is equivalent to the Lower Lufeng Formation, from where Sinosaurus is known alongside a diverse assemblage consisting of another theropod, Lukousaurus ; sauropodmorphs (including Chinshakiangosaurus sp., Lufengosaurus huenei, L. magnus, Xingxiulong chengi and Yunnanosaurus huangi); ornithischians; crocodylomorphs; cynodonts and mammals; turtles; amphibians; and bivalves. [15] [16]

See also

Related Research Articles

<i>Dilophosaurus</i> Genus of theropod dinosaur from Early Jurassic

Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved were collected in 1942. The most complete specimen became the holotype of a new species in the genus Megalosaurus, named M. wetherilli by Samuel P. Welles in 1954. Welles found a larger skeleton belonging to the same species in 1964. Realizing it bore crests on its skull, he assigned the species to the new genus Dilophosaurus in 1970, as Dilophosaurus wetherilli. The genus name means "two-crested lizard", and the species name honors John Wetherill, a Navajo councilor. Further specimens have since been found, including an infant. Fossil footprints have also been attributed to the animal, including resting traces. Another species, Dilophosaurus sinensis from China, was named in 1993, but was later found to belong to the genus Sinosaurus.

Cryolophosaurus is a genus of large theropod dinosaur known from only a single species Cryolophosaurus ellioti, from the early Jurassic of Antarctica. It was one of the largest theropods of the Early Jurassic, with the subadult being estimated to have reached 6–7 metres (20–23 ft) long and weighed 350–465 kilograms (772–1,025 lb).

<i>Monolophosaurus</i> Extinct genus of dinosaurs

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).

<i>Lufengosaurus</i> Sauropodomorph massospondylid dinosaur genus from Early Jurassic period

Lufengosaurus is a genus of massospondylid dinosaur which lived during the Early Jurassic period in what is now southwestern China.

<i>Yunnanosaurus</i> Extinct genus of dinosaurs

Yunnanosaurus 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.

<i>Sinosaurus</i> Genus of dinosaurs

Sinosaurus is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately 5.5 metres (18 ft) in length and 300 kilograms (660 lb) in body mass. Fossils of the animal were found at the Lufeng Formation, in the Yunnan Province of China.

<i>Zupaysaurus</i> Extinct genus of dinosaurs

Zupaysaurus is an extinct genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. Although a full skeleton has not yet been discovered, Zupaysaurus can be considered a bipedal predator, up to 4 metres (13 ft) long. It may have had two parallel crests running the length of its snout.

<i>Gyposaurus</i> Extinct genus of reptiles

Gyposaurus is a genus of basal sauropodomorph dinosaur from the early Jurassic of South Africa. It is usually considered to represent juveniles of other prosauropods, but "G." sinensis is regarded as a possibly valid species.

<i>Jeholosaurus</i> Extinct genus of dinosaurs

Jeholosaurus is a genus of neornithischian dinosaur from the Early Cretaceous Period. It is thought to have been a herbivorous small ornithopod.

<i>Lukousaurus</i> Extinct species of reptile

Lukousaurus is an archosauromorph based on most of a small skull's snout, displaying distinctive lachrymal horns, found in the Early Jurassic-age Lower Lufeng Formation, Yunnan, China and was described by Chung Chien Young in 1940. The generic name refers to the Lugou Bridge, lit. “crossroads”, near Beijing, where the Sino-Japanese War started. L. yini is tentatively classified as a theropod dinosaur by some allied to ceratosaurs, by others a coelurosaur. Its skull is rather robust for its size though the teeth were described by the author as typically theropodan. Whatever Lukousaurus was, it was definitely an archosauromorph.

The 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.

<i>Duriavenator</i> Genus of theropod dinosaur

Duriavenator is a genus of theropod dinosaur that lived in what is now England during the Middle Jurassic, about 168 million years ago. In 1882, upper and lower jaw bones of a dinosaur were collected near Sherborne in Dorset, and Richard Owen considered the fossils to belong to the species Megalosaurus bucklandii, the first named non-bird dinosaur. By 1964, the specimen was recognised as belonging to a different species, and in 1974 it was described as a new species of Megalosaurus, M. hesperis; the specific name means 'the West' or 'western'. Later researchers questioned whether the species belonged to Megalosaurus, in which many fragmentary theropods from around the world had historically been placed. After examining the taxonomic issues surrounding Megalosaurus, Roger B. J. Benson moved M. hesperis to its own genus in 2008, Duriavenator; this name means "Dorset hunter".

<i>Platyognathus</i> Extinct genus of reptiles

Platyognathus is an extinct genus of protosuchian crocodyliform. Fossils are known from the Early Jurassic Lower Lufeng Formation in Yunnan, China and belong to the type and only species, P. hsui.

<i>Xixiasaurus</i> Genus of dinosaur

Xixiasaurus is a genus of troodontid dinosaur that lived during the Late Cretaceous Period in what is now China. The only known specimen was discovered in Xixia County, Henan Province, in central China, and became the holotype of the new genus and species Xixiasaurus henanensis in 2010. The names refer to the areas of discovery, and can be translated as "Henan Xixia lizard". The specimen consists of an almost complete skull, part of the lower jaw, and teeth, as well as a partial right forelimb.

<i>Sarahsaurus</i> Extinct genus of dinosaurs

Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic period in what is now northeastern Arizona, United States.

Chuxiongosaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic Period. Fossils of this genus have been found in the Lower Lufeng Formation, Yunnan Province, southern China. Identified from the holotype CMY LT9401 a nearly complete skull with some similarities to Thecodontosaurus, it was described as the "first basal sauropod dinosaur from the Early Jurassic of China," more basal than Anchisaurus. It was named by Lü Junchang, Yoshitsugu Kobayashi, Li Tianguang and Zhong Shimin in 2010, and the type species is Chuxiongosaurus lufengensis. It is a possible junior synonym of Jingshanosaurus.

<i>Aorun</i> Extinct genus of dinosaurs

Aorun is a genus of carnivorous theropod dinosaur first discovered in 2006, with its scientific description published in 2013. It is one of the oldest known coelurosaurian dinosaurs and is estimated to have lived ~161.6 million years ago during the Late Jurassic Period. It is the fifth extinct theropod discovered from Wucaiwan, China.

<i>Megapnosaurus</i> Extinct genus of dinosaur

Megapnosaurus is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago during the early part of the Jurassic Period in what is now Africa. The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb). It was originally given the genus name Syntarsus, but that name was later determined to be preoccupied by a beetle. The species was subsequently given a new genus name, Megapnosaurus, by Ivie, Ślipiński & Węgrzynowicz in 2001. Some studies have classified it as a species within the genus Coelophysis, but this interpretation has been challenged by more subsequent studies and the genus Megapnosaurus is now considered valid.

Panguraptor is a genus of coelophysid theropod dinosaur known from fossils discovered in Lower Jurassic rocks of southern China. The type and only known species is Panguraptor lufengensis. The generic name refers to the deity Pangu but also to the supercontinent Pangaea for which in a geological context the same characters are used: 盘古. Raptor means "seizer", "robber" in Latin. The specific name is a reference to the Lufeng Formation. The holotype specimen was recovered on 12 October 2007 from the Lufeng Formation of Yunnan, which is noted for sauropodomorph fossils. It was described in 2014 by You Hai-Lu and colleagues.

<i>Xingxiulong</i> Extinct genus of reptiles

Xingxiulong 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 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.

References

  1. 1 2 3 4 5 6 Xing, L. (2012). Sinosaurus from southwestern China (M.Sc.). University of Alberta.
  2. 1 2 3 4 5 6 7 8 Wang, G.-F.; You, H.-L.; Pan, S.-G.; Wang, T. (2017). "A new crested theropod dinosaur from the Early Jurassic of Yunnan Province, China" (PDF). Vertebrata PalAsiatica. 55 (2): 177–186. Archived from the original (PDF) on 2017-07-29.
  3. 1 2 3 4 Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300. doi:10.1080/14772019.2011.630927. S2CID   85354215.
  4. ↑ Ezcurra, M.D.; Novas, F.E. (2007). "Phylogenetic relationships of the Triassic theropod Zupaysaurus rougieri from NW Argentina". Historical Biology. 19 (1): 35–72. doi:10.1080/08912960600845791. S2CID   84277003.
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  6. ↑ Currie, P.J.; Xing, L.; Wu, X.; Dong, Z. (2019). Murray, A.M.; LeBlanc, A.; Holmes, R.B. (eds.). Anatomy and relationships of Sinosaurus triassicus (Theropoda, Coelophysoidea) from the Lufeng Formation (Lower Jurassic) of Yunnan, China. 7th Annual Meeting of the Canadian Society of Vertebrate Palaeontology. Vertebrate Anatomy Morphology Palaeontology. Vol. 7. p. 17. ISSN   2292-1389.
  7. ↑ Gates, T.A.; Organ, C.; Zanno, L.E. (2016). "Bony cranial ornamentation linked to rapid evolution of gigantic theropod dinosaurs". Nature Communications. 7: 12931. doi:10.1038/ncomms12931. PMC   5052652 . PMID   27676310.
  8. ↑ Rowe, T. (1989). "A New Species of the Theropod Dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona". Journal of Vertebrate Paleontology. 9 (2): 125–136. doi:10.1080/02724634.1989.10011748. JSTOR   4523249.
  9. ↑ Xing, L.D.; Bell, P.R.; Rothschild, B.M.; Ran, H.; Zhang, J.P.; Dong, Z.M.; Zhang, W.; Currie, P.J. (2013). "Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the lower Jurassic strata of the Lufeng Basin, China". Chinese Science Bulletin. 58 (16): 1931–1935. doi: 10.1007/s11434-013-5765-7 .
  10. ↑ Xing, L.; Paulina-Carabajal, A.; Currie, P.J.; Xu, X.; Zhang, J.; Wang, T.; Burns, M.E.; Dong, Z. (2014). "Braincase Anatomy of the Basal Theropod Sinosaurus from the Early Jurassic of China". Acta Geologica Sinica. 88 (6): 1653–1664. doi:10.1111/1755-6724.12335. S2CID   131595322.
  11. ↑ Xing, L.; Wang, Y.; Snively, E.; Zhang, J.; Dong, Z.; Burns, M.E.; Currie, P.J. (2015). "Model-Based Identification of Mechanical Characteristics of Sinosaurus (Theropoda) Crests". Acta Geologica Sinica. 89 (1): 1–11. doi:10.1111/1755-6724.12390. S2CID   128688200.
  12. 1 2 Upchurch, P.; Barrett, P.M.; Zhao, X.; Xu, X. (2007). "A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs". Geological Magazine. 144 (2): 247–262. doi:10.1017/S0016756806003062. S2CID   85775483.
  13. 1 2 Chen, P.-J.; Li, J.; Matsukawa, M.; Zhang, H.; Wang, Q.; Lockley, M.G. (2006). "Geological ages of dinosaur-track-bearing formations in China" (PDF). Cretaceous Research. 27 (1): 22–32. doi:10.1016/j.cretres.2005.10.008.
  14. ↑ Sekiya, T.; Jin, X.; Zheng, W.; Shibata, M.; Azuma, Y. (2013). "A new juvenile specimen of Yunnanosaurus robustus (Dinosauria: Sauropodomorpha) from Early to Middle Jurassic of Chuxiong Autonomous Prefecture, Yunnan Province, China". Historical Biology. 26 (2): 252–277. doi:10.1080/08912963.2013.821702. S2CID   85132483.
  15. ↑ Wang, Y.-M.; You, H.-L.; Wang, T. (2017). "A new basal sauropodiform dinosaur from the Lower Jurassic of Yunnan Province, China". Scientific Reports. 73: 41881. doi:10.1038/srep41881. PMC   5312170 . PMID   28205592.
  16. ↑ Luo, Z.; Wu, X.-C. (1997). "The small tetrapods of the Lower Lufeng Formation, Yunnan, China". In Fraser, N.C.; Sues, H.-D. (eds.). In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge: Cambridge University Press. pp. 251–270. ISBN   9780521458993.
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