Szechuanosaurus

Szechuanosaurus ("Szechuan lizard") is an extinct genus of carnivorous theropod dinosaur from the Late Jurassic. Fossils referred to the genus have been found in China, Asia in the Oxfordian-?Tithonian (Peng et al., 2005).[1] Its type species is based on several undiagnostic teeth from the Kuangyuan Series.[2][3] Additional possible specimens of Szechuanosaurus were also reported from the Kalaza Formation,[4] also located in China.

Szechuanosaurus
Temporal range: Late Jurassic,
Illustration of a partial tooth
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Neotheropoda
Genus: †Szechuanosaurus
Young, 1942
Type species
†Szechuanosaurus campi
Young, 1942

Szechuanosaurus is at times regarded as a nomen dubium[5][6] due to the lack of diagnostic features in the fossilized teeth upon which the genus is based.[7] Although the fossils are too fragmentary for confident identification, Szechuanosaurus is often interpreted as a medium-sized allosaurid[8] or perhaps a metriacanthosaurid,[6] capable of reaching lengths of around 7.3 meters.[6]

Discovery and species
Speculatively reconstructed skeleton at the Kunming Museum

Three species have been assigned to this genus over the years. The type species is Szechuanosaurus campi, named by Yang Zhongjian ("Chung Chien Young") in 1942 for four isolated tooth specimens: IVPP V235, two partial teeth; IVPP V236, a partial tooth; IVPP V238, several tooth fragments; and IVPP V239, a single tooth. The teeth form a syntype series and were not found together. Also a very fragmentary skeleton, specimen UCMP 32102, was referred to the genus by Yang.[2] Some of the teeth indicate a large body-size. These fossils, although possibly metriacanthosaurid, are now considered to be non-diagnostic, making S. campi a nomen dubium.[9][10] The generic name refers to Szechuan. The specific name honours the American paleontologist Charles Lewis Camp who had discovered UCMP 32102.[11]

A partial skeleton, CV 00214, was initially listed by Dong et al. (1978) in a faunal list as a new species of Szechuanosaurus, Szechuanosaurus yandonensis.[12] At first, there was no description or illustration of it, making S. yandonensis at the time a nomen nudum. Later, Dong Zhiming et alii (1983) described it, and assigned it to Szechuanosaurus campi[13] The affinities of this skeleton are uncertain, and it has only been briefly described. Holtz et al. (2004) included it in their phylogenetic analysis and found it to be the most basal tetanuran.[14] This individual was a medium-sized theropod, with an ischium (a pelvic bone) of 420 millimetres (17 in); for comparison, an ischium of Piatnitzkysaurus estimated to weigh 504 kilograms (1,111 lb) is 423 millimetres (16.7 in) long.[10] In 2000, Daniel Chure referred the specimen to "Szechuanoraptor dongi", itself an invalid nomen ex dissertatione.[15] Carrano, Benson & Sampson (2012) synonymized it with Yangchuanosaurus shangyouensis from the same formation.[16]

The third species is Szechuanosaurus zigongensis, named by Gao Yuhui in 1993 for an almost complete skeleton, specimen ZDM 9011.[17] It is an older species, from the Middle Jurassic, appearing to be distinct from the type species and therefore requires its own genus name.[10] It was reassigned to Yangchuanosaurus, as a Yangchuanosaurus zigongensis, by Matthew Carrano, Roger Benson & Scott Sampson in 2012.[16]

Notes
  1. Peng, G.Z., Ye, Y., Gao, Y.H., Shu, C.K., Jiang, S. (2005): Jurassic dinosaur faunas in Zigong. Sichuan People’s Publishing House, 236 pp
  2. Young, C.C., 1942, "Fossil vertebrates from Kuangyuan, N. Szechuan, China", Bulletin of the Geological Society of China, 22: 293-309
  3. "Table 4.1," in Weishampel, et al. (2004). Page 78.
  4. "Table 13.1," in Weishampel, et al. (2004). Page 263.
  5. Sadleir, R. (2008). The Anatomy and Systematics of Eustreptospondyllus Oxoniensis, a Theropod Dinosaur from the Middle Jurassic of Oxfordshire, England. Palaentographical Society. p. 61.
  6. Molina-Pérez, Rubén; Larramendi, Asier; Connolly, David; Cruz, Gonzalo Ángel Ramírez (2019). Dinosaur Facts and Figures: The Theropods and Other Dinosauriformes. Princeton University Press. p. 260. ISBN 978-0-691-18031-1.
  7. Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004). The Dinosauria, Second Edition. University of California Press. p. 94. ISBN 978-0-520-94143-4.
  8. Lucas, Spencer G. (2002). Chinese Fossil Vertebrates. Columbia University Press. pp. 141–142. ISBN 978-0-231-50461-4.
  9. X.-C. Wu, P. J. Currie, Z. Dong, S. Pan, and T. Wang. 2009. A new theropod dinosaur from the Middle Jurassic of Lufeng, Yunnan, China. Acta Geologica Sinica 83(1):9-24
  10. Brusatte, S. L., Benson, R. B. J., and Xu, X. 2010. "The evolution of large-bodied theropod dinosaurs during the Mesozoic in Asia". Journal of Iberian Geology, 36: 275-296
  11. Camp, C.L., 1935, "Dinosaur remains from the Province of Szechuan", Bulletin of the Department of Geology of the Univiversity of California 23: 467-471
  12. Dong, Z., Chang, Li & Zhou, 1978, "Note on a new carnosaur Yanchuangosaurus shangyuanensis gen. et sp. nov.) from the Jurassic of Yangchuan District, Szechuan Province", Kexue Tongabao 5: 302-304
  13. Dong, Z-M., Zhou, S., Zhang, Y. (1983): [The dinosaurian remains of Sichuan Basin, China]. Palaeontologica Sinica (new series C), 23: 1–145 [in Chinese with English summary].
  14. Holtz, T.R., Molnar, R.E., Currie P.J. (2004): Basal Tetanurae. In: D.B. Weishampel, P. Dodson, P., H. Osmólska (ed.), The Dinosauria, 2nd edn. University of California Press, Berkeley, 71-110
  15. Chure, D.J. (2000) A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (UT–CO) and a revision of the theropod family Allosauridae. Unpublished Ph.D. dissertation, Columbia University, New York
  16. 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.
  17. Gao, Y., 1993, "A new species of Szechuanosaurus from the Middle Jurassic of Dashanpu, Zigong, Sichuan", Vertebrata PalAsiatica 31(4): 308-314

References
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