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Yangchuanosaurus

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Yangchuanosaurus
Temporal range: 168.3–145 Ma
Y. shangyouensis skeleton displayed in Hong Kong Science Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Metriacanthosauridae
Genus: †Yangchuanosaurus
Dong et al., 1978
Type species
†Yangchuanosaurus shangyouensis
Dong et al., 1978
Other species
  • †Y.? hepingensis
    (Gao, 1992)
  • †Y.? zigongensis
    (Gao, 1993)
Synonyms
Synonyms of Y. shangyouensis
  • Yangchuanosaurus magnus
    Dong, Zhou & Zhang, 1983
  • Szechuanosaurus "yandonensis"
    Dong et al., 1978
  • "Szechuanoraptor dongi"
    Chure, 2001
  • Metriacanthosaurus shangyouensis
    Paul, 1988
Synonyms of Y.? zigongensis
  • Szechuanosaurus zigongensis
    Gao, 1993
  • Metriacanthosaurus carpenteri
    Paul, 1988

Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China from the Middle Jurassic to Late Jurassic periods (Bathonian to Tithonian stages), and was similar in size and appearance to its North American and European relative, Allosaurus. Yangchuanosaurus hails from the Upper Shaximiao Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. This theropod was named after the area in which was discovered, Yongchuan, in China.

Discovery and species

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Mounted skeleton of Y. zigongensis, Delaware Museum of Natural History

Dong et al. (1978) named Yangchuanosaurus shangyouensis on the basis of CV 00215, a complete skull and skeleton which was collected from the Shangshaximiao Formation, near Yongchuan, Yongchuan District, Sichuan. It dates to the Oxfordian stage of the Late Jurassic period, about 161.2 to 157.3 million years ago. It was discovered in June 1977 by a construction worker during the construction of the Shangyou Reservoir Dam. A second species from the same locality, Y. magnus, was named by Dong et al. (1983) on the basis of CV 00216, another complete skull and skeleton. A detailed revision of tetanuran phylogeny by Carrano, Benson & Sampson (2012) revealed that both species are conspecific. Dong et al. (1978) and Dong et al. (1983) differentiated these species primarily on the basis of size. In addition, Dong et al. (1983) noted that the maxilla of Y. magnus has an additional fenestra within the antorbital fossa, whereas Y. shangyouensis possessed only a fossa in this location. However, it is considered to be an intraspecific, possibly ontogenetic, variation. Furthermore, the apparent difference in cervical vertebral morphology can be explained by comparing different positions within the column. Hence, the holotypes of the two species of Yangchuanosaurus are effectively identical, and their codings are identical in Carrano et al. (2012) matrix.[1] Gregory S. Paul (1988) regarded this genus as a synonym of Metriacanthosaurus, but this has not been supported.[2]

Additional specimens

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Life reconstruction of Y. shangyouensis

Y.? hepingensis is a species named by Gao in 1992,[3] but it was subsequently referred to as a species of Sinraptor.[4] However, the identity of this species within Sinraptor is questioned by other paleontologists,[1][5] and Rauhut and colleagues included this species within Yangchuanosaurus based on their phylogenetic analysis in 2019 and 2024 respectively.[6][7]

Carrano et al. (2012) assigned a third specimen to Y. shangyouensis. CV 00214 is represented by a partial postcranial skeleton lacking the skull. It was collected in the Wujiaba Quarry, near Zigong city, Sichuan, from the lower part of the Shangshaximiao Formation. CV 00214 was initially listed by Dong et al. (1978) in a faunal list as a new species of Szechuanosaurus, Szechuanosaurus "yandonensis". There is no description or illustration of it, making S. "yandonensis" a nomen nudum. Later, Dong et al. (1983) described it, and assigned it to Szechuanosaurus campi, a dubious species which is known only from four teeth. Carrano et al. (2012) noted that CV 00214 can't be assigned to S. campi because the holotype materials of S. campi (IVPP V.235, V.236, V.238, V.239; teeth) are non-diagnostic and no teeth are preserved in CV 00214. A recent restudy of CV 00214 by Daniel Chure (2001) concluded that it represented a new taxon, informally named "Szechuanoraptor dongi", into which Szechuanosaurus zigongensis should also be subsumed. However, Carrano et al. (2012) suggested that CV 00214 and "S." zigongensis cannot be cospecific as there are no autapomorphies shared between them, and the latter derives from the underlying Xiashaximiao Formation. A phylogenetic analysis found CV 00214 to be most closely related to Y. shangyouensis, and thus the former is assignable to it. Furthermore, Szechuanosaurus zigongensis was found to be closely related to Y. shangyouensis and therefore was designated as a new species of Yangchuanosaurus,[1] though this has been considered questionable by Rauhut and colleagues.[6][7]

Y.? zigongensis is known from four specimens including ZDM 9011 (holotype), a partial postcranial skeleton; ZDM 9012, a left maxilla; ZDM 9013, two teeth and ZDM 9014, a right hind limb. It was first described by Gao (1993), and all specimens were collected from the Middle Jurassic Xiashaximiao Formation in the Dashanpu Dinosaur Quarry of Zigong, Sichuan.[8]

Another informal species, Yangchuanosaurus "longqiaoensis", was briefly mentioned in a faunal listing of the Penglaizhen Formation (initially believed to date to the Late Jurassic but is probably Early Cretaceous (Berriasian – Valanginian) in age)[9] by Li, Zhang and Cai (1999).[10] However, since it was published solely in a faunal list and not described in detail, it is a nomen nudum and is questionably referable to Yangchuanosaurus.[11]

Description

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Size of two Y. shangyouensis specimens compared to a human

The type specimen of Y. shangyouensis had a skull 82 centimeters (2.69 ft) long, and its total body length was estimated at 8 meters (26 ft).[12] Another specimen, assigned to the new species Y. magnus, was even larger, with a skull length of 1.11 meters (3.6 ft).[13] It may have been up to 10.8 meters (35 ft) long, and weighed as much as 3.4 metric tons (3.7 short tons).[2] Gregory S. Paul suggested that these are the same species and gave a length of 11 meters (36 feet) and a weight of 3 metric tons (3.3 short tons).[14] There was a bony ridge on its nose and multiple hornlets and ridges, similar to Ceratosaurus.

Yangchuanosaurus was a large, powerful meat-eater. It walked on two large, muscular legs, had short arms, a strong, short neck, a big head with powerful jaws, and large, serrated teeth. It had a long, massive tail that was about half of its length. The first digit of its foot was a small dewclaw. The three outer toes were used to bear weight and each was equipped with a large claw.

Classification

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Mounted skeletons of Yangchuanosaurus and Tuojiangosaurus, Beijing Museum of Natural History
Life reconstruction of Y. shangyouensis

A phylogenetic analysis by Carrano et al. (2012) found Yangchuanosaurus to be the basalmost known metriacanthosaurid and the only non-metriacanthosaurine metriacanthosaurid. The cladogram presented below follows their study.[1]

Orionides

The cladogram presented below follows Zanno & Makovicky (2013).[5]

Allosauroidea

In 2019, Rauhut and Pol included Y.? hepingensis as a species of Yangchuanosaurus, while Y? zigongensis was recovered as a metriacanthosaurid not closely related to Yangchuanosaurus in their phylogenetic analysis.[15] In 2024, Saurophaganax was recovered as a sister taxon of Y. shangyouensis.[16] In the same year, Rauhut and colleagues, the describers of Alpkarakush, included both Y. shangyouensis and Y.? hepingensis within Yangchuanosaurus but recovered Y.? zigongensis outside the genus as a basal tetanuran of uncertain taxonomic position based on their phylogenetic analysis.[7]

References

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Wikimedia Commons has media related to Yangchuanosaurus.
  1. ^ a b c d 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. Bibcode:2012JSPal..10..211C. doi:10.1080/14772019.2011.630927. S2CID 85354215.
  2. ^ a b Paul, Gregory S. (1988). "Eustreptospondylids and Metriacanthosaurs". Predatory Dinosaurs of the World. Simon & Schuster. pp. 286–93. ISBN 0-671-61946-2.
  3. ^ Gao, Yuhui (1992). "Yangchuanosaurus hepingensis – a new species of carnosaur from Zigong, Sichuan" (PDF). Vertebrata PalAsiatica. 30 (4): 313–324.
  4. ^ Currie, Phillip J.; Zhao, Xi-Jin (1993). "A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People's Republic of China" (PDF). Canadian Journal of Earth Sciences. 30 (10): 2037–2081. doi:10.1139/e93-179.
  5. ^ a b Zanno, L. E.; Makovicky, P. J. (2013). "Neovenatorid theropods are apex predators in the Late Cretaceous of North America". Nature Communications. 4: 2827. Bibcode:2013NatCo...4.2827Z. doi:10.1038/ncomms3827. PMID 24264527.
  6. ^ a b Oliver W. M. Rauhut; Diego Pol (2019). "Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs". Scientific Reports. 9 (1): Article number 18826. Bibcode:2019NatSR...918826R. doi:10.1038/s41598-019-53672-7. PMC 6906444. PMID 31827108.
  7. ^ a b c Rauhut, Oliver W M; Bakirov, Aizek A; Wings, Oliver; Fernandes, Alexandra E; Hübner, Tom R (August 1, 2024). "A new theropod dinosaur from the Callovian Balabansai Formation of Kyrgyzstan". Zoological Journal of the Linnean Society. 201 (4). doi:10.1093/zoolinnean/zlae090. ISSN 0024-4082.
  8. ^ Gao, Y. (1993). A new species of Szechuanosaurus from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Vertebrata PalAsiatica 31(4): 308-314.
  9. ^ Huang, Diying (January 1, 2019). "Jurassic integrative stratigraphy and timescale of China". Science China Earth Sciences. 62 (1): 223–255. Bibcode:2019ScChD..62..223H. doi:10.1007/s11430-017-9268-7. ISSN 1869-1897. S2CID 134359019.
  10. ^ Li; Zhang; Cai (1999). "The Characteristics of the Composition of the Trace Elements in Jurassic Dinosaur Bones and Red Beds in Sichuan Basin". Geological Publishing House, Beijing: 155.
  11. ^ "Neotheropoda". www.theropoddatabase.com. Retrieved November 10, 2022.
  12. ^ Dong, Zhiming; Zhang, Yihong; Li, Xuanmin; Zhou, Shiwu (1978). "A new carnosaur from Yongchuan County, Sichuan Province" (PDF). Ke Xue Tong Bao. 23 (5): 302–04.
  13. ^ Dong, Zhiming; Shiwu, Zhou; Zhang, Yihong (1983). "Dinosaurs from the Jurassic of Sichuan" (PDF). Palaeontologia Sinica, New Series C. 162 (23): 1–136.
  14. ^ Paul, Gregory S. (2016). The princeton field guide to dinosaurs 2nd edition. New Jersey: Princeton University Press. pp. 97–99.
  15. ^ Oliver W. M. Rauhut; Diego Pol (2019). "Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs". Scientific Reports. 9 (1): Article number 18826. Bibcode:2019NatSR...918826R. doi:10.1038/s41598-019-53672-7. PMC 6906444. PMID 31827108.
  16. ^ Cau, A. (2024). "A Unified Framework for Predatory Dinosaur Macroevolution". Bollettino della Società Paleontologica Italiana. 63 (1). doi:10.4435/BSPI.2024.08. Supplementary Material
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