Yangchuanosaurus

Yangchuanosaurus Temporal range: Late Jurassic, 175.6–154 Ma PreЄ Є O S D C P T J K Pg N
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Y. zigongensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Clade:	†Carnosauria
Family:	†Metriacanthosauridae
Genus:	†Yangchuanosaurus Dong et al., 1978
Type species
†Yangchuanosaurus shangyouensis Dong et al., 1978
Species
†Y. shangyouensis Dong et al., 1978 †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 Synonyms of Y. zigongensis: Szechuanosaurus zigongensis Gao, 1993

Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China during the late Oxfordian (and possibly Kimmeridgian) stage of the Late Jurassic, and was similar in size and appearance to its North American contemporary, Allosaurus. It hails from the Upper Shaximiao Formation and was the largest predator in a landscape which included the sauropods Mamenchisaurus and Omeisaurus as well as the Stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. It got its name after its discovery site in Yongchuan, in China.

Description

Artist's impression of Yangchuanosaurus shangyouensis

The type specimen of Y. shangyouensis had a skull long, and its total body length was estimated at about . Another specimen, assigned to the new species Y. magnus, was even larger, with a skull length of . It may have been up to long, and weighed as much as . 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. Its feet had three toes, each with a large claw. Its arms were short, and it had three clawed fingers on each hand.

Discovery and species

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 or the early Kimmeridgian stage of the Late Jurassic period, about 161.2-154 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 cospecific. 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. Gregory S. Paul (1988) regarded this genus as the same as Metriacanthosaurus, but this has not been supported.

File:Yangchuanosaurus shangyouensis.JPG

Yangchuanosaurus shangyouensis skeleton displayed in Hong Kong Science Museum.

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 4 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, the most recent revision (by Carrano et al. (2012)) suggested that CV 00214 and "S." zigongensis can't be cospesific 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 the second species of Yangchuanosaurus.

Yangchuanosaurus 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. 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.

Orionides	Megalosauroidea Avetheropoda Coelurosauria Lourinhanosaurus Other coelurosaurians Allosauroidea Allosauria Allosauridae Carcharodontosauria Neovenatoridae Carcharodontosauridae Metriacanthosauridae Yangchuanosaurus Y. zigongensis Y. shangyouensis CV 00214 CV 00215 and CV 00216 Metriacanthosaurinae Shidaisaurus Metriacanthosaurus "Sinraptor" hepingensis Sinraptor dongi Siamotyrannus

File:Yangchuanosaurus shangyouensis et Tuojiangosaurus multispinus.jpg

Yangchuanosaurus attacking Tuojiangosaurus

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

Allosauroidea

Metriacanthosauridae Yangchuanosaurus zigongensis CV 00214 Yangchuanosaurus shangyouensis Shidaisaurus jinae "Sinraptor" hepingensis Metriacanthosaurus parkeri Sinraptor dongi Siamotyrannus isanensis Allosauria Allosauridae Allosaurus fragilis Saurophaganax maximus Carcharodontosauria Neovenatoridae Neovenator salerii Chilantaisaurus tashuikouensis Megaraptora Siats meekerorum Australovenator wintonensis Fukuiraptor kitadaniensis Aerosteon riocoloradensis Megaraptor namunhuaiquii Carcharodontosauridae Eocarcharia dinops Concavenator corcovatus Acrocanthosaurus atokensis Shaochilong maortuensis Carcharodontosaurinae Carcharodontosaurus saharicus Giganotosaurini Tyrannotitan chubutensis Giganotosaurus carolinii Mapusaurus roseae

References

• Fantastic Facts About Dinosaurs (ISBN 0-7525-3166-2)