| Yangchuanosaurus | |
|---|---|
 | |
| Y. shangyouensis skeleton displayed inHong Kong Science Museum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Metriacanthosauridae |
| Genus: | †Yangchuanosaurus Donget al., 1978 |
| Type species | |
| †Yangchuanosaurus shangyouensis Donget al., 1978 | |
| Other species | |
| Synonyms | |
Synonyms ofY. shangyouensis
Synonyms ofY.?zigongensis
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Yangchuanosaurus is anextinctgenus ofmetriacanthosauridtheropoddinosaur that lived inChina from theMiddle Jurassic toLate Jurassic periods (Bathonian toTithonian stages), and was similar (although slightly larger) in size and appearance to itsNorth American andEuropean relative,Allosaurus.Yangchuanosaurus hails from theUpper Shaximiao Formation and was the largestpredator in a landscape that included thesauropodsMamenchisaurus andOmeisaurus and thestegosaursChialingosaurus,Tuojiangosaurus andChungkingosaurus. This theropod was named after the area in which was discovered,Yongchuan, in China.
Donget al. (1978) namedYangchuanosaurus shangyouensis on the basis ofCV 00215, a completeskull andskeleton which was collected from theShangshaximiao Formation, near Yongchuan,Yongchuan District,Sichuan. It dates to theOxfordian stage of theLate Jurassicperiod, about 161.2 to 157.3 million years ago. It was discovered in June 1977 by a construction worker during the construction of theShangyou Reservoir Dam. A second species from the same locality,Y. magnus, was named by Donget al. (1983) on the basis of CV 00216, another complete skull and skeleton. A detailed revision oftetanuran phylogeny by Carrano, Benson & Sampson (2012) revealed that both species are conspecific. Donget al. (1978) and Donget al. (1983) differentiated these species primarily on the basis of size. In addition, Donget al. (1983) noted that the maxilla ofY. magnus has an additional fenestra within the antorbital fossa, whereasY. shangyouensis possessed only a fossa in this location. However, it is considered to be anintraspecific, possiblyontogenetic,variation. Furthermore, the apparent difference incervical vertebral morphology can be explained by comparing different positions within the column. Hence, the holotypes of the two species ofYangchuanosaurus are effectively identical, and their codings are identical in Carranoet al. (2012) matrix.[1]Gregory S. Paul (1988) regarded this genus as a synonym ofMetriacanthosaurus, but this has not been supported.[2]
Y.?hepingensis is a species named by Gao in 1992,[3] but it was subsequently referred to as a species ofSinraptor.[4] However, the identity of this species withinSinraptor is questioned by other paleontologists,[1][5] and Rauhut and colleagues included this species withinYangchuanosaurus based on their phylogenetic analysis in 2019 and 2024 respectively.[6][7]
Carranoet al. (2012) assigned a third specimen toY. shangyouensis. CV 00214 is represented by a partialpostcranial 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 Donget al. (1978) in a faunal list as a new species ofSzechuanosaurus,Szechuanosaurus "yandonensis". There is no description or illustration of it, makingS. "yandonensis" anomen nudum. Later, Donget al. (1983) described it, and assigned it toSzechuanosaurus campi, adubious species which is known only from four teeth. Carranoet al. (2012) noted that CV 00214 can't be assigned toS. campi because the holotype materials ofS. 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 whichSzechuanosaurus zigongensis should also be subsumed. However, Carranoet al. (2012) suggested that CV 00214 and "S."zigongensis cannot be cospecific as there are noautapomorphies shared between them, and the latter derives from the underlyingXiashaximiao Formation. A phylogenetic analysis found CV 00214 to be most closely related toY. shangyouensis, and thus the former is assignable to it. Furthermore,Szechuanosaurus zigongensis was found to be closely related toY. shangyouensis and therefore was designated as a new species ofYangchuanosaurus,[1] though this has been considered questionable by Rauhut and colleagues.[6][7]
Y.?zigongensis is known from four specimens includingZDM 9011 (holotype), a partial postcranial skeleton; ZDM 9012, a leftmaxilla; ZDM 9013, two teeth and ZDM 9014, a right hind limb. It was first described by Gao (1993), and all specimens were collected from theMiddle JurassicXiashaximiao Formation in the Dashanpu Dinosaur Quarry of Zigong, Sichuan.[8]
Another informal species,Yangchuanosaurus "longqiaoensis", was briefly mentioned in a faunal listing of thePenglaizhen 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 anomen nudum and is questionably referable toYangchuanosaurus.[11]
Thetype specimen ofY. shangyouensis had askull 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 speciesY. 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 toCeratosaurus andTameryraptor.
Yangchuanosaurus was a large, powerfulmeat-eater. Itwalked 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 smalldewclaw. The three outer toes were used to bear weight and each was equipped with a large claw.
Aphylogenetic analysis by Carranoet al. (2012) foundYangchuanosaurus to be thebasalmost knownmetriacanthosaurid and the only non-metriacanthosaurine metriacanthosaurid. Thecladogram presented below follows their study.[1]
| Orionides |
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Thecladogram presented below follows Zanno & Makovicky (2013).[5]
| Allosauroidea |
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In 2019, Rauhut and Pol includedY.?hepingensis as a species ofYangchuanosaurus, whileY?zigongensis was recovered as a metriacanthosaurid not closely related toYangchuanosaurus in their phylogenetic analysis.[6] In 2024, Rauhut and colleagues, the describers ofAlpkarakush, included bothY. shangyouensis andY.?hepingensis withinYangchuanosaurus but recoveredY.?zigongensis outside the genus as a basal tetanuran of uncertain taxonomic position based on their phylogenetic analysis.[7]
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