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| Yuanmouraptor jinshajiangensis Zou, Chen, T. Wang, G.-F. Wang, W.-G. Zhang, X.-Q. Zhang, Z.-J. Wang, Wu & You, 2025 |
Abstract
Metriacanthosaurid theropods represent a basal-branching lineage of tetanurans. Members of this clade are mainly medium to large-sized and lived in Laurasia during the Middle Jurassic to the Early Cretaceous. In this clade, Sinraptor dongi, Sinraptor hepingensis, and Yangchuanosarus shangyouensis from the Late Jurassic are well represented by the nearly complete specimens, but the incompleteness of Middle Jurassic taxa hinders our knowledge of the origin and early evolution of Metriacanthosauridae. This paper describes a new genus and species of metriacanthosaurids, Yuanmouraptor jinshajiangensis gen. et sp. nov., from the Middle Jurassic Zhanghe Formation of Yunnan Province, China. The new taxon is represented by a cranium and the anterior section of the vertebral column including the complete cervical series and the first dorsal vertebra. Yuanmouraptor jinshajiangensis can be diagnosed based on the following autapomorphies: the anterior process of postorbital sheet-shaped and keeping consistent depth; ventral ramus of postorbital bearing a laterally twisted trough running along its lateral surface; ventral surface of axial intercentrum parallel with that of axial centrum; discontinuity of inclination on anterodorsal margin of the third and fourth cervical vertebrae; strongly posteriorly elongated epipophyses of anterior cervical vertebrae; deeply excavated pneumatic foramina on the third cervical vertebra; sheet-shaped and subrectangular neural spines of posterior cervical vertebrae. Phylogenetic analysis recovers Yuanmouraptor as the most basal-branching member within Metriacanthosauridae and provides a new alternative phylogenetic topology of non-coelurosaurian tetanurans.
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| Cranium of Yuanmouraptor jinshajiangensis gen. et sp. nov. (LFGT-ZLJ0115). |
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| Premaxilla and maxilla of Yuanmouraptor jinshajiangensis gen. et sp. nov. (LFGT-ZLJ0115). |
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| Reconstruction of the cranium of Yuanmouraptor jinshajiangensis gen. et sp. nov. (LFGT-ZLJ0115). |
Systematic paleontology
Dinosauria Owen, 1842
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Allosauroidea Currie & Zhao, 1993
Metriacanthosauridae Paul, 1988
Yuanmouraptor gen. nov.
Yuanmouraptor jinshajiangensis gen. et sp. nov.
Etymology—The genus name, ‘Yuanmou’, refers to Yuanmou County where the holotype was collected, and ‘raptor’ is Latin for the robber. The specific name, ‘jinshajiang’ (namely the Jinsha River, the middle region of the Yangtze River) which passes through Yuanmou County and the type locality is located on the north bank of the river.
Holotype—LFGT-ZLJ0115: a partial skeleton consists of a nearly complete skull with mandible and 11 articulated anterior vertebrae including 10 cervical vertebrae and the first dorsal vertebra.
Type Locality and horizon—Xiabanjing Village, Jiangyi Township, Yuanmou County, Chuxiong Yi Autonomous Prefecture, Yunnan Province, China; Zhanghe Formation, early Middle Jurassic, Aalenian/Bajocian (Bureau of Geology and Mineral Resources of Yunnan Province, 1990).
Diagnosis—A medium-sized metriacanthosaurid dinosaur differing from other metriacanthosaurids by the following unique combination of characters (autapomorphies are indicated with an asterisk): an accessory foramen located within antorbital fossa on lacrimal and ventral to pneumatic foramen, similar to Allosaurus; dorsal part of lacrimal bearing a low rugosity, similar to megalosaurids; lack of pneumatic fenestra on lateral surface of jugal, shared with non-tetanurans; the anterior process of postorbital sheet-shaped and its depth keeping consistent*; ventral ramus of postorbital bearing a laterally twisted trough running along its lateral surface*; ventral surface of axial intercentrum parallel with that of axial centrum, shared with Piatnitzkysaurus and non-tetanurans; discontinuity of inclination on anterodorsal margin of the third and fourth cervical vertebrae, similar to that of Dilophosaurus and Baryonyx; flattened peripheral band on anterior articular surface of anterior cervical centra, shared with megalosaurids and some ceratosaurians; strongly posteriorly elongated epipophyses on anterior cervical vertebrae*; strongly ventromedially excavated pneumatic foramen on the third cervical vertebra*; sheet-shaped and subrectangular neural spines of posterior cervical vertebrae*.
Yi Zou, Li Chen, Tao Wang, Guo-Fu Wang, Wei-Gang Zhang, Xiao-Qin Zhang, Zhen-Ji Wang, Xiao-Chun Wu and Hai-Lu You. 2025. A New metriacanthosaurid Theropod Dinosaur from the Middle Jurassic of Yunnan Province, China. PeerJ. 13:e19218. DOI: doi.org/10.7717/peerj.19218
