Paleontologists in China have unearthed a relatively complete skull and vertebrae that belonged to a previously unknown metriacanthosaurid theropod dinosaur from the Middle Jurassic period.
Cranium of Yuanmouraptor jinshajiangensis. Image credit: Zou et al., doi: 10.7717/peerj.19218.
Yuanmouraptor jinshajiangensis roamed our planet approximately 170 million years ago (Middle Jurassic).
This dinosaur was a medium-sized member of the Metriacanthosauridae, a clade of carnivorous dinosaurs that lived on the ancient continental mass Laurasia during the Middle Jurassic to the Early Cretaceous.
“Metriacanthosauridae is a family of carnivorous dinosaurs and represents a basal-branching clade within the Allosauroidea,” said Dr. Yi Zou, a paleontologist with the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences and the University of Chinese Academy of Sciences, and colleagues.
“Some researches claim that metriacanthosaurids possess closer relationship with carcharodontosaurids, rendering Metriacanthosauridae a more derived group within Allosauroidea.”
“No matter what position Metriacanthosauridae has within Allosauroidea, members of this clade mainly came from the Middle to Late Jurassic strata of western China, such as Sichuan, Chongqing, Xinjiang, and Yunnan.”
“Apart from those species found in China, metriacanthosaurid theropods were also reported in the Late Jurassic of England, the Late Jurassic of Kyrgyzstan, and the Late Jurassic and Early Cretaceous of Thailand.”
“Recently, scientists reported a probable distribution of this clade in the Tibetan Plateau.”
The fossilized remains of Yuanmouraptor jinshajiangensis were collected from the Zhanghe Formation in Yunnan province, China.
“The specimen includes a relatively complete skull and the first 11 vertebrae including 10 cervical vertebrae and the anterior-most dorsal vertebra,” the researchers said.
“The preserved skull is measured 53.9 cm in anteroposterior length, and the reconstruction of the skull measures 60.1 cm in anteroposterior length.”
The team’s phylogenetic analysis places the new species at a basal-branching position within Metriancanthosauridae.
“Yuanmouraptor jinshajiangensis presents the most complete cranium among basal-branching tetanurans reported in Middle Jurassic China, and provides valuable anatomic information concerning the unusual combination of plesiomorphies and synapomorphies of cranium and cervical vertebrae in Metriacanthosauridae,” the scientists said.
“In addition, our phylogenetic analysis recovered the phylogenetic position of Piatnitzkysauridae being the sister group to Avetheropoda instead of being within Megalosauroidea.”
“Three major branches within Tetanurae are recovered by our phylogenetic analysis with support of the monophyletic Avetheropoda (Allosauroidea + Coelurosauria) instead of the monophyletic Carnosauria (Megalosauroidea + Allosauroidea).”
“Due to the lack of consensus upon the phylogenetic relationship within basal-branching tetanurans over past decades and many relatively fragmentary materials within Tetanurae, more accuracy in character coding and new findings of early members of this clade are needed to untangle the interrelationship of basal members of the group in the future.”
The discovery of Yuanmouraptor jinshajiangensis is reported in a paper published online in the journal PeerJ.
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Y. Zou et al. 2025. A new metriacanthosaurid theropod dinosaur from the Middle Jurassic of Yunnan Province, China. PeerJ 13: e19218; doi: 10.7717/peerj.19218
