Paleontologists in China have made an exciting discovery with the unearthing of a new theropod dinosaur from the Middle Jurassic period, around 170 million years ago. The species, named Yuanmouraptor jinshajiangensis, belongs to the Metriacanthosauridae family and was found in the Zhanghe Formation in Yunnan Province, China. The findings detailed in the study published in PeerJ unveil a medium-sized carnivorous dinosaur with a remarkably complete skull and several vertebrae, providing crucial insights into the evolutionary history of theropods.
The Importance of the Yuanmouraptor jinshajiangensis Discovery
The newly discovered species, Yuanmouraptor jinshajiangensis, represents a basal-branching theropod from the Metriacanthosauridae family, a clade of carnivorous dinosaurs that lived during the Middle Jurassic to the Early Cretaceous. This clade primarily existed on the ancient landmass of Laurasia, which included regions like Sichuan, Chongqing, Xinjiang, and Yunnan in China. However, metriacanthosaurids have also been found outside of China, with fossil evidence from the Late Jurassic in England, Kyrgyzstan, and Thailand.
The new species’ discovery is vital because it provides the most complete cranium of a basal-branching theropod found in Middle Jurassic China. The skull of Yuanmouraptor jinshajiangensis measures 53.9 cm in anteroposterior length, with the reconstructed length reaching 60.1 cm. This is a significant find, as the cranium is well-preserved and includes vital anatomical features that help to understand the evolutionary relationships within the Metriacanthosauridae clade.
“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. “Some researches claim that metriacanthosaurids possess a closer relationship with carcharodontosaurids, rendering Metriacanthosauridae a more derived group within Allosauroidea.”
Evolutionary Insights: Phylogenetic Analysis of Yuanmouraptor jinshajiangensis
The team of researchers performed a phylogenetic analysis on the fossilized remains of Yuanmouraptor jinshajiangensis, which confirmed that it holds a basal-branching position within the Metriacanthosauridae family. This position is crucial in understanding the evolutionary tree of theropods, as it helps scientists establish the relative relationships between different groups of dinosaurs within the Allosauroidea superfamily.
The study suggests that while the Metriacanthosauridae family has generally been placed within the Allosauroidea clade, there is still debate about its exact relationship with other theropods. Some researchers believe that metriacanthosaurids are more closely related to the Carcharodontosauridae, a family of large predatory dinosaurs that lived in the Late Jurassic and Early Cretaceous periods. However, regardless of its exact placement, the Metriacanthosauridae family is primarily known from the Middle to Late Jurassic periods in western China, with significant finds in regions such as Sichuan, Chongqing, Xinjiang, and Yunnan.
As Dr. Zou noted, “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.”
A Rich Fossil Record
The Zhanghe Formation in Yunnan Province, where the fossils of Yuanmouraptor jinshajiangensis were discovered, is known for its rich Jurassic fossil record. This area has yielded numerous fossils from a variety of theropods, contributing greatly to our understanding of the ancient fauna that inhabited Laurasia millions of years ago. The fossilized remains of Yuanmouraptor jinshajiangensis consist of a relatively complete skull and vertebrae, including the first 11 vertebrae, which encompass 10 cervical vertebrae and the anterior-most dorsal vertebra.
“The specimen includes a relatively complete skull and the first 11 vertebrae, including 10 cervical vertebrae and the anterior-most dorsal vertebra,” the researchers stated. These remains, in combination with other fossil evidence from the area, provide valuable information regarding the anatomical structure of this theropod and its place in the Metriacanthosauridae lineage.
The Role of Yuanmouraptor jinshajiangensis in Theropod Evolution
The discovery of Yuanmouraptor jinshajiangensis is important not just for its completeness, but for the insights it offers into theropod evolution. This dinosaur’s skull and vertebrae demonstrate a unique combination of plesiomorphies (primitive traits) and synapomorphies (shared derived traits) that help clarify the evolutionary path of basal-branching tetanurans. These anatomical features are crucial for understanding the relationship between early theropods and their later relatives.
The study’s phylogenetic analysis supports the idea that Yuanmouraptor jinshajiangensis represents a crucial piece of the puzzle when it comes to untangling the interrelationships of basal theropod groups. As the researchers noted, “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.”
