An article published in the journal “eLife” reports the identification of a new species of armored dinosaurs that lived between 192 and 174 million years ago, at the beginning of the Jurassic period, in today’s China. A team of researchers named it Yuxisaurus kopchicki and assigned it to the group of thyreophorans (Thyreophora), which includes the many armored dinosaurs such as the famous stegosaurs and ankylosaurs. The new species is the first of this group to be described thanks to early Jurassic fossils discovered in Asia. This confirms this group’s quick spread and diversification.
Thyreophorans were herbivorous dinosaurs that appeared at the beginning of the Jurassic period and their main feature was the presence of bony plates and points that offered protection and also means of defense thanks to their tail from the attacks of carnivores. Their diffusion during the Jurassic made them an important part of the fauna until the end of the Cretaceous when they became extinct in the great mass extinction that eliminated them together with the other dinosaurs.
Despite their diffusion, the evolutionary history of thyreophorans still has various parts that are not well reconstructed. For this reason, the relationships between the various species are still under discussion and in recent years a new, deeply revised version has been proposed. The problem is typical in the field of paleontology, the limited availability of fossils dating back to the early Jurassic when this group appeared. For this reason, the identification of the species Yuxisaurus kopchicki may be important in this reconstruction.
A partial skeleton was discovered in the Fengjiahe Formation, in the Yuxi prefecture area of Yunnan province, China. The availability of the bones visible in the scheme of the top image (Courtesy Yao Xihui. All rights reserved) is limited but the researchers who examined those fossils found that the anatomical differences from known thyreophorans and the combination of features were sufficient to assign it to a new genus.
The researchers estimated that the Yuxisaurus kopchicki specimen discovered was about 3 meters long. According to them, it typically walked on all fours but could also move on two legs, a type of locomotion useful for reaching higher leaves and grasping them with its forelimbs.
The anatomical analysis of Yuxisaurus kopchicki shows similarities with Emausaurus ernsti, another species of thyreophoran that lived slightly later in today’s Germany. The relationship between the two species is more or less close depending on which reconstruction of the thyreophoran tree is considered. According to the authors of the new fossils’ analysis, their relationship is close despite their considerable geographical distance.
The researchers hope that the identification of Yuxisaurus kopchicki will help to better understand the evolution of thyreophorans and provide useful information to eliminate at least some doubts regarding the relationships between the various species. Instead, the idea is confirmed that this group of dinosaurs quickly spread and diversified.
Professor Paul Barrett of the Natural History Museum, London, one of the authors of the study, expressed hope that Yuxisaurus kopchicki is the first of many new dinosaurs discovered by his colleagues in Yunnan. In recent decades, many paleontological sites in China are revealing fossils that are very useful in reconstructing the history of various groups of animals, especially dinosaurs. It’s impossible to predict which fossils have been preserved but it’s possible that among them there are also some other thyreophorans.