Description and Classification

Xinjiangchelys was a medium-sized turtle, with the carapace (the upper part of the shell) of some species reaching lengths of around 40 centimeters (about 16 inches). It possessed a relatively low-domed, oval-shaped carapace and a solid, well-developed plastron (the lower part of the shell). The bones of its shell were fully formed, providing good protection. Its skull structure varied somewhat between species but generally showed features typical of early eucryptodiran turtles.

Xinjiangchelys is classified within its own family, Xinjiangchelyidae. It is considered an important early member of the Eucryptodira, a large group that includes most living turtles (the hidden-necked turtles) and their closest extinct relatives. Studying Xinjiangchelys helps paleontologists understand the evolutionary steps that led to modern turtle diversity. Other related genera in the Xinjiangchelyidae family include Annemys and Protoxinjiangchelys, which also contribute to our knowledge of early turtle evolution in Asia.

Distinguishing Features

Xinjiangchelys can be identified by a combination of features, many related to its shell and skull:

• A generally low-domed, broadly oval carapace that is often wider towards the rear.
• The complete absence of mesoplastra, which are paired bones found in the plastron of some more primitive turtles.
• A characteristic pattern of scutes (the keratinous plates covering the bony shell), including a typically broad nuchal scute at the front of the carapace.
• The vertebral scutes (running down the center of the back) are often wider than they are long.
• Specific features of the temporal region of the skull, such as the extent of the emargination (indentation) at the back of the skull, which provided space for jaw muscle attachment.

Paleoenvironment and Diet

Xinjiangchelys inhabited freshwater environments such as lakes, ponds, and slow-moving rivers. The Qigu Formation, where its fossils are commonly found, represents a warm, semi-arid to humid inland basin with extensive fluvio-lacustrine (river and lake) systems during the Middle to Late Jurassic. This ancient ecosystem was rich in life. Xinjiangchelys shared its world with various other aquatic and terrestrial animals, including other types of turtles, crocodylomorphs, fish, and numerous dinosaurs. For example, the giant sauropod dinosaur Mamenchisaurus, the theropod dinosaur Monolophosaurus, and the early ornithischian dinosaur Gongbusaurus roamed the land nearby.

Based on its freshwater habitat and general turtle anatomy, Xinjiangchelys was likely an omnivore. Its diet probably consisted of aquatic plants, algae, invertebrates like snails and insects, and perhaps small fish or carrion. Its beak-like jaws would have been suited for crushing and tearing a variety of food items.

Significance and Ongoing Research

Xinjiangchelys is a significant fossil genus because it provides crucial information about the early evolution, diversification, and paleobiogeography of eucryptodiran turtles. As one of the best-known Jurassic turtles from Asia, its fossils help to fill gaps in our understanding of how turtles adapted and spread across the globe during the Mesozoic Era. The diversity of species within Xinjiangchelys itself suggests a successful radiation of these turtles in the Jurassic freshwater ecosystems of Central Asia.

Ongoing research on Xinjiangchelys and its relatives continues to refine their placement within the turtle family tree (phylogeny). Paleontologists study newly discovered specimens and re-examine existing fossils using modern techniques to learn more about their anatomy, growth, and lifestyle. Understanding the relationships between different species of Xinjiangchelys, as well as their connection to other xinjiangchelyids like Annemys and to later cryptodires, remains an active area of study. These investigations contribute to a broader picture of vertebrate evolution and the history of freshwater ecosystems during the age of dinosaurs.