Chinese paleontologists have excavated a fossil-rich complex revealing the diverse food chain of an early Jurassic freshwater lake. The findings of thousands of fish, including new species, ancient relatives of sharks and even plesiosaurs, have revealed a colorful fauna that survived after going extinct nearly 200 million years ago.

In the Sichuan depression (basin) in eastern China there are transitional formations from the Triassic (251.9-201.3 million years ago) to the Jurassic (201.3-145 million years ago) periods: Late Triassic Xujiahe, Early Jurassic Zhenzhuchong and others. In these regions, Chinese paleontologists have recently discovered large amounts of fossils characteristic of deep freshwater lakes. The fossil complex was called the Yuzhou (Yuzhou) biota.

In a new article published in the journal Scientific ReportsThe researchers described only the preserved fauna of the Sinemurian phase of the Jurassic period (199.5 (±0.3)-192.9 (±0.3) million years ago). Thousands of fossils provide evidence of one of the oldest food chains from which paleontologists have reconstructed the lake’s complex ecosystem. All things considered, it was preserved after the mass extinction that occurred between geological periods.

The biota is represented by invertebrates (bivalves and gastropods), crustaceans, ray-finned and bivalve fish, extinct hybodonts (close relatives of modern sharks) and pliosaurs (short-necked plesiosaurs). Vegetation (more than 20 species) (ferns, gingko, conifers and others) has also been preserved.

The most numerous class was precisely the ray fins of fish (actinopterygii), paleontologists have recorded several thousand specimens; among them are six new, but as yet undescribed, species. The greatest of these is an individual of the lower class pticolepiformsIt reached a length of 70 centimeters. It turns out that the smallest fish in this biota is also interesting; Experts suggest that the remains of a 13-centimeter-long individual may belong to the Early Jurassic taxon Dorsetichthys, found only in Europe.

Scientists have identified the surviving skeleton of a half-meter-long individual among bivalve fish; The specimen is represented with details of both the skull and the axial skeleton, fins and scales. According to the authors of the article, this is the most complete known fossil of an ancient group. Teeth and dorsal fins remained from the hybodonts, according to which paleontologists determined the maximum length of the fish to be almost a meter. Represented by several vertebrae and skull fragments, the body size of pliosaurus is estimated to have been four times larger. Taken to the landscape Bishanopliosaurus youngi something little known.

The nearly completed femur of a bird-pelvis dinosaur resembles a mansion. The researchers were unable to determine who this belonged to, but it appears to belong to a species close to the co-cursor. This Late Triassic lizard lived in what is now South Africa and was probably a fast runner. However, the dinosaur bone was found there by chance; It looks terrestrial. And the indigenous inhabitants of the ancient reservoir exhibited a complex food chain.

Molluscs and crustaceans can feed on algae and plankton. They were also eaten by jawed fish. They were preyed upon by hybodonts, and at the top of the chain were pliosaurs. Experts discovered the remains of double fish in bromalites, the fossil contents of the stomach and intestines. No one attacked pliosaurs in the freshwater lake studied, so such an environment could be a haven for these lizards. However, since not all samples of the Yuzhou biota have yet been prepared and described, new details could expand the diversity of the ecosystem.