Ancient marine predator could float motionless in the water

Scientists have discovered an ancient marine reptile that used a flat tail and a buoyant build to float motionless in the water, where it could sneak attack unsuspecting prey with fang-like teeth. The reptile species, which is now known as Brevicaudosaurus jiyangshanensis, lived about 240 million years ago during the Triassic period when reptiles dominated the ocean.

A team of paleontologists led by the Chinese Academy of Sciences examined two skeletons recovered from a thin layer of limestone in southwest China. The specimens were identified as nothosaurs – marine reptiles with a small head, long neck, and flipper-like limbs. These reptiles typically had long tails, but B. jiyangshanensis stood out as an exception. 

“Our analysis of two well-preserved skeletons reveals a reptile with a broad, pachyostotic body (denser boned) and a very short, flattened tail. A long tail can be used to flick through the water, generating thrust, but the new species we’ve identified was probably better suited to hanging out near the bottom in shallow sea, using its short, flattened tail for balance, like an underwater float, allowing it to preserve energy while searching for prey,” said Dr. Qing-Hua Shang.

The most complete skeleton, which was found in Jiyangshan quarry, is just under 60 centimeters long. The forelimbs were found to be better developed than the hind limbs, indicating that they played a role in helping the reptile swim. However, the bones in the animal’s front feet were rather short compared to other marine reptiles, which would have limited the power that B. jiyangshanensis had to pull through the water. 

According to the researchers, what this reptile lacked in speed was gained in balance. B. jiyangshanensis had thick bones that would have provided stability.

In addition, greater bone density may have made the animals neutrally buoyant in shallow water. Combined with a flat tail, this buoyancy would have helped the lizard-like predator to float motionless underwater while using up very little energy.

There is also evidence that B. jiyangshanensis had large lungs, which would have increased the time it could spend underwater.

“Perhaps this small, slow-swimming marine reptile had to be vigilante for large predators as it floated in the shallows, as well as being a predator itself,” said study co-author Dr. Xiao-Chun Wu.

The study is published in the Journal of Vertebrate Palaeontology.

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By Chrissy Sexton, Earth.com Staff Writer