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  6. New species of 240-million-year-old marine predator had a built-in “float”

New species of 240-million-year-old marine predator had a built-in “float”

Tyler Stone © Canadian Museum of Nature.

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Brevicaudosaurus jiyangshanensis is a new species of marine reptile described from fossils found in southwest China.

Ottawa, October 28, 2020 - About 240 million years ago, when reptiles ruled the ocean, a small lizard-like predator floated near the bottom of the ocean edges in shallow water, picking off prey with fang-like teeth. A short and flat tail, used for balance, helps identify it as a new species, according to research published in the Journal of Vertebrate Paleontology.

Paleontologists at the Chinese Academy of Scientists and Dr. Xiao-Chun Wu at the Canadian Museum of Nature have analysed two skeletons from a thin layer of limestone in two quarries in southwest China.

They identified the skeletons as nothosaurs. These are Triassic marine reptiles with a small head, fangs, flipper-like limbs, a long neck, and normally an even longer tail, probably used for propulsion. However, in the new species, the tail is short and flat.

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

Xiao-Chun Wu © Canadian Museum of Nature

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The two fossils of the new species found in southwest China. The most complete of the two skeletons was found in the Jiyangshan quarry, giving the specimen its species name.

The new species is named Brevicaudosaurus jiyangshanensis, from the Latin ‘brevi’ for ‘short,’ ‘caudo’ for ‘tail,’ and the Greek ‘sauros’ for ‘lizard.’ The most complete skeleton of the two, just under 60 cm long, was found in Jiyangshan quarry, giving the specimen its species name.

The skeleton gives further clues to its lifestyle. The forelimbs are more strongly developed than the hind limbs, suggesting they played a role in helping the reptile to swim. The bones in the front feet are short compared to other species, limiting the power with which it could pull through the water. Most of its bones, including the vertebrae and ribs, are thick and dense. These characteristics would add to the reptile’s stocky, stout appearance, limiting its ability to swim quickly but increasing its stability underwater.

What the reptile lost in speed, it gained in stability with its thick, high-mass bones acting as ballast. Together with the flat tail, this would have helped the predator to float motionless underwater, requiring little energy to stay horizontal. Neutral buoyancy should also have enabled it to walk on the seabed searching for slow-moving prey. Highly dense ribs may also suggest the reptile had large lungs, which would have increased the time the species could spend under water.

“Nothosaurs were quite large, usually about 3-4 metres long; some up to 5–7 metres. Brevicaudosaurus jiyangshanensis is the smallest so far known. Perhaps this small, slow-swimming marine reptile had to be vigilant for large predators as it floated in the shallows, as well as being a predator itself,” says co-author Dr. Xiao-Chun Wu from the Canadian Museum of Nature.

The study was supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the Canadian Museum of Nature.

Information for media, including images: 

Dan Smythe
Media Relations
Canadian Museum of Nature
613-698-9253 (cell)
dsmythe@nature.ca