New analysis has found that ancient Arctic reptile fossil is the oldest ever found in the Southern Hemisphere

An international team of scientists has identified the oldest fossil of a sea-going reptile in the Southern Hemisphere: a nothosaur vertebra found on New Zealand’s South Island. 246 million years ago, at the dawn of the dinosaur age, New Zealand lay on the south polar coast of a vast superocean called Panthalassa.

Reptiles first invaded the seas after a catastrophic mass extinction that devastated marine ecosystems and paved the way for the dawn of the age of dinosaurs nearly 252 million years ago. Evidence for this evolutionary milestone has only been discovered in a few places around the world: on the Arctic island of Spitsbergen, in northwestern North America and in southwestern China.

Although represented by only a single vertebra excavated from a boulder in a streambed at the foot of Mount Harper on New Zealand’s South Island, this discovery has shed new light on the previously unknown record of early marine reptiles of the Southern Hemisphere .

Reptiles ruled the seas for millions of years before dinosaurs dominated the land. The most diverse and geologically longest-lived group were the sauropterygians, with an evolutionary history of more than 180 million years. The group included the long-necked plesiosaurs, which resembled the popular image of the Loch Ness Monster.

Nothosaurs were distant ancestors of the Plesiosaurs. They could grow up to seven meters in length and swam with four paddle-like limbs. Nothosaurs had flattened skulls with a network of slender cone-shaped teeth that were used to catch fish and squid.

The New Zealand nothosaur was discovered during a geological survey in 1978, but its importance was not fully recognized until paleontologists from Sweden, Norway, New Zealand, Australia and East Timor combined their expertise to examine the vertebrae and other associated fossils and analyze. The article is published in the magazine Current biology.

“The nothosaur found in New Zealand is more than 40 million years older than the previously oldest known sauropterygian fossils from the Southern Hemisphere. We show that these ancient marine reptiles lived in a shallow coastal environment teeming with marine life within what was then the Southern Arctic Circle. ”, explains Dr. Benjamin Kear of the Museum of Evolution at Uppsala University, lead author of the study, explains.

The oldest nothosaur fossils are about 248 million years old and were found along an ancient low-latitude northern belt that extended from the remote northeastern to northwestern margins of the Panthalassa superocean. The origin, spread, and timing of when nothosaurs reached these distant areas are still debated. Some theories suggest that they either migrated along the northern Arctic coasts, or swam through the inland sea, or used currents to cross the Panthalassa superocean.

The new nothosaur fossil from New Zealand has now turned these long-standing hypotheses on their head.

‘Using a time-calibrated evolutionary model of sauropterygian global distributions, we show that nothosaurs originated near the equator and then rapidly spread both north and south, at the same time that complex marine ecosystems were recovering after the cataclysmic mass extinction that marked the beginning. of the age of the dinosaurs,” says Kear.

‘The beginning of the dinosaur age was marked by extreme global warming, which allowed these marine reptiles to thrive in the South Pole. This also suggests that the ancient polar regions were a likely route for their earliest global migrations, much like the epic trans-oceanic journeys that whales undertake today.

“No doubt there are more fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the Southern Hemisphere,” Kear adds.