New analysis determines ancient polar marine reptile fossil is oldest ever found in the Southern Hemisphere.

An international team of scientists has identified the oldest fossil of a marine reptile in the Southern Hemisphere: a nothosaur vertebra found on the South Island of New Zealand. 246 million years ago, at the start of the age of dinosaurs, New Zealand was located on the south polar coast of a vast super-ocean 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 of this evolutionary stage has only been found in a few places in the world: on the Arctic island of Spitsbergen, in northwest North America, and in southwest China.

Although represented by a single vertebra extracted from a rock in a stream bed at the foot of Mount Harper on New Zealand’s South Island, the discovery has shed new light on the previously unknown record of the first marine reptiles of the southern hemisphere. .

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

Nothosaurs were distant predecessors of plesiosaurs. They could measure up to seven meters in length and swim using four paddle-like limbs. Nothosaurs had a flattened skull with a network of fine conical teeth that were used for catching fish and squid.

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

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

The oldest nothosaur fossils are approximately 248 million years old and were discovered along an ancient low-latitude northern belt that extended from the far northeast to northwest margins of the Panthalassa super-ocean . The origin, distribution, and when nothosaurs reached these distant regions are still debated. Some theories suggest that they either migrated along the northern polar coasts, swam inland sea lanes, or used currents to cross the Panthalassa super-ocean.

New Zealand’s new nothosaur fossil has upended these long-held assumptions.

“Using a time-calibrated evolutionary model of global sauropterygian distributions, we show that nothosaurs originated near the equator, then rapidly spread north and south at the same time as complex marine ecosystems reestablished after the cataclysmic mass extinction that ushered in the age of dinosaurs,” Kear explains.

“The early age of dinosaurs was characterized by extreme global warming, which allowed these marine reptiles to thrive at the South Pole. It also suggests that the ancient polar regions were a likely route for their first global migrations, a much like the epic trans-oceanic voyages undertaken by whales today.

“There is no doubt that there are other fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the southern hemisphere,” adds Kear.