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

An international team of scientists has identified the oldest marine reptile fossil from the Southern Hemisphere – a Nothosaurus vertebra found on New Zealand’s South Island. 246 million years ago, at the beginning of the age of the dinosaurs, New Zealand was located on the south polar coast of a huge 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 been discovered in only a few places around the world: the Arctic island of Svalbard, northwestern North America, and southwestern China.

Although represented by only a single vertebra excavated from a boulder in a stream bed at the foot of Mount Harper in the South Island of New Zealand, the discovery shed new light on a previously unknown record of early marine reptiles from the southern hemisphere. .

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

Nothosaurs were the distant ancestors of Plesiosaurs. They could grow up to seven meters long and swam using four paddle-like limbs. Nothosaurs had flattened skulls with a mesh of slender, cone-shaped teeth that were used to hunt fish and squid.

The New Zealand nothosaur was discovered during a geological survey in 1978, but its significance was not fully recognized until paleontologists from Sweden, Norway, New Zealand, Australia, and East Timor joined their expertise to examine and analyze the vertebra and other associated fossils. The work is published in a journal Contemporary Biology.

“A notosaur found in New Zealand is more than 40 million years older than the previously 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 Southern Arctic Circle.” “explains Dr. Benjamin Kear of The Museum of Evolution at Uppsala University, lead author of the study.

The oldest nothosaur fossils are about 248 million years old and were found along an ancient low-latitude northern belt that stretched from the far northeast to northwest edge of the Panthalassa superocean. The origin, distribution, and timing of when nothosaurs reached these remote areas are still debated. Some theories suggest that they either migrated along the northern polar coasts, or sailed through inland seas, or used currents to cross the Panthalassa superocean.

A new nothosaur fossil from New Zealand has now disproved these long-standing hypotheses.

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

“The beginning of the age of dinosaurs was characterized by extreme global warming, which allowed these marine reptiles to thrive at the South Pole. This also suggests that the ancient polar regions were a likely route for their earliest global migrations, similar to the epic trans-oceanic journeys made by whales today.

“There are undoubtedly more fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the southern hemisphere,” adds Kear.