A nothosaur vertebra found on the South Island of New Zealand has now been identified as the oldest fossil of a polar marine reptile ever found in the Southern Hemisphere. The nothosaur lived 246 million years ago when New Zealand was inside the southern polar circle.
The sensation behind the nothosaur vertebra found in New Zealand had to wait 46 years to be unveiled. It was discovered back in 1978 during a geological survey, but it was only now that an international research team, whose study was published last week in Current Biology, took a closer look at the fossil.
“The nothosaur found in New Zealand is over 40 million years older than the previously oldest known sauropterygian fossils from the Southern Hemisphere. We show that these ancient sea reptiles lived in a shallow coastal environment teeming with marine creatures within what was then the southern polar circle,” Dr. Benjamin Kear, curator of vertebrate paleontology and researcher in paleontology at the Museum of Evolution at Uppsala University and lead author of the study, said in a university press release.
After the most catastrophic mass extinction in the history of the earth around 252 million years ago, which wiped out around 80 percent of species in the ocean, the first reptiles conquered the seas. Evidence of this has so far only been found on Spitsbergen, in north-western North America and in south-western China.
At the time when the nothosaurs lived on earth, with their first appearance in the Middle Triassic, a warm climate prevailed. There were no polar ice caps and the land masses were united in the primordial continent of Pangaea, which was surrounded by a single superocean, Panthalassa.
The oldest fossils of nothosaurs are around 248 million years old and were found along a belt in low northern latitudes. Where exactly they originated, how they spread around the world and when they reached the remote, then warm polar regions is not yet fully understood. It is assumed that they migrated along the northern polar coasts, swam through inland lakes or used currents to cross the Panthalassa superocean.
However, the new findings that the team gained from the nothosaur vertebra call these theories into question.
“Using a time-calibrated evolutionary model of sauropterygian global distributions, we show that nothosaurs originated near the equator, then rapidly spread both northwards and southwards at the same time as complex marine ecosystems became re-established after the cataclysmic mass extinction that marked the beginning of the Age of Dinosaurs,” explained Dr. Kear, adding: “The beginning of the Age of Dinosaurs was characterised 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, much like the epic trans-oceanic journeys undertaken by whales today. Undoubtedly, there are more fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the Southern Hemisphere.”
Julia Hager, Polar Journal AG
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