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HomeTech & SciencesA giant polar reptile once stalked an ancient super-ocean

A giant polar reptile once stalked an ancient super-ocean

An international team of scientists has identified the oldest marine reptile fossil in the southern hemisphere. This fossilized vertebra belonged to a nothosaur, a distant predecessor of the sea dragon-like plesiosaurs. Measuring up to 7 meters long, this predator swam 250 million years ago along the coast of what is now New Zealand, then located at the South Pole. This major discovery reveals the origin and rapid expansion of these reptiles after the Permian-Triassic mass extinction.

Reptiles, kings of the oceans 250 million years ago

Long before dinosaurs dominated the Earth, reptiles ruled the seas. The most diverse and longest surviving are the sauropterygians, whose evolutionary history spans more than 180 million years. Among them, long-necked plesiosaurs resembled the popular image of the Loch Ness monster.

Nothosaurs, ancestors of plesiosaurs, measured about 7 meters long. They swam using four paddle-shaped limbs. Their flattened skulls housed sharp conical teeth, perfect for catching fish and squid.

New Zealand in the heart of the Panthalassa super-ocean

The discovered nothosaur vertebra dates from a time when New Zealand was located on the south polar coast of a vast ocean called Panthalassa. About 250 million years ago, the Great Dying, a devastating mass extinction, disrupted marine ecosystems. The surviving reptiles took the opportunity to conquer the oceans.

Evidence of this evolutionary turning point had already been found in the Arctic, northwest America and southwest China. This New Zealand fossil, one of the most recent from this period, sheds new light on the history of ancient marine reptiles of the southern hemisphere.

The rediscovery of a forgotten fossil

This nothosaur was discovered in 1978 during a geological survey, embedded in a rock at the foot of Mount Harper on the South Island of New Zealand. Its importance has only recently been fully recognized, thanks to the collaboration of paleontologists from Australia, East Timor, Norway, New Zealand and Sweden.

According to Benjamin Kear, co-author of the study, โ€œthe nothosaur found in New Zealand is more than 40 million years older than the previous oldest sauropterygian fossils in the southern hemisphere. ยป The researchers showed that these marine reptiles lived in a shallow coastal environment teeming with sea creatures, within the Southern Polar Circle at the time.

The origin and rapid expansion of nothosaurs

The origin, distribution and timing of the arrival of nothosaurs in these remote regions are still debated among paleontologists. Some theories suggest that they migrated along north polar coasts, swam across inland seas, or used currents to cross the Panthalassa Ocean. This new discovery challenges these assumptions.

Using a time-calibrated evolutionary model of the global distribution of sauropterygians, the study shows that nothosaurs appeared near the equator, then quickly spread north and south, along with marine ecosystems. complexes were recovering after the catastrophic mass extinction marking the start of the age of dinosaurs.

Global warming conducive to their expansion

At the start of the reign of the dinosaurs, Earth was going through a period of extreme global warming. These high temperatures allowed marine reptiles to thrive at the South Pole. The study suggests that ancient polar regions were likely the main route for the first global migration of nothosaurs, similar to the impressive migrations of whales today.

Further research will be needed to confirm this hypothesis, and can only be done by unearthing other remains of these sea dragons. As Benjamin Kear points out, โ€œThere are undoubtedly other sea monster fossils waiting to be discovered in New Zealand and elsewhere in the southern hemisphere. ยป

This fascinating discovery opens a new page in the history of ancient marine reptiles. It testifies to their incredible capacity for adaptation and expansion, which allowed them to dominate the oceans for millions of years. The future fossils that will be unearthed will certainly make it possible to learn even more about these extraordinary animals and their reign over the seas of the past.

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