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Polar sea reptile 'nothosaur' fossil is the oldest ever discovered

An international team of scientists has uncovered the oldest fossil of a polar sea reptile, called a nothosaur, from the Southern Hemisphere. The nothosaur vertebra, found on New Zealand’s South Island, dates back 246 million years.

This period marks the dawn of the Age of Dinosaurs, during which New Zealand was part of the southern polar coast of the vast Panthalassa super-ocean.

Dawn of sea reptiles

Following a catastrophic mass extinction around 252 million years ago, reptiles began to invade the seas, marking a pivotal evolutionary milestone.

Until now, evidence of this transition had only been found in a few locations, such as Spitsbergen in the Arctic, northwestern North America, and southwestern China.

The discovery of a single vertebra in a stream bed near Mount Harper on New Zealand’s South Island provides new insight into the early presence of sea reptiles in the Southern Hemisphere.

Nothosaurs ruled the ancient seas

Before dinosaurs roamed the land, reptiles like the nothosaurs dominated the seas.

Nothosaurs were part of the sauropterygian group, known for its diverse and long-surviving species, including the long-necked plesiosaurs reminiscent of the Loch Ness Monster.

Illustration of a nothosaur ancient sea reptile. Credit: Johan Egerkrans
Illustration of a nothosaur ancient sea reptile. Credit: Johan Egerkrans

Nothosaurs, growing up to seven meters long, swam with four paddle-like limbs and used their flattened skulls and slender conical teeth to catch fish and squid.

Sea reptiles in the Southern Hemisphere

Discovered during a geological survey in 1978, the nothosaur’s importance remained unrecognized until a collaborative effort by paleontologists from Sweden, Norway, New Zealand, Australia, and East Timor.

Dr. Benjamin Kear from The Museum of Evolution at Uppsala University, lead author of the study, emphasizes the fossil’s significance.

“The nothosaur found in New Zealand is over 40 million years older than the previously oldest known sauropterygian fossils from the Southern Hemisphere,” explains Dr. Kear.

“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.”

Revising theories on Nothosaur migration

Previously, the oldest known nothosaur fossils, dating back around 248 million years, were found in a northern low-latitude belt stretching across the Panthalassa super-ocean.

The origin and distribution of these reptiles have been subjects of debate, with theories suggesting various migration routes.

The discovery of the New Zealand nothosaur challenges 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 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,” Dr. Kear elaborates.

Sea reptile fossils hint at global migrations

The early Age of Dinosaurs was characterized by extreme global warming, which facilitated the thriving of marine reptiles at the South Pole.

This suggests that ancient polar regions were likely routes for their global migrations, similar to the epic trans-oceanic journeys undertaken by whales today.

Nothosaur vertebra fossil. Image credit: Stavros Kundromichalis
Nothosaur vertebra fossil. Image credit: Stavros Kundromichalis

“Undoubtedly, there are more fossil remains of long-extinct sea monsters waiting to be discovered in New Zealand and elsewhere in the Southern Hemisphere,” Dr. Kear concludes.

This remarkable discovery not only provides a new understanding of early sea reptiles in the Southern Hemisphere but also opens the door to further exploration and potential findings of long-extinct marine creatures.

Sea reptiles beyond fossils

Sea reptiles have a rich history that extends beyond this remarkable discovery. These creatures first appeared over 250 million years ago, following the Permian-Triassic extinction event.

They quickly adapted to marine environments, giving rise to diverse groups like ichthyosaurs, plesiosaurs, and mosasaurs. Ichthyosaurs, resembling modern dolphins, dominated the oceans during the early Mesozoic era.

Plesiosaurs, known for their long necks and broad bodies, thrived throughout the Jurassic period. Mosasaurs, massive predators resembling oversized monitor lizards, ruled the seas during the Late Cretaceous period.

Each of these groups showcased unique adaptations, such as streamlined bodies, powerful limbs, and specialized teeth for catching prey. Their fossils have been found worldwide, offering insights into their evolution and migration patterns.

This rich fossil record helps scientists understand the dynamic changes in marine ecosystems over millions of years and the roles these fascinating creatures played in ancient oceans.

The full study was published in the journal Current Biology.


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