Scientists have discovered a 246-million-year-old fossil of a marine reptile, the oldest of its kind found in the Southern Hemisphere, shedding new light on the early evolution of marine mammals.
The largest mass extinction in the fossil record – known as ‘The Great Dying’ – occurred around 252 million years ago, wiping out around 95% of terrestrial and marine species.
What followed was the emergence of new creatures that evolved from those that survived, including reptiles that evolved from life on land to life at sea.
Sauropterygians were ancient aquatic reptiles that existed for about 180 million years during the Mesozoic Era, 251 to 66 million years ago.
Nothosaurs were a type of Sauropterygian that lived on Earth during the Triassic, the first period of the dinosaur age, 251 million to 200 million years ago.
However, their early evolution was only known from fossils found in the Northern Hemisphere, according to the study published in the journal Current Biology Monday.
Fossils of these animals have been found commonly in Europe, but also in southwestern China and the Middle East, with some patchy occurrences in Wyoming in the United States and British Columbia in Canada, according to lead study author Benjamin Kear, a paleontologist at the University of Uppsala. Museum of Evolution in Sweden.
“But it’s totally unexpected to find one on the other side of the Earth,” Kear told CNN on Tuesday.
At the time when nothosaurs existed, almost all of Earth’s landmasses were included in one supercontinent known as Pangea. This supercontinent was shaped like a horseshoe and at its center was the Paleo-Tethys Ocean, where Kear believed these animals lived.
He said the big question was how these animals got from one side of the Earth to the other, since the other side was surrounded by a gigantic global ocean called Panthalassa, which stretched from pole to pole.
“This has never been explained, we don’t know what’s going on. All of a sudden we find the nothosaur at the South Pole in New Zealand and so it seems like everything has been turned upside down,” Kear said.
According to a university news release, a single nothosaur vertebra was found in 1978 in a loose bollard along the Balmacaan Stream at the foot of Mount Harper in New Zealand. Many fossils are being found all the time and this material has been deposited in New Zealand’s National Palaeontological Collection, Kear said. The late paleontologist Robert Ewan Fordyce alerted him to the find, but the coronavirus pandemic prevented researchers from traveling to look at it until last year.
Only after an international team of paleontologists examined the vertebra and fossils from the rocks around it did they discover that it pushed back the Southern Hemisphere’s sauropterygian fossil record by more than 40 million years.
Kear said the age of the fossil is “really interesting” because it shows that “246 million years ago, which is very close to the dawn of the age of the dinosaurs, they actually adapted to life in the sea and …suddenly went global. ”
The researchers said the fossil provides the first evidence that early globalization occurred at the same time that these reptiles were emerging as oceanic predators and complex marine ecosystems were forming.
The study suggests that these ancient marine reptiles walked around Earth’s poles and swam all the way around the supercontinent as a continuous coastal highway, Kear said.
Nothosaurs had a slender body, a long neck, long limbs and a tail. They would have paddled through the water with their limbs. But over time, later sauropterygians developed better paddles.
Kear, who also works on Svalbard in the Norwegian Arctic, said researchers plan to search around the world for more fossils in an effort to “follow these stories from pole to pole” and understand how the animals around the supercontinent migrated.
“What we’re looking at here is probably a story that goes beyond this super extinction event, goes deeper in time, and we can start to see that these animals were already adapting to life in the sea,” he said. “We’ll see, we’ll keep digging and see what we can find.”
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