Scientists have discovered a 246-million-year-old marine reptile fossil, the oldest of its kind found in the Southern Hemisphere, shedding new light on the early evolution of marine mammals.
The largest mass extinction event in the fossil record—known as the “Great Dying”—occurred about 252 million years ago, wiping out about 95% of species on land and in the sea.
What followed was the appearance of new creatures that evolved from those that survived, including reptiles that evolved from living on land to living in the sea.
Sauropterygians were ancient aquatic reptiles that existed for about 180 million years during the Mesozoic Era, 251 to 66 million years ago.
Notosaurs were a type of sauropterygian that lived on Earth during the Triassic period, the first period of the age of dinosaurs, 251 million to 200 million years ago.
However, their early evolution was known only from fossils found in the northern hemisphere, according to the study published in the journal Current Biology on Monday.
Fossils of these animals are commonly found in Europe, as well as southwestern China and the Middle East, with some fragmentary occurrences in Wyoming in the United States and British Columbia in Canada, according to study lead author Benjamin Kear, a paleontologist at Uppsala University. Museum of Evolution in Sweden.
“But it’s completely unexpected to find one on the other side of the Earth,” Kear told CNN on Tuesday.
At the time the notosaurs existed, almost all of Earth’s land masses were included in a supercontinent known as Pangea. This supercontinent was shaped like a horseshoe, and in the middle of it was the Paleo-Tethys Ocean where these animals were thought to have lived, according to Kear.
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 giant global ocean called Panthalassa, which stretched from pole to pole.
“It’s 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 kind of turns everything upside down,” Kear said.
According to a university press release, a single notosaur vertebrae was found in a loose bead along the Balmacaan Stream at the base of Mount Harper in New Zealand in 1978. Many fossils have been found over time and this material is deposited in the Collection National Paleontology of New Zealand, Kear said. The late paleontologist Robert Ewan Fordyce alerted him to the discovery, but the coronavirus pandemic delayed researchers from traveling to see it until last year.
Only after an international team of paleontologists examined the bead and fossils from the surrounding rocks did they discover that it pushed back the fossil record of sauropterygians in the Southern Hemisphere 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, that they basically adapted to life in the sea and … suddenly became global.”
The researchers said the fossil provides the first evidence that early globalization was happening at the same time that these reptiles were growing as oceanic predators and complex marine ecosystems were forming.
The study suggests that these ancient marine reptiles were going around the Earth’s poles, swimming all the way around the supercontinent as a continuous coastal highway, Kear said.
Notosaurs had a slender body, long neck, long limbs and a tail. They would have paddled through the water with their limbs. But over time, later sauropterygians developed better shovels.
Kear, who also works on Svalbard in the Norwegian Arctic, said researchers are planning to look for more fossils around the world in an effort to “trace these stories from pole to pole” and understand how the animals were migrating. around the supercontinent.
“What we’re seeing 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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