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 event in the fossil record—known as the “Great Dying”—occurred about 252 million years ago, wiping out about 95% of land and sea species.
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.
Nothosaurs 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 Monday.
Fossils of these animals are often 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 Kier, a paleontologist at the Uppsala University Museum of Evolution. in Sweden.
“But it’s totally unexpected to find one on the other side of the Earth,” Kier told CNN on Tuesday.
At the time the notosaurs existed, almost all landmasses were included in a single supercontinent known as Pangea. This supercontinent was shaped like a horseshoe, and in the middle was the Paleo-Tethys ocean, where these animals were thought to live, according to Care.
He said the big question is how these animals got from one side of the Earth to the other, since the other side is surrounded by a giant world ocean called Pantalasa, which stretches from pole to pole.
“It’s never been explained, we don’t know what’s going on. “All of a sudden we find the Notosaurus at the South Pole in New Zealand and it’s like turning everything around,” Kerr said.
A single Nothosaurus vertebra was found in a loose thickening along Balmakaan at the foot of Mount Harper in New Zealand in 1978, according to a university press release. Many fossils are constantly being found and this material is deposited in the National Paleontological Collection of New Zealand, Kerr said. The late paleontologist Robert Ewan Fordyce alerted him to the find, but the coronavirus pandemic delayed researchers from traveling to look at it until last year.
It wasn’t until an international team of paleontologists examined the vertebra and fossils from the rocks surrounding it that they discovered it displaced sauropterygian fossils in the Southern Hemisphere by more than 40 million years.
Care 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 basically adapted to life in the sea and … all of a sudden they became global. “
The researchers said the fossil provides the first evidence that early globalization was happening at the same time that these reptiles were rising as ocean predators and complex marine ecosystems were forming.
The study suggests that these ancient marine reptiles circled Earth’s poles, swimming all the way around the supercontinent as a continuous coastal highway, Kerr said.
Nothosaurs had a slender body, long neck, long limbs and tail. They would row through the water with their limbs. But over time, later sauropterygians developed better oars.
Care, who also works in Svalbard in the Norwegian Arctic, said the researchers plan to look for more fossils around the world in an attempt to “trace these stories from pole to pole” and understand how animals migrated around the supercontinent.
“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 have already adapted to life in the sea,” he said. “We’ll see, we’ll keep digging and see what we can find.”
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