Oldest ichthyosaur fossil suggests they evolved before the Age of Dinosaurs

Ichthyosaur fossils found in Norway suggest that the marine reptiles may have survived Earth’s greatest mass extinction event 252 million years ago.

This has researchers surprised. The Permian extinction event, 252 million years ago, is also known as the “Great Dying”. It saw an estimated 90 percent of life on Earth go extinct, and ushered in the Triassic period and the emergence of dinosaurs, which would dominate the globe until the next mass extinction event 66 million years ago.

Ichthyosaurs are marine reptiles, often mistakenly thought of as part of the dinosaur family because they lived at the same time and shared the dinosaurs’ characteristic massive size. They resemble dolphins or sharks in body shape, and like dolphins and whales they were air-breathers which would have to surface to take in oxygen.

Both dinosaurs and the marine reptiles evolved sometime after the emergence of the first reptiles roughly 320 million years ago after amphibious vertebrates took their first steps onto land, lost their gills and became terrestrial specialists.

But exactly when reptiles re-invaded the water is not well understood. It was originally thought that ichthyosaurs evolved from land-dwelling ancestors some time after the Permian-Triassic extinction.

The new Norwegian fossils suggest that ichthyosaurs were around millions of years before the dinosaurs.

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Eleven vertebrae and 15 bone fragments of an ancient marine reptile were found on the Norwegian island of Spitsbergen, north of the Arctic circle. Analysis of rock chemistry and microscopic bone structure led palaeontologists to believe the fossils belong to the oldest ichthyopterygian.

This group of eel-like reptiles were water dwellers who evolved into the famous ichthyosaurs which ruled the seas during the Age of Dinosaurs.

Comparing the vertebrae size to other known ichthyopterygians shows that the animal’s body was probably close to three metres in length.

“The vertebrae turned out to be from a highly advanced, fast-growing, probably warm-blooded and fully oceanic ichthyosaur,” says Benjamin Kear from Sweden’s Uppsala University in a New Scientist article.

An earlier-than-expected evolution may help explain how ichthyosaurs got so big so quickly.

In fact, discoveries over recent months suggest that some ichthyosaurs may have been even bigger than the largest animal ever: the blue whale, which routinely reaches over 30 metres in length and over 150 tonnes. But some of the behemoth marine reptiles evolved only a few million years after they supposedly began swimming the oceans.

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Found in a rock layer from only two million years after the Permian mass extinction calls into question the hypothesis that ichthyosaurs evolved after that extinction event.

But, until Permian-aged fossils of ichthyosaur ancestors are found, the jury is still out on when these marine reptiles took the plunge.

The Spitsbergen fossils are described in a paper published in Current Biology.

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