Ancient “fish lizards” swam around in Earth’s oceans 250 million years ago, long before scientists thought they first emerged, a new study finds.
Researchers in 2014 discovered the fossilized remains of an ichthyosaur on Spitsbergen, a remote Arctic island in Norway’s Svalbard archipelago. Ichthyosaurs are an extinct, fish-like lizard whose body shape resembled that of modern dolphins and toothed whales. The remains, which consist of 11 caudal vertebrae, were trapped in a limestone boulder that dated to the early Triassic period, making the fossils the oldest remains of an ichthyosaur ever discovered and the oldest evidence of marine reptiles.
Scientists previously assumed that ichthyosaurs, along with all other marine reptiles, arose after the Permian mass extinction, also known as the “Great Die,” which occurred about 251.9 million years ago and wiped out about 90% of all life on Earth at the time. Until now, the oldest known fossils of marine reptiles belonged to smaller and less aquatic groups and dated to 249 million years ago, suggesting that marine reptiles may have emerged soon after the destructive event.
But in a new study, published March 13 in the journal Current Biology (opens in new tab)researchers argue that the size and composition of the bones of the ichthyosaur are evidence that the giant ocean predators may have surfaced before the Permian extinction event.
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It is believed that icthyosaurs and other marine reptiles descended from terrestrial reptiles that slowly transitioned into the water to fill an ecological niche left open by the disappearance of oceanic predators. As a result, the first marine reptile species were not perfectly suited to an aquatic lifestyle and likely had dense bones, less streamlined bodies, and did not grow large.
In April 2022, researchers announced the discovery of a tooth from one of the largest ichthyosaurs to ever swim in Earth’s oceans that was probably bigger than the current record holder Shastasaurus sikanniensis, which was 21 meters long.
The vertebrae of the newly exposed ichthyosaurs are the same size as those of later ichthyosaurs, which grew to about 3 meters in length. The bones also have a spongy texture that appears to be well adapted to aquatic life. The team therefore suspects that the lineage of the ichthyosaurs likely arose before the end-Permian mass extinction, as they were unlikely to have evolved these advanced traits in the less than 2 million years after the cataclysmic event occurred. .
The results could force paleontologists to rethink what they thought they knew about the Permian mass extinction event.
“It now appears that at least some groups predate this milestone interval,” the researchers wrote in a rack (opens in new tab). Fossils of other ancient ichthyosaur ancestors and other dinosaur-era reptiles may also be waiting to be found elsewhere in the world, she added.