Researchers have discovered the oldest known remains of a giant ancient oceanic reptile, known as an ichthyosaur, on a remote Arctic island, offering new evidence of how the creature may have evolved. 

The fossil was found on Spitsbergen, a Norwegian island, along the coast of a deep fjord, the Swedish and Norweigian research team said in a paper published Monday in the journal Current Biology. Previously, the oldest known such fossil was a 248-million-year-old specimen found in China. 

Ichthyosaurs first appeared around 250 million years ago, researchers said, but went extinct around 90 million years ago. Previously, scientists believed that the first ichthyosaurs would have been primitive creatures that were similar to land-living ancestors. Instead, the researchers found that the fossil was a more advanced aquatic predator, which indicates previous theories may have been wrong about the reptile's origins. 

The study proposes that the reptiles likely evolved before a mass extinction event known as the end-Permian mass extinction, which occurred about 251 million years ago and killed about 90% of species existing on Earth at the time. Ichthyosaurs became a dominant predator after the event. The fossil found was from about 2 million years after the mass extinction. 

"The implications of this discovery are manifold, but most importantly indicate that the long-anticipated transitional ichthyosaur ancestor must have appeared much earlier than previously suspected," said lead researcher Benjamin Kear, curator of vertebrate palaeontology at Uppsala University's Museum of Evolution in Sweden, Reuters reported. 

Features of the fossils show that the creatures were "advanced aquatic tetrapods" that "must have rapidly adapted as oceanic apex predators," the study said. 

The fossil found in Norway was about 10 feet long, researchers said, with advanced vertebrae. It was found amid other fossils, including those of fish, sharks and amphibians. 

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• Fossil

Kerry Breen

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.