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Did a Swimming Reptile Predate the Dinosaurs?

Giant reptiles took to the land and sea during the Mesozoic era and dominated the other life. Now the title for earliest and oldest species is up for contention.

By Matt Hrodey
Mar 15, 2023 4:00 PMMar 20, 2023 5:00 PM
Earliest ichthyosaur
Reconstruction of the earliest ichthyosaur. (Credit: Esther van Hulsen)


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Some 250 million years ago, ocean water covered what is now called Flowerdalen (“Flower’s valley”) in modern-day Norway. Life in these waters was different than it had been just 252 million years ago, when the End-Permian Mass Extinction had eliminated 90 percent of marine species from the planet. What remained were plucky opportunists, including a type of sea-dwelling reptile called an ichthyosaur, which had evolved flippers from land-dwelling feet.

When they died, their remains attracted sediments that over millions of years formed limestone boulders like time capsules that now rest among eroded mudstone in Flower’s valley. These Norwegian “concretions” have preserved the bones of early marine fauna, including the adaptable ichthyosaur, for future millenia.

Now, a new ichthyosaur discovery from the valley has broad implications for the history of this time and the dinosaurs.

Read More: The Permian Extinction: Life on Earth Nearly Disappeared During the ‘Great Dying’

An Unexpected Find

In 2014, scientists moved a large number of the concretions to the Natural History Museum at the University of Oslo, including a number considered to be too old to contain ichthyosaur remains. But subsequent research found that they did and dated the bones to 250 million years ago, long before (1.2 million years) the researchers previously thought the reptiles had migrated to the sea. What’s more, the older specimen appeared to be well-evolved, with a light, spongy bone structure well-suited to life underwater.

From analyzing the vertebrae and other pieces, the Swedish and Norwegian researchers concluded that the reptile had roamed in a pelagic fashion, away from the sea bottom and shore, and also possessed a high-powered metabolism. Such traits are common in water-dwelling tetrapods (having four legs) but remarkable in such an old reptile. How had the ichthyosaur acquired them so quickly?

The study suggests that the new species predated the End-Permian Mass Extinction and thus the Mesozoic era, challenging the idea that “major reptile lineages” first emerged during the latter, the Age of Dinosaurs.

In other words, the first major reptile may have been an ichthyosaur, a creature that resembled a full-bodied dolphin and only measured about three meters (according to one estimate) in length. Early ichthyosaurs sometimes reached only a meter long, though they later grew to resemble giant fish millions of years later.

Origin Story

If ichthyosaurs predated the End-Permian Mass Extinction, when and where did they originate? The study lacks specifics and admits to the need for more discoveries to be made “in even older rocks on Spitsbergen [in Norway] and elsewhere in the world.”

For sure, the study disagrees with what it calls textbook accounts of reptiles wandering down to the shore after extinction, “to take advantage of marine predator niches that were left vacant” by the mass extinction. By the researchers' estimation, the reptiles didn't have to walk down; they were already there.

Scientists have found ichthyosaur fossils all around the world, in Thailand, Japan, Canada and China, where continental drift left them to be found. Until recently, the oldest on record came from Nevada, which dated to about 249 million years ago and showed the same spongy bone structure — a key adaptation. As one study found, these reptiles evolved rapidly during their first few million years of aquatic life and then more slowly.

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