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Fossil of what could be the largest marine reptile to ever exist

Paleontologists have announced the discovery of a colossal marine reptile that could be the largest to ever populate Earth's oceans.

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Published in 
 · 18 Apr 2024

The newly identified species, described in a study published in the journal PLOS ONE (, is an ichthyosaur, a group of extinct marine reptiles that somewhat resemble modern dolphins.

Ichthyosaurs inhabited the world's oceans between about 250 million and 90 million years ago. Although their existence coincides with the age of dinosaurs, they are not dinosaurs. Dubbed Ichthyotitan severnensis, this newly described species is estimated to have reached enormous proportions, perhaps measuring 25 meters in length, which is comparable to the size of some blue whales.

However more evidence is needed to definitively determine the size of this prehistoric titan, given that the new species has been described based on just two separate jaws found in the UK.

Fossil of what could be the largest marine reptile to ever exist
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Both fossils represent a type of long, curved bone known as a surangular, found in most land vertebrates, excluding mammals, in the upper part of the lower jaw, just behind the teeth. One of the jaws, more than 2m long, was discovered on a beach in the county of Somerset, south-west England.

The first pieces of the jaw were spotted in May 2020, at a location known as Blue Anchor while searching for fossils. Previously, in 2016 another giant, albeit incomplete, was discovered at a site a few miles along the Somerset coast from Blue Anchor and called Lilstock.

The fact that Blue Anchor and Lilstock are located within the Westbury Mudstone geological formation helped the research team link the two surangular bones found just a few years apart and determine that they represented a new species of ichthyosaur.

Of the two bones, the more recently discovered one is the more complete and better preserved.

Fossil of what could be the largest marine reptile to ever exist
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After first appearing around 250 million years ago, ichthyosaurs had evolved to reach at least 15 meters in length in the space of a few million years. By the end of the Late Triassic period (237 to 201 million years ago), the largest of these marine reptiles had emerged, including I. severnensis, whose fossils date back to about 202 million years ago. But while some species of ichthyosaurs continued to roam the oceans for millions of years, the giant members of this group appear to have become extinct during a mass extinction event that occurred at the boundary between the Triassic and Jurassic periods about 200 million years ago.

At 202 million years old, their fossils just predate a major global extinction event, after which these giants will become extinct. Marine reptiles will never reach such enormous sizes again.

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