Illustration of a washed-up Ichthyotitan severnensis carcass on the beach

The fossil jawbone of an ichthyosaur, which may have been around 25 metres long, has been found in Somerset. © Sergey Krasovskiy

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Giant marine reptile found in the UK could be the largest ever discovered

The fossil jawbone of an ichthyosaur, which may belong to the largest marine reptile ever discovered, has been found in southwest England.

This giant of the oceans is estimated to have reached around 25 metres in length, which is about the size of a modern-day blue whale.

The UK is certainly no stranger to unearthing the fossils of ancient marine reptiles, but a recent discovery may be a new record-breaker.

In 2020, father and daughter Justin and Ruby Reynolds found parts of a huge fossil jawbone measuring more than two metres long on a beach at Blue Anchor in Somerset. The pair were searching for fossils when Ruby, aged 11 at the time, found a large chunk of bone.

Realising the significance of their find, they contacted University of Manchester palaeontologist Dr Dean Lomax, who recognised its significance to a similar, less well-preserved jawbone that was also discovered in Somerset by seasoned fossil collector Paul de la Salle in May 2016.

Analysis of the two specimens confirmed they were from the same species of gigantic ichthyosaur, which may have reached around 25 metres in length. The species has now been named Ichthyotitan severnensis, meaning “giant fish lizard of the Severn.”

Further examination of the bone structure preserved in the more recent Blue Anchor fossils also revealed that this individual was still growing, so questions remain as to just how large these giants of the sea could grow.

Justin, Ruby and Paul were included as co-authors in a study describing the new species, which was published in the journal PLOS One. The fossils will soon go on display at the Bristol Museum and Art Gallery.

Dr Marc Jones, Curator of Fossil Reptiles at the Natural History Museum, says, “We knew that there were giant ichthyosaurs in the Triassic, but this find hints that they were possibly even larger than we thought, and perhaps promises that we will find more of the skeleton in the future.”

Dr Dean Lomax, Ruby Reynolds, Justin Reynolds and Paul de la Salle standing behind a table with the fossil jawbones

Father and daughter Justin and Ruby Reynolds (centre) found parts of the Jawbone while fossil hunting. © Dr Dean Lomax

When did giant ichthyosaurs roam the seas?

Ichthyosaurs are a group of marine reptiles which emerged around 250 million years ago during the Early Triassic Period. While dinosaurs roamed on land, ichthyosaurs became one of the ocean’s top predators.

Although today the award for ocean giants firmly belongs to marine mammals, the earliest ocean giants were reptiles. Ichthyosaurs were the first tetrapods, or four-limbed vertebrates, to reach truly gigantic sizes.

They also appear to have evolved very rapidly, with individuals that reached up to 17 metres long emerging just a few million years after the group first appeared in the fossil record. By the Late Triassic, the largest known ichthyosaurs, belonging to the family Shastasauridae, had evolved.

Dr Dean Lomax, says, “I was amazed by the find. In 2018, my team – including Paul de la Salle – studied and described Paul’s giant jawbone and we had hoped that one day another would come to light. This new specimen is more complete, better preserved, and shows that we now have two of these giant [jaw] bones, called a surangular, that have a unique shape and structure. I became very excited, to say the least.”

“This research has been ongoing for almost eight years. It is quite remarkable to think that gigantic, blue whale-sized ichthyosaurs were swimming in the oceans around what was the UK during the Triassic Period. These jawbones provide tantalising evidence that perhaps one day a complete skull or skeleton of one of these giants might be found. You never know.”

Illustration of a giant pair of swimming Ichthyotitan severnensis.

Giant ichthyosaurs roamed the oceans during the Late Jurassic. © Gabriel Ugueto

What happened to the giant ichthyosaurs?

The more recent Ichthyotitan fossils from Blue Anchor date to around 202 million years ago. This was during the end of the Triassic Period in a time known as the Rhaetian, which means this individual was alive during the final chapters of the giant ichthyosaur’s reign.

Around 201.3 million years ago, a mass extinction event marked the boundary between the Triassic and Jurassic Periods. The cause of this extinction is still not fully understood. But massive volcanic activity in what is now the Atlantic Ocean released so much carbon dioxide and sulphur dioxide that it is believed to have led to a dramatic shift in the climate.

As sea levels began to rise and the oceans became more acidic, severe extinctions occurred throughout the marine environment. Among them were the giant ichthyosaur family Shastasauridae.

Although Ichthyotitan was not the world’s first giant ichthyosaur to evolved, the remains appear about 13 million years after other discoveries of their massive relatives. This includes Shonisaurus sikanniensis from British Columbia, Canada, and Himalayasaurus tibetensis from Tibet, governed by China.

Other, smaller species of ichthyosaur survived beyond the Triassic-Jurassic boundary and gave rise to new radiations of ichthyosaurs all the way into the Cretaceous before their extinction 65 million years ago. However, these ancient reptiles never seem to have reached such large sizes again.