Researchers have identified what may be the largest known marine reptile after an 11-year-old found fossilised jaw bones on a beach in Somerset, UK.

The new species of enormous ichthyosaur, a type of prehistoric marine reptile, is likely to have been around 25m long – that’s slightly longer than a tennis court. Palaeontologists say it would lived alongside dinosaurs, around 202 million years ago.

A eight-year series of fossil finds, described as a multimillion-year-old jigsaw, led to the ichthyosaur's identification.

Father and daughter, Justin and Ruby Reynolds, then aged 11, from Devon, found pieces of a second jawbone in May 2020, while searching for fossils on the beach.

Realising they had discovered something significant, they contacted leading ichthyosaur expert, Dr Dean Lomax, a paleontologist at the University of Manchester. Lomax then contacted Paul de la Salle, a seasoned fossil collector who had found the first giant jawbone in May 2016, further along the coast.

Lomax said, “I was amazed by the find. In 2018, my team 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 bones - called a surangular - that have a unique shape and structure. I became very excited, to say the least.”

Justin and Ruby, together with the researchers and several family members, visited the site to hunt for more pieces of the rare discovery. Over time, they found additional pieces of the same jaw which fit together perfectly.

Justin said: “When Ruby and I found the first two pieces we were very excited as we realised that this was something important and unusual. When I found the back part of the jaw, I was thrilled because that is one of the defining parts of Paul's earlier discovery.”

The last piece of bone was recovered in October 2022. The research team have called the new species Ichthyotitan severnensis, meaning “giant fish lizard of the Severn”.

The bones date to the end of the Triassic period in a time known as the Rhaetian. During this time, the gigantic ichthyosaurs swam the seas while the dinosaurs walked on land.

It was the creatures' final chapter, however - the story told in the rocks above the fossils record a cataclysm known as the Late Triassic global mass extinction event. After this time, giant ichthyosaurs go extinct. Today, these bones represent the very last of their kind.

Lomax said, “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.

“I was highly impressed that Ruby and Justin correctly identified the discovery as another enormous jawbone from an ichthyosaur. I asked them whether they would like to join my team to study and describe this fossil, including naming it. They jumped at the chance.

"For Ruby, especially, she is now a published scientist who not only found but also helped to name a type of gigantic prehistoric reptile.”

Ruby said: “It was so cool to discover part of this gigantic ichthyosaur. I am very proud to have played a part in a scientific discovery like this.”

The team's discoveries are due to go on display at the Bristol Museum and Art Gallery.