Prehistoric sea monster from the UK among the largest animals to have ever lived

Victoria Woollaston April 10, 2018

The seas off the south coast of the UK were once home to one of the largest animals to have ever lived, according to a group of palaeontologists.

Prehistoric sea monster from the UK among the largest animals to have ever lived

Bone fragments, found by fossil collector and researcher Paul de la Salle, were discovered on the beach at Lilstock, Somerset in May 2016 and, when placed together, measure around one metre in length. Analysis has since established that these fragments belong to a giant ichthyosaur, a prehistoric aquatic reptile that lived some 205 million years ago, and experts have estimated the length of the animal’s body to have been up to 26 metres.

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Ichthyosaurs were a fundamental part of Mesozoic marine ecosystems from the Early to the Late Triassic, between 235 and 200 million years ago, until their extinction in the early Late Cretaceous. The largest ichthyosaurs of the Late Triassic were the shastasaurids, which measured anywhere from around six metres, up to the length of Shonisaurus sikanniensis, believed to have measured 21 metres in length.

The isolated jaw fragment of the giant ichthyosaur from the UK, which estimates suggest was even larger than S. sikanniensis, may represent the largest of this genera and would make it as large, or larger, than its Late Triassic dinosaurs contemporaries. To put this into perspective, the largest ichthyosaur previously found in the UK was estimated to measure about 15 metres. While modern-day blue whales measure an average of 25 metres in length, although have been known to grow to a staggering 30 metres.

“Initially, the bone just looked like a piece of rock but, after recognising a groove and bone structure, I thought it might be part of a jaw from an ichthyosaur and immediately contacted ichthyosaur experts,” said de la Salle. In particular, he approahed Dean Lomax from the University of Manchester and Professor Judy Massare for SUNY College at Brockport in New York.

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Bone fragments (pictured), found by fossil collector and researcher Paul de la Salle, were discovered on the beach at Lilstock, Somerset in May 2016

Lomax and Massare identified the specimen as a “large, robust, but incomplete” bone, called a surangular, from the lower jaw of a giant ichthyosaur. The bone is 96cm long and would have made up only a portion of the entire skull. Relatively few surangulars from the largest Triassic ichthyosaurs have been found, and the team said three-dimensional preservation of isolated ones are rare. To estimate the creature’s size, the researchers compared it with several ichthyosaurs bones, and the remains of the previously identified S. sikanniensis.

“As the specimen is represented only by a large piece of jaw, it is difficult to provide a size estimate, but by using a simple scaling factor and comparing the same bone in S. sikanniensis, the Lilstock specimen is about 25% larger,” said Lomax. “Other comparisons suggest the Lilstock ichthyosaur was at least 20-25 metres. Of course, such estimates are not entirely realistic because of differences between species. Nonetheless, simple scaling is commonly used to estimate size, especially when comparative material is scarce.”

The new study is open access and has been published today in the scientific journal, PLOS ONE.

Images: PLOS ONE/Nobumichi Tamura