It may be difficult to imagine, but the county of Somerset in south-west England was once home to what may have been the largest marine reptiles that ever lived, my team's new study reveals.
Author
Dean Lomax
1851 Research Fellow, University of Bristol & Honorary Research Fellow, University of Manchester, University of Manchester
A strange and enormous jawbone was discovered on the English coastline eight years ago, but my team was hesitant to identify it as a new species until more specimens came to light. Now, with the discovery of a second giant jawbone several years later, we have named a new species of ichthyosaur, an ancient marine reptile.
In 2016, prolific fossil hunter Paul de la Salle, unearthed a giant jawbone on the beach at Lilstock in Somerset. It was an incomplete bone from the back of the animal's lower jaw. My team, including De la Salle, studied this discovery and published our findings in 2018 in the journal PLOS One.
His find was important because it was recovered from roughly 202 million-year-old rocks, was very large (1 metre long but incomplete), and clearly belonged to a new species of giant ichthyosaur. The jawbone (called a surangular) had an unusual shape and structure. But we refrained from giving the discovery a name, in the hope that more fossil remains would come along in the future.
Enter a second, more complete and better-preserved specimen, this time representing a right surangular from another individual.
This latest find was made just six miles along the coast at Blue Anchor in 2020. It was found by fossil-hunting father and daughter Justin and Ruby Reynolds (Ruby was then 11). They contacted me almost immediately upon finding it. Over the next few years, along with De la Salle and several of our family members, we collected more fossil fragments, with the last piece found in October 2022.
As we began to piece together different sections of the same jawbone, we estimated that the entire bone would have been just over 2 metres long. The preservation and fine detail provided new information that also helped us to better reinterpret De la Salle's original bone.
Now, we had two specimens with the same unique features and collected from the same geologic timezone. And the fact these two bones appeared roughly 13 million years after the latest-dated giant ichthyosaurs with a scientific name, including Shonisaurus sikanniensis from British Columbia, Canada, and Himalayasaurus tibetensis from Tibet, China, provided support for our identification of a new species.
We therefore erected a new genus (taxonomic rank) and species of giant ichthyosaur that we called Ichthyotitan severnensis, meaning "giant fish lizard of the Severn".
Blue whale-sized giants
With just two giant jawbones, it is impossible to say for sure how large Ichthyotitan really was. However, we know that both specimens are about 25% larger than the same bone in the giant Shonisaurus sikanniensis, an earlier ichthyosaur collected from British Columbia that has an estimated body length of 21 metres.
Using a basic formula called a simple scaling factor, we can estimate that our ichthyosaur was up to 26 metres long, about the size of a blue whale. Comparisons with the same bone in other ichthyosaurs suggests that Ichthyotitan was between 20 and 26 metres in length.
We have to be careful with such estimations due to differences among species, such as those with long or short snouts. However, simple scaling is a common way of estimating size in palaeontology, especially when dealing with fossil fragments. So, based on the information we have available right now, Ichthyotitan severnensis is probably the largest marine reptile formally identified by scientists.
At 202 million years old, the fossils narrowly predate a global extinction event that eradicated these giants - and marine reptiles would never reach such a size again. We think they belonged to a family of ichthyosaurs called Shastasauridae, which vanished during the end-Triassic mass extinction event. The cause is a source of debate among scientists, but may have been triggered by a sudden release of large amounts of carbon dioxide.
As part of our research, we also looked at the bone histology (its microscopic anatomy). Marcello Perillo from the University of Bonn led on this side of the work. Thin sections of the bones revealed the same microscopic features found in similar giant ichthyosaurian specimens. The research also revealed that this giant had yet to reach full maturity and was still growing at the time of death.
Anyone can make a contribution
When I received the initial email from the Reynolds outlining their findings, I had a smile on my face knowing that we now had a second specimen. I was also impressed that they had correctly identified the discovery as another enormous jawbone from an ichthyosaur and recognised that it matched De la Salle's earlier find. I asked them whether they would like to join my team to study this fossil and they agreed.
Ruby Reynolds is now a published scientist who not only found but also helped to name a gigantic prehistoric reptile. There are probably not many 15-year-olds who can say that. She, her father and De la Salle have all contributed to our understanding of the ancient world.
Palaeontology is one of those sciences where anybody can make a significant contribution. You do not have to be a professor or a world expert. You just need a keen eye, a lot of patience and a little bit of luck.
It is remarkable to think that gigantic, blue whale-sized reptiles were swimming in the oceans around what was the UK hundreds of millions of years ago. These jawbones provide tantalising evidence that perhaps, one day, a complete skull or skeleton of one of these giants might be found.
Dean Lomax worked with Paul de la Salle, Marcello Perillo, Justin and Ruby Reynolds and Jimmy Waldron of the Dinosaurs Will Always Be Awesome Museum on the referenced research. He dedicates the work to Paul de la Salle who found the first surangular in 2016.
