The largest sea reptile ever found?

A father and daughter have discovered what could be a remnant of the largest known marine reptile. Justin and Ruby Reynolds found a piece of jaw belonging to an ichthyosaur, dubbed Ichthyotitan severnensis, on a beach at Blue Anchor in Somerset. It was then sent to Dean Lomax, a palaeontologist at the University of Manchester.…

Dean - To go back in time a little bit, not quite to the Jurassic of the Triassic millions of years ago. But I received an email initially way back in May, 2016 about a jawbone that was found in Somerset. And then after studying that specimen, which was found by Paul de la Salle, we described it in 2018 and we determined that it was a really unusual jawbone from a type of ancient marine reptile called an ichthyosaur. And because the age of which this comes from is about 202 million years old, right at the end of the Triassic, we knew then that it was something unusual and very likely came from a really big ichthyosaur. But we were kind of hesitant about giving it a name or working out exactly what type of species of ichthyosaur it was, and so entered this new discovery. Justin and Ruby managed to find my scientific study from 2018, reached out and were like, 'Hey Dr. Lomax, we think we found another one of these giant ichthyosaur jaw bones.' And of course you can imagine my huge grin on my face because I was like, 'absolutely, yes you have.'

Will - How do you then go from these two fairly abstract samples to being able to scale it up to make assumptions or predictions about the entirety of the organism involved?

Dean - Being completely honest, with just two giant jaw bones, it is impossible to say with absolute certainty just how large our new species of ichthyosaur was. However, there are other ichthyosaurs that have been found that are on the kind of size range lengthwise between like 15 to 21 metres. The biggest one was in the region of maybe 40 to 50, maybe a little bit more percent complete. And this ichthyosaur, which has a name called Shonisaurus sikanniensis, has an estimated skeleton length of 21 metres. Now by comparing Paul's original 2016 discovery and Justin and Ruby's discovery with the same bone, which is called a surangular, which is a bone right at the back of the lower jaw, we can work out that the specimens are about 25% larger. So by doing a little bit of kind of like quick maths and using a simple scaling factor, we can estimate that our ichthyosaur is upwards of about 26 metres. And then comparing it further with other ichthyosaurs, smaller species and those kind of bridging the gap between the very small ones and the really big ones, we can basically work out that our ichthyosaur would've been around about the 20 to 26 metre mark with most of the averages coming out at 25 metres.

Will - It's a very exciting finding, but I still do need some reassurances because growing up my hero was of course Liopleurodon, another marine reptile which, originally, thought to be 20 plus metres. And in the years since has been revised down to six, which is a remarkable shrinkage. It should probably be about three feet by next year. How can you assure me that this isn't going to happen to this as well?

Dean - <Laugh> I kind of anticipated this question would come at some point that makes me laugh. At the time, if I remember rightly, it was based on some really fragmentary vertebrae and then there's been a few other kinds of scalings up of Liopleurodon based on their teeth. To be honest, teeth and vertebrae are not the best bones to try and scale up an animal in size. Because just for example, I studied a whole bunch of different ichthyosaurs, thousands of them now over the years. And by looking at, say, some vertebrae of an individual that's 10 metres long. Those vertebrae may only be say, 12 centimetres across, versus you might find another iau that's like eight metres long and those vertebrae may be 15 centimetres across. So vertebrae aren't ideal. That's why we have much more confidence in our scaling of that kind of 20 to 26 metre mark because we know that we have an ichthyosaur from British Columbia that was definitely at the 21 metre range. So looking at our new specimens, Paul's and Justin and Ruby's, we have something that we definitely can compare to, and we have the same bone that's preserved in that animal as well. So it gives us a much, much, much more reliable estimate and scaling factor.

Will - Okay, well I'm ready to love again. But it does make you think, given that the fossil record is a fraction of a fraction of a fraction of what was actually alive at the time, what could be out there still ready to be discovered and something really could perhaps have the potential to knock the blue whale off its giant perch?

Dean - That's quite right. And I said for a little while, especially off the back of Paul's discovery in 2016 and our research in 2018, that we think that in time potentially maybe we'll have a skeleton or at least a big skull of one of these giants found. As part of our research in this new study and the 2018 study, we also looked at some bones that were found here in the UK. And these bones were originally over 150 years ago. They were very similar. They're big cylindrical chunks of bone. But back over 150 years ago, the scientists then, and even right up to this day, almost to a point about 10 years ago, people were still considering them to be the upper arm bone, say a humerus or upper leg bone or a femur of a terrestrial animal, like a dinosaur. But in actual fact, they are also bones from the lower jaws of giant ichthyosaurs. And one of them is about 30 to 40% larger than the bone from the one in Canada. So that's when you start to get to the realms of are we dealing with something that was even maybe 30 plus metres? And then are we dealing with a thing that could take the blue whale off that very top of the largest animals ever? Maybe, maybe not. This is the thing, as you say, this is the fossil record and that's why it always reveals its kind of secrets and things. And this is just a little bit more of that kind of tantalising evidence of one of these mysterious giants that lived at the very end of the Triassic period 202 million years ago.