The remains of a massive marine reptile have been found in the mouth of the River Severn in Great Britain. The ichthyosaur’s lower jaw bones were probably more than two meters long, and the entire animal was possibly more than 25 meters, as a research team reports in the journal “PLOS One”.

The fragments of a jawbone were found in 2020 by Ruby Reynolds, then eleven years old, who was looking for fossils with her father Justin on the beach at Blue Anchor in Somerset. The two recognized that the bones were similar to another find described in 2018.

“Giant fish lizard from the Severn”

This so impressed ichthyosaur expert Dean Lomax from the University of Manchester that he invited her to the research team that would describe the find. Ruby is now a published scientist, they said. Not only did she find a gigantic prehistoric reptile, she also helped name it, Lomax said. Its technical name is now Ichthyotitan severnensis, which can be translated as “gigantic fish lizard from the Severn”.

The lower jaw bone found by father and daughter Reynolds is more complete and better preserved than the one described in 2018. He confirmed some unique features of the bone fragments first found, the location of which is about ten kilometers from Blue Anchor. “It’s quite remarkable that gigantic ichthyosaurs the size of a blue whale swam in the oceans around the United Kingdom during the Triassic,” Lomax points out. The Triassic is the oldest period of the Mesozoic; it began around 252 million years ago and ended around 201 million years ago.

More bones needed to confirm

Reconstruction of the fragments revealed that the lower jaw bone was about 2.3 meters long. The study authors compared the bone, among other things, with a lower jaw bone from the ichthyosaur species Besanosaurus leptorhynchus, which was around 5.4 meters long. Distinctive features of the remains of Ichthyotitan severnensis were about five times as far apart as the comparable bones of Besanosaurus, so the scientists assume that the body length was five times larger. “However, it is worth noting that this is based on fragmentary remains and therefore more complete specimens are required to confirm the giant size,” they write.

“These jawbones provide a tantalizing hint that a complete skull or skeleton of one of these giants may one day be found,” Lomax said. The 25 meter length could possibly even be exceeded: An examination of the bone tissue by a co-author of the study, Marcello Perillo from the University of Bonn, showed that the ichthyosaur from Blue Anchor Beach was probably not yet fully grown.

Also the youngest giant species

If the data are confirmed, Ichthyotitan severnensis would not only be the largest ichthyosaur species discovered to date, but also the youngest: The fossils come from a rock formation that is around 202 million years old – 13 million years less than previously known giant ichthyosaurs.

201 million years ago, at the end of the Triassic, the fifth largest mass extinction in Earth’s history occurred, which probably also killed all of the large ichthyosaurs. After that, the marine reptiles never reached a comparable size again. They disappeared completely around 93 million years ago.