This Ancient Reptile Was One of the Most Massive Creatures That Ever Lived

A fossil jawbone found in England suggests the ‘sea monster’ was nearly the size of a blue whale

Nobumichi Tamura

Blue whales, which can grow to around 100 feet in length, are often touted as the largest animals to have ever existed on earth. But as John Pickrell at National Geographic reports, paleontologists in England recently discovered a bone from an ancient 'sea monster' that seems to have been just as big, hinting at the possibility other ancient sea creatures were just as massive.

In 2016, amateur fossil hunter Paul de la Salle was walking the beach in Lilstock, a town in Somerset in the southwest of England, when he found a large fossil. He believed it belonged to an ichythosaur, a dolphin-shaped carnivorous marine reptile with a long, toothy snout that lived in the oceans during the age of the dinosaurs. He continued to search the area, discovering more pieces of the fossil, which, when fit together, make up a 3.2-foot section of jawbone.

De la Salle got in touch with ichthyosaur experts Dean Lomax at The University of Manchester and Judy Massare, professor emerita of geology at SUNY College at Brockport. According to a press release, the researchers dated the bones to 205 million years ago, and estimate that in life the Lilstock ichthyosaur would have been up to 85 feet long, edging well into blue whale territory. A description of the fossil appears in the journal PLOS One.

“This bone belonged to a giant,” Lomax tells Reuters. “The entire carcass was probably very similar to a whale fall in which a dead whale drops to the bottom of the sea floor, where an entire ecosystem of animals feeds on the carcass for a very long time. After that, bones become separated, and we suspect that's what happened to our isolated bone.”

This new specimen is about 25 percent larger than the previous largest ichythyosaur, a 69-foot-long creature including half a skull, backbone ribs and part of the tail called Shonisaurus sikanniensis found in British Columbia, reports Laura Geggel at LiveScience.

“A comparison with the back of the Shonisaurus jaw indicates that our specimen is larger,” Massare, a co-author of the study, tells Geggel. “But we know much less about it because it is just one bone.”

As Pickrell reports, the find has led the team to reassess other fossils found along the English coast. In particular, they reexamined a group of large bones found in cliffs near the village of Aust in Gloucestershire, England. These were previously interpreted as being limbs from terrestrial dinosaurs, but the classification never perfectly lined up.

“We compared it with these Aust bones, and as soon as I saw it in person, my jaw just hit the floor,” Lomax tells Pickrell. “I realized this was a giant ichthyosaur and the biggest thing ever found in the U.K.” The Aust fragments may have once belonged to creatures even larger than the Lilstock beast.

Paleontologist Darren Naish from the University of Southampton, who has studied the Aust bones and come to the same conclusion, tells Pickrell that these new finds are astonishing and agrees that they suggest that these ichthyosaurs neared or even exceeded modern baleen whales in size.

If that’s the case, it’s a big deal. Many researchers are investigating the question of how baleen whales got so big. Studies suggest for the whales, their massive size is a relatively recent phenomenon, perhaps fostered by giant clouds of krill that lived on the edges of ice sheets during the Ice Ages. But why certain ichthyosaur species would grow to such mammoth proportions remains a matter of speculation.

Ichthyosaurs appeared during the start of the Triassic, some 250 million years ago. Though they initially lived along coasts, they eventually moved to deeper water. At their height, they filled many niches, from ambush predator to suction feeder and were among the most successful animals in the oceans. But about 90 million years ago, almost 25 million years before the dinosaurs disappeared, ichthyosaurs died out. Researchers are currently trying to understand what drove the once-plentiful sea reptiles to extinction.

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