A fossil jawbone found by a British girl and her father on a beach in Somerset, England, belongs to a gigantic marine reptile dating back to 202 million years ago that appears to have been among the largest animals ever on Earth.

Researchers said the bone, called a surangular, was from a type of ocean-going reptile called an ichthyosaur.

Based on its dimensions compared to the same bone in closely related ichthyosaurs, the researchers estimated that the Triassic Period creature, which they named Ichthyotitan severnensis, was between 22 and 26 meters long.

That would make it perhaps the largest-known marine reptile and would rival some of the largest baleen whales alive today. The blue whale, considered the largest animal ever on the planet, can reach about 30 meters long.

Marine reptiles ruled the world's oceans when dinosaurs dominated the land. Ichthyosaurs, which evolved from terrestrial ancestors and prospered for about 160 million years before disappearing roughly 90 million years ago, came in various sizes and shapes, eating fish, squid relatives and other marine reptiles and giving birth to live young.

Ichthyotitan is known only from two jawbones, the one found by Ruby Reynolds and her father Justin Reynolds in 2020 at Blue Anchor, Somerset, and another from a different Ichthyotitan individual found in 2016, along the Somerset coast at Lilstock.

Ruby Reynolds, who was 11 at the time and is now 15, was fossil hunting on the beach with her father when they spotted a piece of the surangular. Ruby continued to search the area and found a second piece — much larger than the first — partly buried in a mud slope. They subsequently contacted Dr Lomax, an ichthyosaur expert, and additional sections of the bone were unearthed.

Ichthyotitan was a member of a family of giant ichthyosaurs called shastasauridae, and lived 13 million years later than any of the others known to date, suggesting these behemoths survived until a global mass extinction event that doomed numerous types of animals about 201 million years ago at the end of the Triassic.

No fossils of the rest of Ichthyotitan's skeleton have been discovered, but the researchers have been able to discern its appearance based on other members of its family including Shonisaurus from British Columbia, Canada.

The surangular is a long, curved bone at the top of the lower jaw, just behind the teeth, present in nearly every vertebrate living or extinct, apart from mammals. Muscles attached to this bone generate bite force.

Source: ABC News