In May 2020, 11-year-old Ruby Reynolds and her father, Justin Reynolds, set off to Blue Anchor, a seaside village in Somerset, England, for a casual fossil-hunting expedition. While scanning the beach, Ruby stumbled upon a large piece of bone half-buried in the mud. Little did they know, this fossil was part of the largest marine reptile ever found.

Father and daughter contacted Dr. Dean Lomax, who had previously studied ichthyosaur fossils in the area. To Lomax’s astonishment, the bone Ruby found matched another large, fossilized jawbone discovered by fossil collector Paul de la Salle in 2016. These jawbones, once pieced together, revealed a gigantic species, now named Ichthyotitan severnensis — or “giant fish lizard of the Severn.”

Titans of the sea

When the dinosaurs ruled the land, other reptiles ruled the sea. Some of these reptiles grew to massive sizes and now, researchers may have found the largest of them. At 25 meters (82 feet), Ichthyotitan severnensis was an absolute beast.

At first glance, ichthyosaurs looked a bit like dolphins. They had streamlined bodies, long snouts, and powerful tails that allowed them to glide effortlessly through the water. However, unlike dolphins, which are mammals, ichthyosaurs were reptiles. They breathed air but were fully adapted to life in the ocean, never returning to land.

Ichthyosaurs first evolved around 250 million years ago during the early Triassic period. This period marked the beginning of the Mesozoic Era, often called Earth’s “middle age.” This era is divided into three major periods: the Triassic, Jurassic, and Cretaceous, each representing a different stage in the evolution of life on Earth.

Initially, ichthyosaurs weren’t notably large, but relatively quickly (in a few million years), they grew to gargantuan sizes. Researchers have found several ichthyosaurs that were larger than 15 meters (49 feet) long. But this one is way larger.

A massive find

The discovery of Ichthyotitan severnensis began a few years ago when Dean R. Lomax, a paleontologist affiliated with the University of Bristol and the University of Manchester in the UK, unearthed several large fossils. These fossils, resembling parts of an ichthyosaur’s jawbone, were massive, leading Lomax to believe they belonged to a sea giant.

The breakthrough came when Lomax and his colleagues discovered another jawbone just a few miles away. The researchers were able to piece the fossils together, much like a prehistoric puzzle, leading them to conclude they had found a new species of ichthyosaur. Though the size of the creature is still an estimate, researchers are confident it was one of the largest, if not the largest, marine reptiles in history.

An age of expansion

Ichthyotitan severnensis lived during a time known as the Rhaetian, at the end of the Triassic Period. Shortly afterward, around 201.3 million years ago, a mass extinction event wiped out many marine species. This included the giant ichthyosaurs. What caused this extinction is still debated. But scientists believe that massive volcanic activity in what is now the Atlantic Ocean caused dramatic shifts in the Earth’s climate, leading to the numerous extinctions.

While smaller ichthyosaurs continued to thrive into the Jurassic and Cretaceous periods, they never again reached the enormous sizes of their Triassic ancestors. Eventually, they too went extinct around 94 million years ago, leaving the oceans’ top predator niche to be filled by whales, other marine mammals and sharks.

The research was published in PLOS ONE.