Giant, 82-foot lizard fish discovered on UK beach could be largest marine reptile ever found

Scientists have unearthed the remains of a gigantic, 200 million-year-old sea monster that may be the largest marine reptile ever discovered.

The newfound creature is a member of a group called ichthyosaurs, which were among the dominant sea predators during the Mesozoic Era (251.9 million to 66 million years ago). The newly described species lived during the end of the Triassic Period (251.9 million to 201.4 million years ago).

Ichthyosaurs had already attained massive sizes by the early portion of the Mesozoic, but it was not until the late Triassic that the largest species emerged.

While the Mesozoic is known as the age of the dinosaurs, ichthyosaurs were not themselves dinosaurs. Instead, they evolved from another group of reptiles. Their evolutionary path closely mirrors that of whales, which evolved from terrestrial mammals that later returned to the sea. And like whales, they breathed air and gave birth to live young.

The newly discovered ichthyosaur species was unearthed in pieces between 2020 and 2022 at Blue Anchor, Somerset in the United Kingdom. The first chunk of the fossil was noticed atop a rock on the beach, indicating that a passerby had found it and set it there for others to examine, the researchers explained in the paper. The researchers published their findings April 17 in the journal PLOS One.

The reptile’s remains are made up of a series of 12 fragments from a surangular bone, which is found in the upper portion of the lower jaw. The researchers estimate the bone was 6.5 feet (2 meters) long and that the living animal was about 82 feet (25 m) long.

The researchers named the sea monster Ichthyotitan severnensis, meaning giant lizard fish of the Severn, after the Severn Estuary where it was found. The team believes it is not only a new species but an entirely new genus of ichthyosaur. More than 100 species are already known.

A giant pair of swimming Ichthyotitan severnensis . (Image credit: Gabriel Ugueto, CC-BY 4.0 )

A number of rib fragments and a coprolite, or fossilized feces, were found in the area as well, but they were not definitively attributed to the same animal.

The sediments in which these specimens were found contained rocks that indicated earthquakes and tsunamis occurred during that time, which suggests that this species lived during a time of intense volcanic activity that may have led to a massive extinction event at the end of the Triassic according to the researchers.

A similar specimen was discovered in Lilstock, Somerset in 2016 and described in 2018. Both were found in what is known at the Westbury Mudstone Formation, within 6 miles (10 kilometers) of each other. This ichthyosaur was estimated to have been as much as 85 feet (26 meters) long, although the authors of the latest study believe it was slightly smaller.

The previous contender for the largest marine reptile was another ichthyosaur, Shonisaurus sikanniensis, which was up to 69 feet (21 m) long. S. sikanniensis appeared 13 million years earlier than I. severnensis and was found in British Columbia, making it unlikely that the new discovery represents another specimen of the previously known species.

A similarly massive ichthyosaur called Himalayasaurus tibetensis, which may have reached lengths of 49 feet (15 m), was discovered in Tibet and described in 1972. It dates to the same period, meaning that it probably is not the same species as the new discovery either.

I. severnensis was likely among the last of the giant ichthyosaurs, the researchers claim. Ichthyosaurs persisted into the Cenomanian Age (100.5 million years ago to 93.9 million years ago) of the late Cretaceous Period (100.5 million to 66 million years ago). They were eventually supplanted by plesiosaurs — long-necked marine reptiles that went extinct at the end of the Cretaceous, alongside all non-avian dinosaurs.