Fossil of ancient 12-foot turtle thought to be one of biggest ever discovered

An illustrated reconstruction of the large Cretaceous Period sea turtle Leviathanochelys aenigmatica, which lived about 83 million years ago (Museu de la Conca via REUTERS)
An illustrated reconstruction of the large Cretaceous Period sea turtle Leviathanochelys aenigmatica, which lived about 83 million years ago (Museu de la Conca via REUTERS)

Fossils of a 12-foot turtle that have been found in north eastern Spain are thought to date back some 83 million years.

The Leviathanochelys aenigmatica is said to have been one of the largest sea turtles to have ever lived, scientists have said.

Fossilised remains of the turtle - measuring nearly four metres in length - were discovered in the Cal Torrades locality and have been excavated over several years.

The largest known sea turtle is the extinct Archelon, which lived in the seas surrounding the North American continent somewhere between 66 to 100 million years ago.

The excavation site where fossils of the large Cretaceous Period sea turtle Leviathanochelys aenigmatica where found in Catalonia (Museu de la Conca via REUTERS)
The excavation site where fossils of the large Cretaceous Period sea turtle Leviathanochelys aenigmatica where found in Catalonia (Museu de la Conca via REUTERS)

The Archelon was around 4.6m long and weighed up to 3.2 tonnes. The Leviathanochelys, meanwhile, measures 3.74m.

No known European marine turtle - extinct or living - has exceeded 1.5m in shell-length, the researchers said.

A team of scientists led by Angel Lujan of the Autonomous University of Barcelona analysed the remains of the turtle, which were excavated between 2016 and 2021.

They found a fragmented but almost complete pelvis and parts of the upper shell, which date to the Campanian Age - somewhere between 83.6 to 72.1 million years ago.

The Leviathanochelys aenigmatica excavation site (PA)
The Leviathanochelys aenigmatica excavation site (PA)

One key feature that caught the researchers eyes is a distinctive bone that protrudes forwards from the front of the pelvis - something that is not seen in other marine turtles.

This indicates that Leviathanochelys represents a new group of ancient marine turtles, the experts said.

The researchers believe this protrusion may be related to the creature's respiratory system.

Based on the size of the pelvis, the scientists calculate that Leviathanochelys could have reached a body length of up to 3.74 metres.

They estimate the maximum width of Leviathanochelys' pelvis was 88.9cm, making it slightly larger than the biggest estimates for Archelon's best-known specimen (81cm).

These findings indicate that gigantism in marine turtles developed independently in different lineages in both North America and Europe, the researchers said.