Eusaurosphargis dalsassoi: Exceptional Ancient Lizard Fossil Astonishes Scientists

A fossil plate of Eusaurosphargis dalsassoi. The fossil is the most complete specimen ever found. Torsten Scheyer/Paleontological Institute and Museum?University of Zurich

Prehistoric creatures may have been dead for millions of years but they can still surprise you.

An exceptionally well-preserved fossil found in the Swiss Alps in Europe has made scientists change their understanding of an ancient reptile species— Eusaurosphargis dalsassoi, first discovered in 2003. Now scientists believe that the armored reptile crawled on land rather than swam in the water, according to a paper published in Scientific Reports Friday.

The specimen, found in the Prosanto Formation at Ducanfurgga, south of Davos in Switzerland, is just 20cm (8 inches) long and constitutes the remains of a juvenile.

The first example of the species was described in 2003, but the fossil was only partially complete. It was found near remains of fish and marine reptiles, so researchers thought the animal it represented was aquatic.

But the new discovery is much more complete, described by the study's authors as "exceptionally preserved," and shows that Eusaurosphargis had a non-streamlined body and limbs that were not adapted for swimming, suggesting the creature was entirely or almost entirely land-based—even though its closest relatives were more waterborne.

It also boasts "extensive, complex body armour, mostly preserved in situ, along its vertebrae, ribs, and forelimbs," according to the study, described as the " most outstanding" feature of the fossil. The creature also had a "deep skull with a short and broad rostrum," the researchers say.

Eusaurosphargis dalsassoi
Reconstruction of Eusaurosphargis dalsassoi. Beat Scheffold, Paleontological Institute and Museum, University of Zurich

"As a whole, the anatomical features support an essentially terrestrial lifestyle of the animal," the study reads.

"Until this new discovery we thought that Eusaurosphargis was aquatic, so we were astonished to discover that the skeleton actually shows adaptations to life on the land," said James Neenan, a research fellow at Oxford University Museum of Natural History and co-author of the new paper. "We think this particular animal must have washed into the sea from somewhere like a beach, where it sank to the sea floor, was buried and finally fossilized."