155-Million-Year-Old Fossil Holds Clues About Land Animals’ Transition Back to Sea

Research posts

A recently discovered 155-million-year-old marine reptile fossil now in the Museum’s paleontology collections is providing scientists with new insight into the evolutionary trajectory of land-roaming animals that became aquatic.


Dorsal view of complete reptile fossil with extended limbs and long tail.

Catalog no. AMNH FARB 32768, Vadasaurus herzogi. The reptile has been named the newest member of the order Rhynchocephalia.

© AMNH/M. Ellison

The foot-long reptile, named Vadasaurus herzogi after the Latin for “wading lizard” and in homage to the German filmmaker Werner Herzog, was uncovered in limestone quarries near Solnhofen, Germany—an area that was once an ancient sea.

Researchers Mark Norell, Macaulay Curator in the Division of Paleontology and Gabriel Bever, a Museum research associate and assistant professor at Johns Hopkins University School of Medicine, identify Vadasaurus as a cousin of the pleurosaurs, a group of ancient marine reptiles that lived between 185-150 million years ago.

Long thought to have ancestors that once walked on land, pleurosaurs were fully adapted to sea life, with long eel-like bodies that were about five times the length of Vadasaurus and small limbs. Like pleurosaurs, Vadasaurus had a long and slender body, a tapered tail, and a triangular-shaped head. But the species retained larger limbs more characteristic of land-dwellers, offering a snapshot of an early stage of the return to water.

“Any time we can get a fossil like this that is so well preserved, and so significant in understanding a major environmental transition, it is very important,” says Norell. 


Graphic shows skull types of Vadasaurus, Palaeopleurosaurus, and Pleurosaurus and text indicating further differentiation.

A graphic demonstrating how Vadasaurus evolved to become fully aquatic. 

© R. Soc. open sci./G. Bever, M. Norell

By analyzing the Vadasaurus fossil, Norell and Bever found that the reptile likely used its limbs in the water for steering rather than paddling. What remains unknown, however, is just how much time Vadasaurus spent in the water.

“It may be that the animal developed its aquatic adaptations for some other reason, and that these changes just happened to be advantageous for life in the water,” says Bever.


Hand holding a tuatara.

Found in New Zealand, tuatara are the only living species of rhynocephalians left on Earth.

Courtesy of A. Santosa/Flickr

In the study, published in Royal Society Open Science, Norell and Bever classified Vadasaurus as the newest member of the order Rhynchocephalia. In addition to pleurosaurs, rhynocephalians include a single living species, New Zealand’s terrestrial reptile tuatara.


To learn more about another land-to-sea ancestral species, read about the terrestrial whale ancestor Pakicetus.