Secrets of an ancient reptile

Very occasionally, exceptionally well-preserved fossils reveal new clues about poorly understood creatures. Complete, articulated skeletons are rare and, when found, offer rich insight for palaeontologists. One of our research fellows, Dr James Neenan, has been involved with just such a discovery and description, of an armoured reptile from the Middle Triassic named Eusaurosphargis dalsassoi.

A beautifully-preserved fossil found in the Alps in eastern Switzerland has revealed the best look so far at this animal. The findings about its anatomy and probable lifestyle were somewhat unexpected, according to a paper published in Scientific Reports today, led by Dr Torsten Scheyer at the University of Zurich and co-authored by James.

At just 20 cm long, the specimen represents the remains of a juvenile. Yet large portions of its body were covered in armour plates, with a distinctively spiky row around each flank, protecting the animal from predators. Today’s girdled lizards, found in Africa, have independently evolved a very similar appearance even though they are not closely related to Eusaurosphargis.

The new fossil, found in the Prosanto Formation at Ducanfurgga, south of Davos in Switzerland, is not the first material of Eusaurosphargis to be discovered. The species was originally described in 2003 based on a partially complete and totally disarticulated specimen from Italy. This was found alongside fossils of fishes and marine reptiles, leading scientists to believe that Eusaurosphargis was an aquatic animal.

However, the detail preserved in the new specimen shows a skeleton without a streamlined body outline and no modification of the arms, legs or tail for swimming. This suggests that the reptile was in fact most probably adapted to live, at least mostly, on land, even though all of its closest evolutionary relatives lived in the water.

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. 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 fossilised. – Dr James Neenan

The findings from the research team are published in Scientific Reports as ‘A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny’.