The Marine Reptile That Wasn’t –  Eusaurosphargis dalsassoi

A team of scientists from Zurich University and the University of Oxford have resolved a scaly, fourteen-year mystery concerning a small reptile that lived some 241 million years ago in the Middle Triassic.  The little diapsid named Eusaurosphargis dalsassoi has had quite a chequered history, but thanks to a remarkable fossil find, palaeontologists have a much better idea of what this reptile looked and equally importantly where it lived.  This animal was very much at home on land and not a marine reptile as previously thought.

An Illustration of Eusaurosphargis dalsassoi

Eusaurosphargis dalsassoi illustrated.

Picture credit: Beat Scheffold, Palaeontological Institute and Museum, University of Zurich

Fossil Discovery in 2003

Named from a single, disarticulated specimen found in marine strata on the Swiss-Italian border some fourteen years ago Eusaurosphargis was thought at first to be some form of fish, after all, the fossil was found in rocks formed from sediment laid down in a shallow lagoon.

Once the skeleton had been prepared, the fossil material was identified as a diapsid reptile and the taphonomy suggested that this was a reptile that lived in the sea.  Taphonomy is the study of the fossilisation process.  It concerns everything that happens to an organism from death until the time when, if serendipity permits, its fossil is discovered.  A new fossil find, this time from the Grisons Mountains (Graubünden canton of Switzerland), a much more complete and articulated specimen, has revealed the true nature of Eusaurosphargis, it was definitely a land-lubber and as such has a superficial similarity to the extant girdled lizards (Cordylidae) of southern Africa.

A Beautifully Well-Preserved Fossil Proves Eusaurosphargis was Terrestrial

The articulated fossil skeleton of Eusaurophargis.

Picture credit: Torsten Scheyer, Palaeontological Institute and Museum, University of Zurich

No Sign of Marine Adaptations

The Swiss specimen measures around twenty centimetres in length and as such, it represents a juvenile.

However, the skeleton shows a flange of osteoderms on the side of the body along with a number of bony scales on its back.  The sprawling limbs show no signs of adaptation for a swimming lifestyle and the tail is very short, so short, that in water it would not have provided much propulsion.  This fossil, excavated from the Prosanto Formation near Ducanfurgga at an altitude of 2,740 metres, strongly supports the idea that this was a terrestrial animal.

Writing in the academic journal “Scientific Reports”, the Anglo-Swiss team of researchers led by Torsten Scheyer, a palaeontologist at the University of Zurich, and James Neenan from the Oxford University Museum of Natural History have concluded that the carcass was washed off a nearby island into the sea basin and became embedded in the finely layered marine sediments after death.

Convergent Evolution

Commenting on the superficial resemblance between the Triassic Eusaurosphargis and modern-day members of the Cordylidae family, Dr Scheyer explained:

“This is a case of convergent development as the extinct species is not closely related to today’s African lizards.”

The Site of the Fossil Discovery – in the Middle of a Mountain Range

The location of the Eusaurosphargis fossil discovery.

Picture credit:  Christian Obrist

The Irony of the Phylogeny of Eusaurosphargis dalsassoi

Based on this new, and much better-preserved fossil material, the research team were able to conduct a more detailed phylogenetic study of E. dalsassoi to establish where, in the extremely diverse Diapsida this little reptile should be nested.  The phylogenetic analysis indicates that its closest relatives were marine reptiles, animals such as ichthyosaurs.  Eusaurosphargis may even be the sister taxon to Helveticosaurus, a Middle Triassic marine reptile, fossils of which, also come from Switzerland.