IT was a mean, aged, mutant dino-turtle which swam the oceans many millions of years ago.

But unlike its distant descendants today, the scaly beast didn't have the characteristic which defines turtle-kind today, and had no shell at all. 

Yet this long-lost relative of the modern sea-going reptiles is helping inform a fresh understanding of their evolution after its fossilised skeleton was found in China, representing one of the earliest examples of this group of animals ever found.

Stretching two-and-a-half metres long, the creature lived 228 million years ago and swam in warm coastal waters at a time when the earliest dinosaurs were getting established on the planet.

Experts at the National Museums Scotland, who worked on a study of the fossilised remains, said that it was probably just as at home on the land where it could root around in the mud for prey and items to eat.

The Herald:

The turtle probably swam as well as walked

Like turtles today, it most likely had a bony 'beak' to tackle its food but was equipped with legs instead of flippers, meaning it would have felt at ease out of the water.

And while it lacks the carapace and plastron (shell) that is so characteristic of the species, the ‘scaffolding’ for the building of the shell is clearly in place with extremely broad ribs spreading out to the sides forming a wide, oval-shaped body  - just like a modern-day turtle. 

Dr Nick Fraser, Keeper of Natural Sciences at National Museums Scotland, co-authored the study of the newly-discovered fossil along with colleagues at the Chinese Academy of Sciences, the Field Museum of Natural History and the Canadian Museum of Nature.

When he first saw it, the imprint was still encased completely in rock, and only the vague outline of the body could be seen.

The Herald:

The fossil skeleton

Dr Fraser said: “Even then it was clear that this was a bit of a monster and unlike anything else I had seen in these very rich deposits.

 "A turtle was just one of many things that went through my mind, but I was truly stunned when I saw the whole fossil fully prepared”. 

Life on earth 228 million years ago, dubbed the Triassic epoch, was going through a series of rapid changes, following the separation of the super-continent Pangea into distinct landmasses by continental drift.

 The era saw the first of the dinosaurs appear, although they mostly small, with monsters such as Tyrannosaurus Rex still millions of years from evolving.

However, it was also marked by a mass extinction of other non-dinosaur reptiles, such as semi-aquatic crocodile cousins called phytosaurs, big four-legged meat-eaters called rauisuchians and four-legged armoured plant-eaters called aetosaurs, along with a huge number of  creatures living in the sea.

One of the more bizarre animals known to science from the period is the dome-headed reptile Triopticus Primus, who came equipped with a bony 'helmet' on the top of its head.

Yet while these creatures died out, the fossil turtle's lineage would survive until the modern day, although vastly changed through evolution.

The Herald:

The animal had a beak-like mouth

Dr Fraser said: “This impressively large fossil is a very exciting discovery that gives us another piece in the puzzle of turtle evolution.

"It shows that early turtle evolution was not a straightforward, step-by-step accumulation of unique characteristics but was a much more complex series of events that we are only just beginning to unravel.”

Pictures: National Museums of Scotland/Yu Chen