|The tough, waterproof amnion was vital to the reptile's early evolutionary success.|
The amnion is also found in their descendants - the reptiles and the birds
Yet 312 million years ago a group of amphibians made a wild evolutionary deviation from the line taken by their moist-skinned cousins. They developed dry scaly skins and eggs containing a tough, waterproof membrane, the amnion. These newcomers were the first reptiles.
Their adaptations allowed them to spread into the deserts at the heart of their homeland continent, Pangaea, as well as the swamp forests in which they first evolved. Yet this early diversification is sparsely recorded. Now a 304 million year old fossil gives a tangible point and anatomical reference to this poorly preserved section in the history of life. And there is rather nice tale attached to its discovery.
In 1985 Michael Arsenault, aged nine, discovered the fossil on a beach whilst on holiday on Prince Edward Island, Canada. He slipped on a patch of algae and noticed that the slab of sandstone he had fallen on contained a line of vertebral discs. Convinced that he had found a dinosaur, his parents helped him extract the fossil, using shovels and garden tools, and lugged the 30 kilogram chunk of rock back to their house. They later showed it to local expert, Bob Grantham,
Grantham realised that the fossil was older than the dinosaurs based on the stratum from which it came. The specimen was later given to the Royal Ontario Museum in 2004 in exchange for a fee, which went towards Arsenault's education, and two replicas. A monograph on the species was published recently and the classification of Erpetonyx arsenaultorum revealed surprising results.
|The remarkably complete 304 million year old fossil of Erpetonyx |
arsenaultorum from Prince Edward Island, Canada
At 25 centimetres in length with small, peg-like teeth, it would have been similar in form to an iguana. Indeed the fossil is one of the most complete reptile skeletons from the Carboniferous period, meaning that its morphology can be reconstructed with a high degree of accuracy. Reptiles would come to dominate the Earth.
Erpetonyx is a valuable addition to the Carboniferous reptile record. The dinosaurs in turn would rule the planet for nearly 200 million years. Yet the reptile family were also the evolutionary forebears of the mammals and birds, both major players in modern ecosystems. The mark of the reptiles is indelibly stamped on the planet yet to understand their success fully, we must have a firm grasp on their evolutionary origins and early history. Erpetonyx is the first of many new discoveries.