Saturday, 28 July 2012

On The Origin Of Snakes

Snakes are rather alien creatures. The way they move, their unblinking eyes and their lifestyle is far removed from almost all other vertebrates. Yet despite these unique qualities, tracking down their evolutionary past has proved a difficult job. Their skeletons are delicate and are broken down easily by decomposing organisms, resulting in a rather scanty fossil record. As a result, much of their evolutionary history has been reconstructed from their physiology.

The jaws of Coniophis precedens
Theories suggested that their unblinking, membrane-covered eyes, sleep form and lack of ears derived from watery origins. The earliest known snake fossils come from early Cretaceous formations. Found in formations of a similar age were fossils of aquatic reptiles known as mesosaurs which had completely lost their limbs. What little fossil evidence there was seemed to concur with the water origins theory.

Yet new remains of ancient serpents is challenging this long-held view. Earlier this year a team of palaeontologists, led by Dr Nicholas Longrich from Yale University, uncovered 65 to 70 million year old fossils of a creature known as Coniophis precendens, from eastern Wyoming. The oldest known snake fossils, which are of a very closely related genus, only predate this creature by 40 million years.

What makes Coniophis important is the locality from which its remain were uncovered. The entire area was once a floodplain. If snakes originated from water-dwelling lizards, Coniophis would have still had some features which hinted at its marine past owing to its position close to the base of the snake family tree. 'This thing quite probably would have had small legs,' said Dr Longrich. Features along its spine also suggested that it was a burrowing creature and a study of the jaws indicated that it fed on soft-bodied prey.

The main difference between Coniophis and modern day snakes is that it had inflexible jaws, restricting the size of the prey it could feed on. In the end, it seems that this creature was a transitional form, combining a snake's body with a lizard's head. Increased pressure from changing climates and environments would have driven these burrowing snakes out, but their legs, originally used to propel themselves through and dig narrow burrows, would have been useless and a hindrance.

Snakes with shorter legs and more elastic jaws could move faster and feed on a wider range of prey, making them more successful, giving rise eventually to the modern snakes' blueprint. More fossils will be needed to confirm this new theory, but even without supporting evidence, it still holds up better than the tenuous marine origins hypothesis. It is now a case of wait and see.