Sunday, July 26, 2015

Snake ancestor had four legs and 'dug burrows'

The snake's legs were just a few millimetres long

A 113-million-year-old fossil from Brazil is the first four-legged snake that scientists have ever seen.
Several other fossil snakes have been found with hind limbs, but the new find is estimated to be a direct ancestor of modern snakes. Its tiny, delicate arms and legs were not used for walking, but probably helped the creature to grab its prey.
The fossil shows adaptations for burrowing, not swimming, strengthening the idea that snakes evolved on land.
"This is the most primitive fossil snake known, and it's pretty clearly not aquatic," said Dr Nick Longrich.

Speaking to Science in Action, Dr Longrich explained that the creature's tail wasn't paddle-shaped for swimming and it had no sign of fins; meanwhile its long trunk and short snout were typical of a burrower. It has a lot of very advanced snake features including its hooked teeth, flexible jaw and spine - and even snake-like scales.
"It's pretty straight-up adapted for burrowing," he said.
"And there's the gut contents - it's swallowed another vertebrate. It was preying on other land animals, which is a snake feature."
"It was pretty unambiguously a snake. It's just got little arms and little legs."
Deadly embrace?
At 4mm and 7mm long respectively, those arms and legs are little indeed. But Dr Longrich was surprised to discover that they were far from being "vestigial" evolutionary leftovers, dangling uselessly."They're actually very highly specialized - they have very long, skinny fingers and toes, with little claws on the end. What we think [these animals] are doing is they've stopped using them for walking and they're using them for grasping their prey."

four-legged snake fossil
The 20cm snake lived about 113 million years ago, at the same time as many species of  dinosaurs   
That comparatively feeble grasp, which may have also been applied during mating, is where the species gets its name. Tetrapodophis, the fossil's new genus, means four-footed snake, but amplectus is Latin for "embrace".
"It would sort of embrace or hug its prey with its forelimbs and hindlimbs. So it's the huggy snake," Dr Longrich said.
In order to try to pinpoint the huggy snake's place in history, the team constructed a family tree using known information about the physical and genetic make-up of living and ancient snakes. That analysis positioned T. amplectus as a branch - the earliest branch - on the very same tree that gave rise to modern snakes.

fossil snake stomach contents

Judging by its stomach contents, the snake's final meal was a small, unfortunate vertebrate 
All the latest findings suggest that the ancestor of all snakes was a terrestrial animal... which lived partially underground.

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