Mention snakes and the image that comes to mind is that of a stealthily gliding reptile. It turns out that this was not always the case. Ancient snake fossils indicate that the reptiles once had legs, just like the rest of us. So why did snakes decide to shed them in favor of the slither that sends chills down our spines? That is a mystery researchers have been trying to solve for some time.
There are currently two schools of thought. Some scientists believe that the reptiles dispensed with their legs to enable them to dwell in water. Others think that snakes evolved from burrowing lizards and shed their limbs over time, as they stretched and became longer.
The first proof that the second theory is more likely came in July 2015. David Martill paleobiologist at the University of Portsmouth was leading a field trip at Germany's Museum Solnhofen when he stumbled upon a rare fossil of a four-legged snake that inhabited the planet 113-million years ago.
Measuring 20cm from head to toe, the perfectly preserved skeleton had two tiny (1cm long) front legs complete with elbows, wrist, and hands. The reptile's hind legs were a little longer and larger. Though the limbs were too small for walking they were perfect for grabbing prey which is why the scientist named it Tetrapodophis amplectus (four-legged hugging snake).
A closer examination of the skull revealed it had no adaptations to survive in water. It did, however, appear perfectly suited for burrowing on land. This led many scientists including Martill to conclude that slithering snakes had evolved on land, not water. But many researchers were skeptical of the theory, especially since they believed that the Tetrapodophis amplectus was not a snake but a lizard.
Now a new study conducted by a group of Scottish and American scientists further validates that snakes probably ditched their legs to slither through underground burrows, allowing them to avoid predators and pounce upon unsuspecting prey.
The team led by Hongyu Yi at Edinburgh’s School of GeoSciences reached the conclusion after studying a 90 million-year-old skull of the Dinilysia patagonica an ancient reptile that is closely related to the modern-day snake. The discovery was possible thanks to new CT scan technology that allowed them to create 3D models of the skull and compare them to that of modern snakes and lizards.
The researchers were looking to see if the reptiles shared the same unique ear structure that is found in burrowing animals. Sure enough, though the ear canals and cavities have adapted further in modern-day burrowing snakes and lizards, there remains a substantial similarity. Snakes that currently live in water or above ground do not have the same adaptations.
The evidence was enough for the scientists who published their findings in the online journal Science, to conclude that snakes had evolved on land. They believe that as the reptile's hearing sharpened and became accustomed to their subterranean habitat, its limbs began to recede, until they disappeared altogether.
While such evolution takes time, it is not unheard of especially in animals who are constantly evolving to survive. Unfortunately, in the modern day world many of the adaptations are driven not driven by careless human activities - Like coral adapting to warmer temperatures or fish becoming resistant to toxins to survive our increasingly polluted waters.
Resources: BBC.co.uk, wikipedia.org, wired.com, sciencedaily.com, universityofedinburgh.com