By Dr. Becker
It's currently unknown whether modern-day snakes evolved from reptiles that lived on land or in the water. If they came from marine reptiles, it could be that their legs disappeared in order to help them move through the water.
On the other hand, if snakes evolved from land reptiles, they may have lost their legs to facilitate them moving through tight spaces underground.
Researchers from the University of Edinburgh and the American Museum of Natural History in New York City believe they may have solved the puzzle. Their new study suggests snakes came from a long line of land burrowers.
The Inner Ear Gives Clues to Snakes' Origins
The researchers built 3-D virtual models of the inner ears of 44 fossil and modern reptile species. The inner ear of burrowers has a distinct inflated appearance. The structural shape is associated with low-frequency hearing, which would be necessary to detect underground vibrations.
An ancient relative of modern snakes known as Dinilysia patagonica, which lived 90 million years ago, turned out to have the same inflated inner ear shape as a burrower. The researchers concluded that snakes likely came from burrowing reptile ancestors. They explained in the journal Science Advances:1
"A burrowing life-style predated modern snakes, but it remained as the main, if not exclusive, habit for basal lineages among crown snakes. Both D. patagonica and the hypothetical ancestor of crown snakes have a large vestibule that is associated with low-frequency hearing.
This suggests that ancestrally, crown snakes were able to detect prey and predator via substrate vibrations."
Four-Legged Snake Fossil Also Hints at Life on Land
While touring a German museum, paleobiologist David Martill, Ph.D. of the University of Portsmouth in England saw a specimen labeled "unknown fossil," which he believes is a snake with tiny legs.
"It's a tremendously important fossil, because it's the classic missing link … It's got a snake-like body but four little lizard-like legs," he told Science News.2Writing in the journal Science, the researchers noted:3
"Snakes are a remarkably diverse and successful group today, but their evolutionary origins are obscure.
The discovery of snakes with two legs has shed light on the transition from lizards to snakes, but no snake has been described with four limbs, and the ecology of early snakes is poorly known.
We describe a four-limbed snake from the Early Cretaceous (Aptian) Crato Formation of Brazil … The structure of the limbs suggests that they were adapted for grasping, either to seize prey or as claspers during mating."
Some experts, like Michael Caldwell, Ph.D. a paleontologist at the University of Alberta in Canada, aren't entirely convinced the fossil is in fact a four-legged snake, and some are suggesting a 3-D scan of the fossil would help set the record straight.
Snakes May Have Crawled Around With Dinosaurs
In previous research, Caldwell and colleagues also found four new species of snakes that date back to 167 million years old. This is the oldest known record of snakes and suggests they lived among the dinosaurs.4,5
The fossils included mostly skull bones, which shared many features with modern snake skulls, including teeth that curve backward and sit in sockets. It's long been thought that snakes first evolved to have long bodies that allowed them to constrict their prey.
However, Caldwell's finding suggests the specialized, flexible skull may have come first. It's thought that the early snakes had heads similar to modern-day snakes with shorter bodies and four limbs, but again definitive proof is lacking. Caldwell told Science News:6
"These things had specialized features of snake skulls 167 million years ago. That probably indicates that … the snake innovation was about the skull and feeding ecology, not becoming long and legless."
Interestingly, there's even a study that may explain how snakes lost their limbs. Researchers were able to transform a snake fossil into a 3-D model that revealed tiny 0.8-inch legs.
Small, regressed hind limbs and no front limbs were revealed, which suggests snakes' legs likely began growing more slowly or for a shorter period of time until they were eventually lost.7