Mystery of how snakes lost their legs solved by reptile fossil

November 27, 2015
Modern snake skull, with inner ear shown in orange. Credit: Hongyu Yi

Fresh analysis of a reptile fossil is helping scientists solve an evolutionary puzzle - how snakes lost their limbs.

The 90 million-year-old skull is giving researchers vital clues about how snakes evolved.

Comparisons between CT scans of the fossil and modern reptiles indicate that snakes lost their legs when their ancestors evolved to live and hunt in burrows, which many snakes still do today.

The findings show snakes did not lose their limbs in order to live in the sea, as was previously suggested.

Scientists used CT scans to examine the bony inner ear of Dinilysia patagonica, a 2-meter long reptile closely linked to modern snakes. These bony canals and cavities, like those in the ears of modern burrowing snakes, controlled its hearing and balance.

They built 3D virtual models to compare the inner ears of the fossils with those of modern lizards and snakes. Researchers found a distinctive structure within the of animals that actively burrow, which may help them detect prey and predators. This shape was not present in modern snakes that live in water or above ground.

The findings help scientists fill gaps in the story of snake evolution, and confirm Dinilysia patagonica as the largest burrowing snake ever known. They also offer clues about a hypothetical ancestral species from which all modern snakes descended, which was likely a burrower.

The study, published in Science Advances, was supported by the Royal Society.

Image and representation of brain case and inner ear of Dinilysia patagonica fossil, which scientists at the University of Edinburgh and American Museum of Natural History have used to show that modern snakes lost their legs when their ancestors became expert burrowers. Credit: Hongyu Yi

Dr Hongyu Yi, of the University of Edinburgh's School of GeoSciences, who led the research, said: "How lost their legs has long been a mystery to scientists, but it seems that this happened when their ancestors became adept at burrowing. The inner ears of fossils can reveal a remarkable amount of information, and are very useful when the exterior of fossils are too damaged or fragile to examine."

Mark Norell, of the American Museum of Natural History, who took part in the study, said: "This discovery would not have been possible a decade ago - CT scanning has revolutionised how we can study ancient animals. We hope similar studies can shed light on the evolution of more species, including lizards, crocodiles and turtles."

The video will load shortly
Movie showing the location of the inner ear in a 90-million-year-old fossil of the Dinilysia patagonica snake. The ancient specimen is helping scientists at the University of Edinburgh and American Museum of Natural History discover that modern snakes lost their legs when their ancestors became expert burrowers. Credit: Hongyu Yi

Explore further: Four-legged fossil suggests snakes evolved from burrowing ancestors

More information: The burrowing origin of modern snakes, Science Advances, DOI: 10.1126/sciadv.1500743

Related Stories

Are the blueprints for limbs encoded in the snake genome?

October 1, 2015

Hundreds of millions of years ago, a common ancestor of mammals, birds, and reptiles evolved a phallus. We don't know much about phallus evolution (external genitalia generally don't mineralize, so the fossil record is of ...

Recommended for you

Amber specimen offers rare glimpse of feathered dinosaur tail

December 8, 2016

Researchers have discovered a dinosaur tail complete with its feathers trapped in a piece of amber. The finding reported in Current Biology on December 8 helps to fill in details of the dinosaurs' feather structure and evolution, ...

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

BartV
1.4 / 5 (10) Nov 28, 2015
If you are an evolutionist, then indeed these things are puzzling.

The findings help scientists fill gaps in the story of evolution....


Those scientists better start working a bit harder, because there are billions of "missing gaps" in evolution that no one has found yet.

Dug
not rated yet Nov 28, 2015
Not a very convincing argument unless can define the superior mechanical benefits of the inner ear differences in "burrowing." You also have to understand that few modern snakes are burrowers, but most species utilize the burrows of other animals.

Additionally, burrowing demonstrably favors developing specialized legs (rather than losing them) for excavation as opposed to serpentine locomotion adaptations. Consider moles, tortoises, badgers, rabbits, badgers, etc. and note the commonality of appendages used to excavate in a wide variety of active burrowing animals. These are real burrowers, not snakes that only opportunistically in habit other animals burrows.
Vietvet
4.4 / 5 (7) Nov 28, 2015
@Dug

There are many more species of burrowing snakes than I realized before reading the paper and doing a Google search. I'd suggest reading the paper, it's open access.

http://advances.s...743.full
SuperThunder
4.4 / 5 (7) Nov 28, 2015
According to the Creation Museum, snakes had legs and were called dragons/dinosaurs, but Saint George killed the last one a few hundred years ago, so now we just have lesser cursed dragons with no legs. They're cursed because of the garden of eden, of course, since dragonsaurus liked convincing women to eat apples. While Creation Science Truthilifeyness is unsure of how God can curse snake legs away and still have dragons up and through the divine right of kings, they are absolutely certain there is no contradiction, and that you're all going to hell for giggling.
Multivac jr_
5 / 5 (4) Nov 30, 2015
If you are an evolutionist, then indeed these things are puzzling.

The findings help scientists fill gaps in the story of evolution....


Those scientists better start working a bit harder, because there are billions of "missing gaps" in evolution that no one has found yet.



Well thats patently absurd. It would seem that you don't actually understand Evolution well enough to be against it.
PhotonX
5 / 5 (5) Nov 30, 2015
Those scientists better start working a bit harder, because there are billions of "missing gaps" in evolution that no one has found yet.
Interesting you should put "missing gaps" into quotes, because that's what I was going to do, signifying that they are only so-called "missing gaps". Every time a 'gap' is 'filled', the number of 'gaps' doubles, so there will never be anything other than a vast number of them. It's intellectually dishonest of you to suggest that is somehow a flaw. Do you think we can't recognize a straw man argument when we see one?
.
.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.