Snakes have managed to live comfortably without limbs for millions of years, but why they evolved to slither rather than walk has remained an ongoing mystery. Competing theories have each pleaded their case based on ancient environments, arguing over whether the first snakes evolved to navigate underwater, on land, or underground.
A new study published in Nature has entered the debate with evidence that could change everything, all based on an 80-million-year-old fossil of an early snake found in Brazil. While this snake had a dense skull suggesting it spent its days burrowing headfirst underground, another ancient snake had features better suited to a surface-dweller.
These opposing lifestyles show that not all early snakes stuck to just one environment — many snakes evolved to settle into different environments.
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Finding a Rare Snake Fossil
Snakes emerged in the Middle Jurassic, around 174 million to 161 million years ago, but the circumstances surrounding their origins remain murky even today. That’s because fossils of the earliest snakes are incredibly scarce; fewer than 10 articulated snake fossils, according to the new study, are known from the Mesozoic (the era that spanned the Triassic, Jurassic, and Cretaceous periods).
This fossil count, however, has now gone up thanks to the discovery of a fossil snake embedded within a roughly 80-million-year-old rock in São Paolo state, Brazil. The species, named Tametara mirim, is exceptionally well-preserved, with its bones still connected in their original arrangement.
A Skull Made for Burrowing
Where T. mirim really stands out, though, is in its head. Researchers examined its skull, finding it to be made of thick and dense bone. These qualities make it similar to head-first burrowing reptiles with skulls built for digging through the ground.
The researchers also used micro-CT scans to reconstruct the snake’s brain cavity. The reduced visual and forebrain structures that they identified reinforced the idea that T. mirim was a burrower (otherwise known as a fossorial species).
But not all early snakes followed the same underground path. The researchers compared T. mirim with another early snake, Dinilysia. They noticed that this snake, originally found in Argentina, had a very different brain from that of T. mirim.
Many burrowing reptiles, including T. mirim, show greater bone compactness, thickness, and skull elongation, according to the researchers.
Non-burrowing reptiles, or ground-dwelling reptiles, have comparatively less compact bones and shorter skulls. Since the skull of Dinilysia displays these traits, it likely lived on the surface.
T. mirim, adapted to life underground, would have also had much worse eyesight than Dinilysia.
Settling the Great Snake Debate
Citing their comparison of the two early snakes, the researchers say that the origins of snakes were not shaped by a single, linear event like adaptation to life underground, on the surface, or in water. Rather, many species of early snakes diverged throughout their evolutionary history, each adapted to its own preferred habitat.
Some Late Cretaceous lineages were burrowing, while others were ground-dwelling, and marine snakes, such as those in the family Simoliophiidae, also branched off.
Today, we envision most snakes slithering on the surface, but some snakes retained the ability to burrow underground, like hognose snakes. There are even sea snakes found in shallow, tropical waters from the eastern Pacific Ocean to the Indian Ocean. These swimming snakes, according to the Natural History Museum in London, tend to hunt in reefs, seagrass meadows, or on the muddy seafloor.
The debate over snake origins, therefore, may best be resolved by looking at the diversity of early snakes, which has carried on to this day.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in Nature: Exceptional brain and ecological diversity in the earliest snakes
- This article references information from the Natural History Museum: A deep dive into sea snakes, sea kraits and their aquatic adaptations