The secret behind snakes’ evolutionary success is speed

An orange and yellow coloured snake eating a batch of gelatinous tree frog eggs
A blunt-headed tree snake (Imantodes inornatus) eating its way through a batch of tree frog eggs. Image credit: John David Curlis, University of Michigan
February 25, 2024
Cosmos Magazine

Cosmos

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By Cosmos

A new study has uncovered what triggered the evolutionary explosion of snake diversity – a phenomenon known as adaptive radiation – that led to the nearly 4,000 living species today.

The genetic and dietary study of snakes published in Science suggests that the speed of snake evolution is the answer – up to 3 times faster than lizards.

Snakes and lizards represent the largest order of reptiles, known as Squamata, that make up nearly a third of all land-based vertebrates.

The ancestors of the first snakes were small lizards, but a pulse of evolutionary innovation occurred roughly 128 million years ago that allowed snakes to evolve an incredible range of traits and specialisations.

A ct scan of a snake reveals its skeleton in grey, as well as the blue skeleton of a frog its eaten
f10-CAT-scan.jpg: CT scan of a cat-eyed snake (Leptodeira septentrionalis) reveals a frog (blue skeleton) in its digestive tract. Snake specimen from U-M’s Museum of Zoology. Credit: Ramon Nagesan, University of Michigan Museum of Zoology.

Those changes – such as legless bodies; chemical detection systems to find and track prey; and flexible skulls that enabled them to swallow large animals – led to a spectacular diversification of snakes over the past 66 million years.

“Fundamentally, this study is about what makes an evolutionary winner. We found that snakes have been evolving faster than lizards in some important ways, and this speed of evolution has let them take advantage of new opportunities that other lizards could not,” says Daniel Rabosky, evolutionary biologist at the University of Michigan in the US and senior author of the paper.

“Snakes evolved faster and – dare we say it – better than some other groups. They are versatile and flexible and able to specialise on prey that other groups cannot use.”

The team generated the comprehensive evolutionary tree of snakes and lizards by sequencing partial genomes for nearly 1,000 species. They also compiled a dataset of lizard and snake diets by examining records of stomach contents from preserved museum specimens. 

A graph of diets of lizard and snake species showing the diversity in their food types.
Visualisation of diets for 1,314 species of lizards and snakes. Each point is an individual species: lizards = blue, snakes = red. Points that are closer together indicate greater similarity in diets. The size of each point is proportional to the diversity of food types that each species will eat: Small circles indicate highly specialized diets, for example. Lizards and snakes show very little overlap: Lizards feed largely on insects, spiders and other arthropods. Snakes generally eat frogs, fishes, mammals, birds, and other vertebrates. Credit: Title et al. in Science, February 2024.

By analysing the history of snake and lizard evolution through geological time with models they could then study how various traits evolved.

“One of our key results is that snakes underwent a profound shift in feeding ecology that completely separates them from other reptiles,” Rabosky says.

“If there is an animal that can be eaten, it’s likely that some snake, somewhere, has evolved the ability to eat it.”

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