An Evolutionary ‘Big Bang’ Explains Why Snakes Come in So Many Strange Varieties

An evolutionary ‘big bang’ explains why snakes exist in so many strange taxa

Written by Jack Tamesiya Edited by Andrea Thompson

When snakes first evolved from lizards more than 100 million years ago, they were ecological players slithering around the edges of dinosaur-dominated ecosystems. But today there are about 4,000 species of snakes, ranging in size from green anacondas that weigh more than an adult gorilla to thread snakes that are lighter than a paper clip. They are some of the most effective and diverse predators on Earth. “Snakes are really exceptional,” says Daniel Rabosky, an evolutionary biologist at the University of Michigan.

Of the approximately 25 groups of lizards that have independently lost their legs, snakes are the only group that is truly exploding in diversity. A new study published this week in sciences Explains why: Genomic data has revealed this Snakes experienced a wave of adaptation about 125 million years ago— early in their evolutionary history — which helped them exploit multiple ecological gaps. “The research shows that snakes are an evolutionary ‘singularity’ that changed the face of the Earth,” says Michael Lee, an evolutionary biologist at Flinders University in Australia, who studies the evolution of reptiles but was not involved in the new research.

To determine what distinguishes snakes from groups of legless lizards, Rabosky and a team of researchers built an in-depth evolutionary tree. They modeled their clades using genomic data from more than 1,000 species of squamates (the order of reptiles that includes snakes and lizards) to chart how these scaly creatures changed over time. Finally, they augmented this dataset with nutritional information from nearly 70,000 individual lizards and snakes, primarily specimens preserved in alcohol in museum collections.

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The results showed a wave of early adaptation that appears to be linked to the evolution of specialized traits. These features include chemoreceptor structures that help snakes expertly locate their prey using scent and heat, and flexible jaws that help them swallow larger meals. Some snakes have developed deadly venom to hunt larger prey.

The new paper did not go out on a limb to determine the specific trait that led to the snakes’ success. Maybe it was the interaction between traits that helped them hit the evolutionary jackpot, Lee says. “Snakes succeed because of the synergy of multiple adaptations [such as] “Elongated bodies, constriction, venom, and flexible skulls,” he tells me. “Many legless lizards have one or two of these snake traits but are not nearly as successful.” He cites a group of geckos that have an elongated body and flexible skull but have never diversified into more than a handful of species.

Rabosky agrees that the adoption of a set of specialized traits likely helped fuel the evolution of snakes. Based on the study’s evolutionary tree, it appears that snakes evolved up to three times faster than lizards. “The rate at which snakes evolve new features and develop new types of diets has been kicked into overdrive,” Rabosky says. “Lizards ride around on a motorcycle while snakes are on a bullet train.”

This rapid evolution likely allowed snakes to exploit more ecological gaps than lizards after the catastrophic mass extinction that occurred 66 million years ago, which wiped out several groups of reptiles, including non-avian dinosaurs. This diversity is still reflected in the diet of snakes today. Most living lizards attach themselves to insects or other small arthropods; Snakes are usually more adventurous and will prey on animals ranging from rodents and birds to kangaroos and crocodiles.

Although snakes have collectively evolved diverse tastes, many species are highly specialized in targeting specific prey. These include species of shovel-nosed snakes, which have evolved to burrow into their prey, and species of sea snakes, which swim with a paddle-like tail and snack on prey such as reef fish. Other species swallow bird eggs whole. Some even consume harmful food that only a few other species would dare to eat. Most lizards are much less specialized and simply eat any invertebrates small enough to fit in their mouths.

Rabosky and his colleagues describe the wave of evolutionary innovation that led to the evolution of snakes as a “major evolutionary singularity.” Like the evolutionary Big Bang, these rare events occur when a group of organisms rapidly diversifies into a variety of new species in the blink of an eye, by geological standards. The sudden explosion in the diversity of flowering plants during the Cretaceous period is another example of this phenomenon, which Charles Darwin called the “abominable mystery.”

It’s just another example of how important “the Big Bang of evolution has been in the history of life on Earth,” Rabosky says.