After dinosaurs, Earth became an all-you-can-eat buffet for snakes

When it comes to snakes, the modern world offers an embarrassment of riches. Today there are nearly 4,000 different snake species, placing the group not far behind mammals in terms of diversity. Snakes are also diverse in the types of food they prefer to consume – some will feast on earthworms only, while others can swallow a deer whole.

“They just have an amazing variety of diets,” says Michael Grundler, postdoctoral researcher in ecology and evolutionary biology at the University of California, Los Angeles. He and his colleague Daniel Rabosky from the University of Michigan wanted to know how this group had become so diverse and successful.

When they analyzed both the diets and evolutionary relationships between hundreds of current snakes, the couple found that the mass extinction that ended the dinosaurs was a game-changer for limeless reptiles. The first snakes crept into newly vacant ecological niches and quickly developed their ability to prey on a wide range of prey, the scientists reported on Oct. 14 in the newspaper. PLOS Biology.

Little is known about the early chapters in the evolution of snakes, as animals are rarely preserved in fossil form, Grundler explains. So he and Rabosky used information from living species to probe their history. They gathered more than 34,000 reports on the diets of 882 species based on observations of wild snakes and dissected museum specimens. The researchers also relied on family trees determined from the genetics of modern snakes.

“With these two pieces of information, we can make inferences about what extinct species might have looked like a long time ago,” says Grundler. The team used mathematical models to reconstruct how quickly these ancestral snakes might have changed over time as their diets changed.

The first snakes were probably insectivores. However, by the time the dinosaur-killer asteroid arrived 66 million years ago, they had branched out a bit to dine on vertebrate prey.

“Shortly after this event, we find the signal for a big explosion in dietary diversity,” Grundler said. “The survivors of this event developed this vast array of eating styles that we see today.”

After this explosion of activity, many groups also changed their diets very quickly when they moved to new places. A particularly striking example is that of the dipsadine snakes, a subfamily of over 700 species that includes the Eastern Hound Snakes and False Coral Snakes. After arriving in South America, “they simply exploded in their dietary diversity in a relatively short period of time,” says Grundler. “They evolved to specialize in earthworms, fish, frogs, slugs, eels, and even other snakes.”

[Related: These snakes wiggle up smooth poles by turning their bodies into ‘lassoes’]

In contrast, some groups of snakes evolved much more slowly. Blind snakes, which feed primarily on colonial insects like ants and termites, appear to have had similar diets for tens of millions of years, says Grundler.

The findings highlight how opportunities such as the disappearance of hungry competitors (and the rise of rodents and other delicacies) and the establishment of new habitats “are shaping changing fortunes,” he adds.

For snakes, this has led to a spectacular collection of adaptations for eating on mammals, birds, fish, amphibians, other reptiles, and a multitude of invertebrates. The emergence of the venom allowed vipers and other ambitious snakes to take down prey that might otherwise be too dangerous to control.

There were also more unusual developments; members of the Southeast Asian Pareinae subfamily that eat snails exclusively have more teeth on one side of the jaw than on the other. This makes it easier for the snakes to “enter and rake the body of the snail” to extract the hapless animal from its asymmetrical shell, Grundler explains.

At the same time, he and Rabosky observed, even snakes apparently specialized for one type of prey are known to gobble up other animals that come their way. This ability to eat adventurously may have helped early snakes to innovate and thrive throughout their history.

While the new analysis covers all major snake families, Grundler says, it only includes about a quarter of known species. “There are thousands of species of snakes that we know very little about,” he says. “We still have a long way to go.”

The next step will be to gather more information about these mysterious snakes and to research more information on the remains of their missing loved ones.

“This [work] it’s all about living species, ”says Grundler. “If we are able to get better observations on the diet of fossil snakes and include them in our analysis, that would be really important.”

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