Study Reveals Snakes Are an Evolutionary Winner

A burst in serpentine form and function reshaped vertebrate diversity

A study of more than 60,000 museum specimens of snakes and lizards worldwide reveals that snakes stand out alone in the evolution of reptiles. The team of scientists, including Stony Brook University’s Pascal Title, discovered by way of assessing the diet and morphology of snakes and genomic data that snakes evolved incredibly fast, as their ancestors shed limbs and adapted on multiple levels to live and thrive and spread out into thousands of species of snakes over 66 million years, up to today. The study will be published in Science this week.

The team of international scientists, led by the University of Michigan, explain that a “burst of innovation in form and function” enabled the ancestors of snakes to move with legless bodies, develop chemical detection systems to find and track prey, and grow flexible skulls to swallow large animals. The changes set the stage for snake diversification and survival, particularly after an asteroid impact wiped out about three-quarters of Earth’s plant and animal species.

“Snakes appear to evolve faster than most other groups of lizards, and our study shows this remarkable concerted ‘acceleration’ in evolutionary tempo across many aspects of snake ecology,” says Title, an assistant professor in the Department of Ecology and Evolution at Stony Brook, and co-lead author of the study. “Snakes are like the Big Bang ‘singularity’ in cosmology — a dramatic expansion of diversity in species and their ecologies, linked to some event that might have occurred early in the evolutionary history of snakes.”

For the study, researchers generated the largest, most comprehensive evolutionary tree of snakes and lizards by sequencing partial genomes for nearly 1,000 species. In addition, they compiled a massive dataset on lizard and snake diets, examining records of stomach contents from tens of thousands of preserved museum specimens.

They quantified macroevolutionary dynamics across a range of ecological, morphological and environmental traits, such as body elongation, venom delivery and vertebral count. The traits were collated from a variety of sources and augmented with primary natural history data from both field- and museum-based research programs. They also took all of the collected specimen data and ran massive statistical comparisons among the thousands of snakes and lizards.

“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,” summarizes University of Michigan evolutionary biologist Daniel Rabosky, senior author of the paper.

Despite the fact that some lizards evolved traits similar to snakes such as venom and limblessness, snakes underwent a profound shift in feeding ecology that completely separates them from other reptiles, adds Title. The evolutionary explosion of snake diversity — a phenomenon known as an adaptive radiation — led to nearly 4,000 living species and made snakes one of evolution’s biggest success stories.

The authors note that the ultimate causes, or triggers, of adaptive radiations is a major mystery in biology. In the case of snakes, it’s likely there were multiple contributing factors, and it may never be possible to fully define each factor and their role in this unique evolutionary process.

The study was supported by several funding agencies, including multiple grants from the U.S. National Science Foundation.

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