About 128 million years ago, a surge of adaptation caused snakes to explode in diversity and evolve up to three times faster than lizards.
Since they initially descended from lizards, snakes were minor ecological players that slithered around the periphery of ecosystems dominated by dinosaurs more than 100 million years ago. But now, there are roughly 4,000 distinct species of snakes. They range in size from green anacondas that weigh more than grown gorillas to thread snakes that are as light as a paperclip. These are some of the planet’s most successful and diverse predators. According to University of Michigan evolutionary scientist Daniel Rabosky, snakes are “truly exceptional.”
Snakes were the only lizard families to experience a true explosion in variation out of the roughly twenty-five that lost their legs individually. A fresh study that was published this week in Science explains why this is the case. Based on available genome data, the snake species underwent a rapid adaptive change approximately 125 million years ago, which enabled them to exploit many ecological openings. “The paper demonstrates that snakes are an evolutionary “singularity” that has changed the face of the Earth,” claims Michael Lee, an evolutionary biologist at Flinders University in Australia who specializes in the evolution of reptiles but was not involved in the current research.
To find out what set snakes apart from groups of limbless lizards, Rabosky and associates constructed an extensive evolutionary tree. They formed its branches by illuminating the evolutionary history of these scaly critters, which includes snakes and lizards, using genomic data from over 1,000 species of squamates (the order of reptiles). Finally, they included feeding data from almost 70,000 different snakes and lizards to this dataset, most of which were specimens housed in alcohol that were part of museum collections.
The results showed an early surge of adaptation that was linked to the formation of specialized traits. These features include chemoreceptive organs that allow snakes to precisely detect their prey by scent and heat, and flexible jaws that allow them to swallow huge meals. Certain snakes have evolved deadly venom to hunt larger prey.
The present study refrains from speculating as to what specific trait made snakes successful. Lee thinks a mix of qualities most likely contributed to their evolutionary success. According to Lee, “A combination of various adaptations, including elongated bodies, constriction, venom, and flexible skulls, contribute to the success of snakes,” Many legless lizards haven’t been nearly as successful, even when they possess one or two of these snake characteristics. He talks of a class of geckos that only numbered a few species; they featured an expanded body and a flexible skull.
Rabosky agrees that the adoption of several specialized traits by snakes likely sped up their evolutionary process. The evolutionary tree presented in the study suggests that snake evolution happened up to three times quicker than lizard evolution. Rabosky claims that there has been a discernible increase in the rate at which snakes are developing new traits and diets. “While snakes are traveling on a bullet train, lizards are stumbling around on a moped.”
Given their quick evolution, snakes were likely able to take advantage of more ecological gaps than lizards following the catastrophic mass extinction that wiped off multiple reptile groups 66 million years ago, including the non-avian dinosaurs. Even now, snake diets show this versatility. Living lizards often consume insects or other small arthropods, while snakes are much braver and will consume everything, including rodents, birds, kangaroos, and crocodiles.
Although snakes have collectively evolved varied tastes, many species are highly specialized to target specific prey. These include species of shovel-nosed snakes, which evolved to dig up prey, and species of sea snakes, such as reef fish, which swim with a paddlelike tail and snack on prey. Other species swallow bird eggs whole. Some even consume noxious fare that few other species would dare eat. Most lizards specialize far less and eat whatever invertebrates are small enough to fit in their mouth.
Rabosky and his co-authors describe evolutionary innovation that kick-started snake evolution as a “macroevolutionary singularity.” Like an 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 of flowering plant diversity during the Cretaceous period is another example of this phenomenon, which Charles Darwin called an “abominable mystery.”
It’s just one more example, Rabosky says, of how “these big bangs of evolution are profoundly important to the history of life on Earth.”
The following is based upon
Tamisiea J. 2024. An Evolutionary ‘Big Bang’ Explains Why Snakes Come in So Many Strange Varieties. Scientific American, February 23, 2024.
Title PO, et al. 2024. The macroevolutionary singularity of snakes. Science 383(6685): 918-923.
