The origin story behind every living snake
Nearly 4,000 snake species are alive today: vipers, cobras, garter snakes, pythons, boas, sea snakes, the garden variety curled up in a hedge. A 2021 study in Nature Communications, led by Dr. Catherine Klein and Nick Longrich with collaborators from the University of Bath, Bristol, Cambridge, and Germany, traced nearly all of that variety back to a small handful of ancestral lineages that survived the asteroid impact that ended the Cretaceous period 66 million years ago, the same event that wiped out the dinosaurs. Plenty of snakes existed before the impact. Almost none of those Cretaceous species made it through.
How a snake happened to be built for exactly this disaster
The asteroid did not just flatten things on impact. It set off extreme heat, wildfires, and a collapse of food chains that starved out anything that had to stay active and keep hunting in the open. Klein, Longrich, and their team argue that snakes already had, by accident, the toolkit for surviving that specific kind of catastrophe: a habit of sheltering below ground, and a physiology built to go long stretches without eating. Neither trait evolved for this moment. Both were already sitting there, unused, until the one event where they mattered more than anything else a reptile could offer.
Surviving was only the setup. The empty world is the story.
Getting through the impact explains why a few lineages made it. It does not explain why there are 4,000 species today instead of a dozen. According to the study, the ancestor of every living snake probably originated somewhere in the Southern Hemisphere, and its descendants, a clade called Afrophidia that today includes most snakes alive, later spread into Asia once the extinction had cleared the field. Fossil snake vertebrae from that window change shape abruptly: old forms disappear, new ones show up, including sea snakes that reached 33 feet (10 m) long, a size and a way of life with no earlier precedent in the group. Klein has called the speed of this the real surprise in the findings: surviving an extinction that erased so much else was only the first part, and doing something genuinely new with habitat within a few million years afterward was the second.
The myth this kills
The easy assumption is that today’s snake diversity is a straight continuation: Cretaceous snakes doing what Cretaceous snakes always did, just with 66 million more years to pile up species. The fossil and genetic record says the opposite. This is a bottleneck followed by a burst, not a smooth climb. Nearly everything was wiped out first, and the diversification only took off once the field was empty. Longrich frames the mechanism as “creative destruction”: removing the old occupants of a niche is what lets survivors move into it. Snakes did not slowly outcompete their Cretaceous relatives over eons. Their relatives were removed all at once, and snakes moved into the vacancy left behind.
What the study still can’t tell you
The paper does not put a number on the “handful” of lineages that made it through, and it does not name them. It does not detail the route or the timing by which the Southern Hemisphere ancestor’s descendants reached Asia. And it flags a second major burst of diversification tied to Earth’s shift from a warm “Greenhouse” climate to a cold “Icehouse” one, marked by the appearance of the first polar ice caps, without attaching a firm date to that shift. Those are named as open questions, not filled in with a guess to make the story feel finished.
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