These Lizards Mysteriously Survived the Asteroid Strike That Killed the Dinosaurs—and Their Descendants Are Still Alive Today
Small and elusive night lizards probably persisted because they have slow metabolisms and like to hide out in rock crevices, a new study suggests
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When the 7.5-mile-wide Chicxulub asteroid smashed into Earth 66 million years ago, it killed most living creatures within hundreds of miles of the impact site. In the chaotic aftermath of the strike, roughly 75 percent of all species worldwide went extinct, including the non-avian dinosaurs.
Yet, somehow, a group of lizards living near the collision point managed to survive not only the initial disaster, but also the ensuing fallout, as researchers report Wednesday in Biology Letters. This makes the reptiles “unique among living families of terrestrial vertebrates,” as they are the only one known to have survived this mass extinction event while living “in close proximity to the impact location,” the team writes in the paper.
Night lizards (Xantusiidae) are a family of small, elusive reptiles that spend most of their time hiding in crevices and under rocks. Today, they’re found in Mexico, Central America, Cuba, California and the southwestern United States.
Researchers knew the night lizard lineage has been around a long time—likely tens of millions of years. But they wanted to get a more precise understanding of the group’s timeline.
Using previously published DNA sequence data, scientists created an evolutionary family tree for night lizards. By studying their mutations over time, the team was able to estimate when the lizards evolved.
Their analyses suggest the most recent common ancestor of living night lizards arose more than 92 million years ago, long before the Chicxulub asteroid crashed down. The creatures have been living in North America and Central America ever since, which suggests at least some of them survived the strike.
Researchers have discovered fossils that seem to support this finding, and the team considered these for the new work. The lizards appear to have lived all around the asteroid impact site, which formed a crater on the Yucatán Peninsula in Mexico and off its coast.
“The fossil record of xantusiids is pretty much fairly continuous on either side of the boundary layer marking the impact,” says lead author Chase Brownstein, an evolutionary biologist at Yale University, to New Scientist’s James Woodford. “It’s almost as if xantusiid distribution sketches a circle around the impact site.”
Fun fact: Extinction of dinosaurs
In the 1980s, scientists discovered a layer of rock that’s oddly rich in the metal iridium across the planet. While iridium is rare on Earth, it’s common in some asteroids, so this finding offered scientists a key piece of evidence that an asteroid impact led to the extinction of non-avian dinosaurs.
Based on their research, the scientists say at least two distinct night lizard lineages outlived the asteroid collision. One lineage gave rise to the Xantusia genus, which today includes more than a dozen living species found in California, the southwestern U.S. and Mexico’s Baja Peninsula, as well as the Lepidophyma genus, which currently lives in North and Central America. The other lineage led to the Cricosaura genus, consisting of one living species—Cricosaura typica—found in Cuba today, per Live Science’s Patrick Pester.
But how did night lizards survive while most other animals perished? Scientists don’t know for certain, but they suspect the reptiles were able to ride out the disaster because of their slow metabolism and preferred habitats. They might have been able to hunker down—without needing to head out in search of food—during and after the collision.
Night lizards were not the only creatures to survive the asteroid-induced mass extinction event. Some birds, turtles, snakes, fish and mammals persisted, which helped give rise to the numerous species alive today. However, many of these ancestral lineages eventually died out, while night lizards endured. They have continued living in the same general area—North America and Central America—through to the present day.
“The problem is that [other animals] just aren’t there anymore,” Brownstein tells Live Science. “So, what’s interesting is that xantusiids have persisted and have remained endemic to the region.”
The study produced another intriguing finding: Ancestral night lizards had very small litter sizes, probably consisting of just one or two offspring. That’s surprising, because animals that survive mass extinction events tend to reproduce quickly, as Nathan Lo, an evolutionary biologist at the University of Sydney who was not involved with the research, tells New Scientist.
Night lizards also had a fairly small geographic range—another characteristic that should have made it difficult for them to persist after the asteroid strike, Lo adds.
For now, much of the night lizard’s survival story remains a mystery—and potential fodder for future research. The fact that these little reptiles managed to endure “further complicates our understanding of extinction survival mechanisms,” researchers write in the paper.
