The Enigmatic Lizard: Surviving the Chicxulub Asteroid Impact

A unique and elusive group of lizards remains today, recognized as the only terrestrial vertebrates to withstand the catastrophic Chicxulub asteroid impact, which likely resulted in the extinction of non-avian dinosaurs.

The Xantusiid Night lizard is known as an ancient lineage, surviving for tens of millions of years. However, Chase Brownstein from Yale University and his team proposed that this lineage might have originated earlier than previously estimated.

The end of the Cretaceous period was marked by a colossal asteroid strike near the Yucatán Peninsula in Mexico, creating craters wider than 150 kilometers and leading to the extinction of most animal and plant species globally.

Today, the night lizard—despite its name, not actually nocturnal—continues to inhabit Cuba, Central America, and the southwest region of the United States.

Brownstein and his researchers utilized previously published DNA sequencing data from Xantusiids to construct evolutionary trees for these groups. They integrated findings from skeletal anatomy of current species and fossil records, allowing them to estimate the lineage’s age and the quantity of offspring produced by the ancestral night lizard.

The team identified a shared ancestor that lived deep within the Cretaceous period, dating back over 93 million years, likely producing only one or two clutches of offspring.

“It’s highly probable that these ancient populations were situated close to the impact site, much like their modern counterparts,” remarks Brownstein. “It’s as though the distribution of Xantusiid lizards encircles the impact zones.”

According to fossil records, Brownstein argues that it is improbable for ancient night lizards to have simply returned to the affected areas later.

“Our reconstructions suggest that the common ancestors of living species most likely originated in North America, as the fossil evidence of Xantusiids is relatively continuous on both sides of the boundary layer,” he adds.

Numerous night lizard species inhabit rock crevices and possess a slow metabolism akin to other survivors of mass extinction, like turtles and crocodiles. “This likely enabled them to endure the aftermath of the impact,” states Brownstein.

Nathan Law from the University of Sydney expresses amazement at their survival. “These lizards resided near the asteroid’s impact site; despite the asteroid’s devastating effects within hundreds of kilometers, they managed to survive.”

Remarkably, they achieved this despite lacking many common characteristics typically associated with mass extinction survivors. “Species that endure these extinction events tend to be small, reproduce rapidly, and have extensive geographical ranges,” explains Law. “Conversely, these lizards generally have slower reproduction rates and appear to cover a minimal range.”