Enigmatic lizards somehow survived near Chicxulub asteroid impact

A small secret group of lizards that still exist today has perhaps been the only terrestrial vertebrates that have survived near the asteroid collision of Chicxulub, which led to the extinction of non-avian dinosaurs.

It has been known for a long time that XANTUSIID night lizards are an old line that persists for tens of millions of years. But Chase Brownstein at the University of Yale and his colleagues suspected that the group may have taken place earlier than before: in Cretaceous, which ended about 66 million years ago.

The end of the Cretaceous was marked by a giant asteroid strike near the Yucatán peninsula in Mexico, which left a crater over 150 kilometers wide and caused the extinction of most animal and plant species around the world.

Today, night lizards – an unfit term because they are not really nocturnal – are still in Cuba, Central America and the Southwest of the United States.

Brownstein and his team used DNA sequence data previously published for XANTUSIIDS to create an evolutionary tree for the group. They combined this with a skeletal anatomy through living and fossil night lizards, allowing the team to determine the age of their lines and estimate how many descendants the ancestral night lizards would have produced.

They found that the most recent common ancestor of the living xantussiids appeared at the bottom of the Cretaceous, more than 93 million years ago, and they probably only had claws of one or two offspring.

“I think it is very possible that these ancient populations are as close or closer to the impact site than those of today,” explains Brownstein. “It is almost as if the distribution of Xantuiid sketches a circle around the impact site.”

Based on fossil evidence, it is unlikely that the old night lizards simply recolonized the region later, explains Brownstein.

“We know by our reconstructions that the common ancestor of living species lived almost certainly in North America, where the fossil file of the XantUsiids is almost quite continuous on each side of the layer bounds up the impact,” he said.

Many species of night lizards live in rocky crevices and their slow metabolisms are comparable to those of other survivors of mass extinction, such as turtles and crocodiles. “This, perhaps, would have allowed them to take refuge during the impact and its immediate consequences,” explains Brownstein.

Nathan Lo at the University of Sydney says that the lizards are remarkable. “They lived in the region around the point of impact of the asteroid, [yet] They managed to survive, even if the asteroid would have destroyed the organisms which were less than hundreds of kilometers from the impact point. »»

They succeeded despite the fact of not having many usual features that we would expect to see the survivors of mass extinctions. “The species which tend to survive through these extinction events are those which are small, reproduce quickly and which have large geographic ranges,” explains Lo. “But these lizards generally reproduce slowly and seem to have fairly small ranges.”