A night lizards of the family Xantusiidae survived the giant asteroid strike that ended the reign of the dinosaurs 66 million years ago near the epicenter of the impact. Remarkably, these reptiles continue to inhabit the same regions of North and Central America today. The findings were published in the journal Biology Letters.
A new evolutionary analysis discovered that night lizards were living around the Gulf of Mexico before and after the asteroid struck what is now Mexico's Yucatán Peninsula. These lizards continue to thrive around the Gulf of Mexico and farther south in southern Central America.
Night lizards are the only group of land vertebrates known to have survived close to the impact location of the asteroid and still have members living in the region today. This makes them unique among terrestrial vertebrates, as they have persisted in the same area since the catastrophe that caused the extinction of around 75% of all species.
These small reptiles, which grow to only a few inches in length, inhabit specialized microhabitats such as crevices in rocks and under tree bark. They are often secretive, a trait that may have contributed to their survival during the mass extinction event.
Two lineages of night lizards managed to persist through the disaster near the epicenter of the impact on the Yucatán Peninsula, where the 180-kilometer Chicxulub crater is located today. One lineage gave rise to the genus Xantusia, which ranges from the southwestern United States into Mexico, and to the genus Lepidophyma, which ranges across parts of North America and Central America. The second lineage gave rise to the genus Cricosaura and its only species, Cuban night lizards (Cricosaura typica), in Cuba.
Using molecular clock dating, the researchers estimated that the most recent common ancestor of living night lizards emerged deep within the Cretaceous period, around 90 million years ago. This suggests that night lizards have been living in North America and Central America well before the asteroid struck and have persisted there ever since.
Despite the widespread devastation caused by the asteroid, night lizards managed to survive, even though they lack many of the traits typically associated with survivors of mass extinctions. Researchers aren't sure how these reptiles endured amid all the devastation. Their survival remains a mystery, but scientists suggest that a slow metabolism and a secretive lifestyle played a key role.
Chase Brownstein noted that some lineages of turtles and other lizards in the region probably survived the asteroid in a similar way as night lizards did. "It's almost as if xantusiid distribution sketches a circle around the impact site," he said, according to New Scientist.
Based on fossil evidence, it is unlikely that the ancient night lizards simply recolonized the region later on. "We know from our reconstructions that the common ancestor of living species was almost certainly living in North America, where the fossil record of xantusiids is pretty much fairly continuous on either side of the boundary layer marking the impact," Brownstein explained.
Nathan Lo at the University of Sydney commented on the resilience of these lizards. "They lived in the region around the asteroid's point of impact, yet they managed to survive, even though the asteroid would have wiped out organisms that were within hundreds of kilometers of the impact point," he said.
Night lizards' slow metabolisms are comparable to those of other survivors of the mass extinction, such as turtles and crocodiles. However, unlike typical survivors that tend to be small in size, reproduce quickly, and have large geographic ranges, night lizards generally reproduce slowly and seem to have quite small ranges.
"The species that tend to survive through these extinction events are those that are small in size, reproduce quickly, and that have large geographic ranges," Lo noted. "But these lizards generally reproduce slowly and seem to have quite small ranges."
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