A yellow-spotted tropical night lizard (Lepidophyma flavimaculatum)
Image courtesy of Dante Fenolio/Science Photo Library
Joel Kontinen
Lizards are not dinosaurs. but somehow the dinosaur eating catastrophe that happened some 66 million years old did not affect these lizards. They may have been present some 66 million years ago.
The night lizards
may have been the only terrestrial vertebrates that survived in the region of
the asteroid impact 66 million years ago, which led to the extinction of
non-avian dinosaurs
A small, secretive
group of lizards that still exists today may have been the only terrestrial
vertebrates that survived in the vicinity of the Chicxulub asteroid collision, which led to the extinction of the non-avian dinosaurs.
It has long been
known that xantusiid night lizards are an ancient lineage that have persisted
for tens of millions of years. But Chase Brownstein at Yale
University and his colleagues suspected that the group may have actually arisen
earlier than previously thought: in the Cretaceous Period, which ended around
66 million years ago.
The end of the
Cretaceous was marked by a giant asteroid strike in the vicinity of Yucatán
peninsula in Mexico, which left a crater over 150 kilometres wide and caused
the extinction of most of the animal and plant species across the world.
Brownstein and his
team used previously published DNA sequence data for xantusiids to create an
evolutionary tree for the group. They combined this with skeletal anatomy
across living and fossil night lizards, allowing the team to determine how old
their lineages are and estimate how many offspring the ancestral night lizards
would have produced.
They found that
the most recent common ancestor of living xantusiids emerged deep within the
Cretaceous, over 93 million years ago, and they probably only had clutches of
one or two offspring.
“I think it is
very possible that these ancient populations were as close or closer to the
impact site than those today,” says Brownstein. “It’s almost as if xantusiid
distribution sketches a circle around the impact site.”
Based on fossil
evidence, it is unlikely that the ancient night lizards simply recolonised the
region later on, says Brownstein.
“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,” he
says.
Many night lizard
species live in rock crevices and their slow metabolisms are comparable to
those of other survivors of the mass extinction, such as turtles and
crocodiles. “This, perhaps, would have allowed them to take shelter during the
impact and its immediate aftermath,” says Brownstein.
Nathan Lo at the University of Sydney says the
lizards are remarkable. “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 kilometres of the impact
point.”
They managed this
despite not having many of the usual traits that we would expect to see in
survivors of mass extinctions. “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,” says Lo. “But these lizards generally reproduce
slowly and seem to have quite small ranges.”
James Woodford 2025
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