Contrary to previous understanding, lizards and snakes were nearly wiped out along with the dinosaurs 65 million years ago, say researchers.
Paleontologist Dr. Nicholas Longrich, of Yale University, and his colleagues report their findings today in the Proceedings of the National Academy of Sciences.
"The dinosaurs were wiped out entirely, but just because lizards and snakes survived, it doesn't mean they weren't affected," said Longrich.
"This is a group that was thought to have been spared the brunt of the extinction and we're showing they were devastated." About 65 million years ago, the dinosaurs were wiped out paving the way for mammals to become the dominant animals on land.
Scientists have debated for some time over what caused the mass extinction, but this study adds to mounting evidence that an asteroid smashing into Chicxulub, Mexico, was to blame, Longrich said.
Previous research had concluded all the major groups of snakes and lizards survived the mass extinction, which occurred at the end of the Cretaceous, but Longrich and colleagues say this finding is an artifact of how different species were classified.
"It's [due to] a geological book-keeping error," said Longrich.
By reclassifying snake and lizard fossils from North America, and including some fossils that had not been previously studied, he and colleagues showed 85 per cent of lizard and snake species went extinct.
"The main implication is that the extinction was more severe than we thought," said Longrich.
He said the findings also fit with the asteroid hypothesis.
"We get an extremely diverse fauna of lizards up until the very end of the Cretaceous, when the asteroid hits," said Longrich.
"Our research strongly supports the idea that the asteroid caused the extinction."
Longrich and colleagues showed many different lineages of snakes and lizards went extinct.
In particular they found animals with certain body plans, lifestyles and ecological niches suffered badly.
"We found the larger you were, the less likely you were to survive," said Longrich, adding the largest snake or lizard to survive the extinction weighed only about 500 grams.
He says it took about 10 million years for lizards and snakes to recover anything like their Cretaceous diversity.
One theory why the smaller creatures stood a better chance of survival during the mass extinction is based on the idea that the asteroid shut out the sunlight and caused a collapse in the food chain.
Plants didn't produce leaves so there wasn't much for herbivores to eat, and without herbivores there wasn't much for big lizards and snakes to eat, said Longrich.
But, there was a build up of dead plant and animal material, which probably boosted the number of insects eaten by smaller insectivorous animals.
"That's my best guess as to what happened," said Longrich.