Dinosaurs

he 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," says 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 this mass extinction, but says Longrich, this study adds to mounting evidence that an asteroid smashing into Chicxulub, Mexico, was to blame.

Book-keeping error -

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 artefact of how different species were classified.

"It’s [due to] a geological book-keeping error," says 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," says Longrich.

He says 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," says Longrich.

"Our research strongly supports the idea that the asteroid caused the extinction."

Smaller animals survived -

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," says 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.

Collapse of food chain -

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, says 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.