Birds had to rediscover flight all over again after the meteor strike that killed off the dinosaurs, scientists believe.
The cataclysm 66 million years ago not only wiped out Tyrannosaurus rex and his relatives, but also tree-living flying birds.
As forests burned around the world the only birds to survive were flightless species that lived on the ground.
Every bird alive today is descended from these emu-like ancestors, the scientists believe.
Dr Regan Dunn, a member of the team from the Field Museum in Chicago, US, said: “Looking at the fossil record, at plants and birds, there are multiple lines of evidence suggesting that the forest canopies collapsed.
“Perching birds went extinct because there were no more perches.”
The six to nine-mile-wide meteor, which may have been an asteroid or comet, struck the Earth off the coast of Mexico releasing a million times more energy than the largest atomic bomb.
Hot debris raining from the sky is thought to have triggered global wildfires immediately after the impact.
It took hundreds or even thousands of years for the world’s forests to recover.
Fossil records from New Zealand, Japan, Europe and North America, all showed evidence of mass deforestation.
They also revealed that birds surviving the end of the Cretaceous period had long sturdy legs made for living on the ground. They resembled emus and kiwis, said the researchers whose findings are reported in the journal Current Biology.
British co-author Dr Daniel Field, from the University of Bath, said: “The ancestors of modern tree-dwelling birds did not move into the trees until the forests had recovered from the extinction-causing asteroid.”
Dr Field added: “Today, birds are the most diverse and globally widespread group of terrestrial vertebrate animals – there are nearly 11,000 living species.
“Only a handful of ancestral bird lineages succeeded in surviving the mass extinction event 66 million years ago, and all of today’s amazing living bird diversity can be traced to these ancient survivors.”