Every species of bird is descended from an emu-like ancestor which survived the meteor strike that killed off the dinosaurs, scientists believe.
The cataclysm 66 million years ago wiped out Tyrannosaurus rex and other dinosaurs – but also killed off all flying birds.
As forests burned around the world only flightless species that lived on the ground survived.
It means that all modern species of birds have a common ancestor, whose descendants had to learn to fly again over generations, suggest the scientists.
All birds are said to be from an emu-like bird which could not fly. But birds learnt to take to the skies again over the generations
British co-author Dr Daniel Field, from the University of Bath, said: ‘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.
‘The ancestors of modern tree-dwelling birds did not move into the trees until the forests had recovered from the extinction-causing asteroid.’
Dr Regan Dunn, another member of the internationsl team from the Field Museum in Chicago, U.S., 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 extinction of the dinosaurs is believed to have been triggered by an asteroid or comet – six to nine miles wide – which struck the Earth off the coast of Mexico.
All birds share a common ancestor, according to scientists, who have said the non-flying bird was like an emu
It released 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.