A team led by Oxford University scientists examined fossils of the earliest birds from the Cretaceous Period, 145 million to 66 million years ago, and found the loss of their long bony tails, which occurred after flight had evolved, led to an explosion of diversity in the hind limbs of early birds.
The change led to the amazing variety of talons, stilts and other specialized hind limbs that have helped make modern birds so successful, they said.
"These early birds were not as sophisticated as the birds we know today -- if modern birds have evolved to be like stealth bombers then these were more like biplanes," Oxford researcher leader Roger Benson said. "Yet what surprised us was that despite some still having primitive traits, such as teeth, these early birds display an incredibly diverse array of versatile legs."
Bird leg evolution was exceptional compared to leg evolution in dinosaurs, he said.
"Our work shows that, [while] they may have started off as just another type of dinosaur, birds quickly made a rather special evolutionary breakthrough that gave them abilities and advantages that their dinosaur cousins didn't have," Benson said in an Oxford release Tuesday. "Key to this special 'birdness' was losing the long bony dinosaur tail -- as soon as this happened it freed up their legs to evolve to become highly versatile and adaptable tools that opened up new ecological niches."
The study has been published in the Proceedings of the Royal Society B.