Losing their tails gave early birds an evolutionary leg-up that helped them compete with their dinosaur cousins, research has shown.
Birds only developed a versatile, adaptive range of hind limbs after radical shortening of their bony reptilian tails, according to a fossil study.
The change triggered a burst of evolution that enabled birds to adapt to different habitats and lifestyles 155 to 120 million years ago.
Today they still carry the results of that transformation in the form of talons, tall stilts, perching claws and webbed paddles.
Development of such a different array of legs was a bigger driver of bird evolution than powered flight, scientists believe.
“These early birds were not as sophisticated as the birds we know today,” said study leader Dr Roger Benson, from Oxford University’s Department of Earth Sciences.
“If modern birds have evolved to be like stealth bombers then these were more like biplanes.
“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.”
The team conducted measurements of the legs of ancient birds and their dinosaur relatives to compare their rate of evolution.
Changes occurred faster in the birds, examples of which included Confuciusornis, Eoenantiornis and Hongshanornis.
The findings appear in the journal Proceedings of the Royal Society B.
“Our work shows that, whilst 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,” said Benson.
“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.”