Tail shortening enabled birds to develop versatile legs 100 mn yrs ago
Washington: A new study has claimed that radical shortening of bird`s bony tails, over 100 million years ago, enabled them to develop versatile legs, which gave them an evolutionary edge.
A team led by Oxford University scientists examined fossils of the earliest birds from the Cretaceous Period, 145-66 million years ago, when early birds, such as Confuciusornis, Eoenantiornis, and Hongshanornis, lived alongside their dinosaur kin.
At this point birds had already evolved powered flight, necessitating changes to their forelimbs, and the team investigated how this new lifestyle related to changes in their hind limbs (legs).
The team made detailed measurements of early bird fossils from all over the world including China, North America, and South America. An analysis of this data showed that 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, prefiguring the amazing variety of talons, stilts, and other specialised hind limbs that have helped to make modern birds so successful.
Dr Roger Benson of Oxford University`s Department of Earth Sciences, who led the research, said that 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.
He explained that what surprised them was that despite some still having primitive traits, such as teeth, these early birds displayed an incredibly diverse array of versatile legs.
By comparing measurements of the main parts of the legs of early birds-upper leg, shin, and foot - to those of their dinosaur relatives Dr Benson and co-author Dr Jonah Choiniere of the University of the Witwatersrand, South Africa, were able to determine whether bird leg evolution was exceptional compared to leg evolution in dinosaurs.
Roger said that their study showed 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.
He added that 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.
It was developing these highly versatile legs, rather than powered flight, that saw the evolutionary diversification of early birds proceed faster than was generally true of other dinosaurs.
The research has been published in Proceedings of the Royal Society B.
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