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Research shows early birds had bony tails
A research team composed of University of the Witwatersrand senior researcher Dr Jonah Choiniere and Dr Roger Benson of Oxford University's Department of Earth Sciences examined fossils of the earliest birds from the Cretaceous Period (145-66 million years ago). At that time primitive birds such as Confuciusornis had already evolved powered flight while living alongside their dinosaur kin, necessitating changes to their forelimbs. The team investigated how this new aerial lifestyle related to changes in their hind limbs.
The team made detailed measurements of early bird fossils from all over the world including China, North America and South America. An analysis of these data showed that the loss of their long bony tails, which occurred after flight had evolved, prefigured the amazing variety of talons, stilts, and other specialised hind limbs that make modern birds so successful. The research was recently published in the prestigious journal Proceedings of the Royal Society B.
Determining leg evolution
"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," said Dr Benson, who led the research. "Yet despite some still having primitive traits, such as teeth, these early birds still display an incredible array of leg shapes."
By comparing measurements of the main parts of the legs of early birds - upper leg, shin, and foot - to those of their dinosaur relatives, Benson and Choiniere were able to determine whether the speed and diversity of bird leg evolution was exceptional compared to leg evolution in dinosaurs.
"What was totally surprising is that the evolution of flight didn't lead to a first great increase in bird diversity but that the loss of the long bony dinosaur tail did," says Choiniere. "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."
