A new study worked to pinpoint when avian ancestors developed their wings.
Birds are believed to have developed from 150-million-year-old theropod dinosaurs called maniraptorans. The creatures had bird-like features such as high metabolic rates, small bodies, hollow bones, and even feathers, a Mcgill University press release reported.
"This work, coupled with our previous findings that the ancestors of birds were not tree dwellers, does much to illuminate the ecology of bird antecedents." former grad student Alexander Dececchi, now a postdoctoral researcher at the University of South Dakota, said. "Knowing where birds came from, and how they got to where they are now, is crucial for understanding how the modern world came to look the way it is."
Researchers studied fossil data to determine when and how the change from arm to wing took place. They found that body-to-limb length ratios remained fairly standard throughout most of fossil history, until the "birds" exhibited a "dramatic decoupling" from the body size in the forelimbs and hind limbs.
The forelimbs eventually got long enough to work as an "airfoil," which opened the door for the development of powered flight. Eventually the hind legs shrank, allowing for better flight control in the earliest birds. Today's birds tuck their legs underneath them during flight to further reduce drag.
"Our findings suggest that birds underwent an abrupt change in their developmental mechanisms, such that their forelimbs and hind limbs became subject to different length controls," Hans Larsson, Canada Research Chair in Macroevolution at McGill's Redpath Museum, said. "This decoupling may be fundamental to the success of birds, the most diverse class of land vertebrates on Earth today."
At the same time as the birds were perfecting flight, a ferocious dinosaur called the pterosaurs dominated the sky and competed for vital food sources. The efficient development of flight would have been crucial to the bird's survival.
"The origin of birds and powered flight is a classic major evolutionary transition,"Dececchi said. "Our findings suggest that the limb lengths of birds had to be dissociated from general body size before they could radiate so successfully. It may be that this fact is what allowed them to become more than just another lineage of maniraptorans and led them to expand to the wide range of limb shapes and sizes present in today's birds."
