The world's first birds all had four wings -- not two -- and flew with a similar construction to the Wright Brothers' Kitty Hawk plane, contends new research led by the renowned dinosaur and early avian hunter Xing Xu.
Xu, a paleontologist at the Chinese Academy of Sciences, and his team suggest this perhaps might be the simplest form of flight, as even the Wright brothers' first experiments with flight were done with a biplane in 1903.
As for how this system in birds evolved, Xu told Discovery News, "The first birds descended from four-winged dinosaurs, which are not necessarily gliders in the strictest sense."
One such dinosaur might have been Microraptor, a non-avian dino that had feathers on both its arms and legs. Paleontologists believe it could fly.
The researchers studied well-preserved fossils of 11 birds from at least four diverse groups dating from about 150 to 100 million years ago. All of the birds were found in the Jehol formation in Liaoning, northeastern China.
The ancient birds were found to have clumps of stiff leg feathers that resemble wings. Xu and his colleagues believe these were, in fact, wings, according to the study, published in the journal Science. He said they "either provided lift, or created drag, or enhanced maneuverability or a combination of all of these functions."
Xu explained that the earliest birds were primarily arboreal, so they would have flown from trees instead of taking off from the ground or water, as today's birds often do, depending on the species.
This could help to explain why birds lost the extra "wing" leg feathers over time, evolving the two-winged anatomy of today.
Xu said that this loss happened "primarily because of the evolution of two different locomotion systems in birds -- arm wings for flight and legs for walking and running."
He added that the shift from a tree habitat to ground and water ones would have also favored the loss of the leg feathers.
Sankar Chatterjee, a paleontologist at Texas Tech University, told Michael Balter of Science that the new study makes it clear that "the four-wing form was exhibited not just by Microraptor, but also retained
in successive lineages of early birds."
Kevin Padian, a paleontologist at the University of California at Berkeley, also agrees that the research establishes that leg feathers were widely distributed, but he remains skeptical that the leg feathers were, in fact, used for flight.
"No one thinks that these animals flapped their legs, so what is the argument about improving flight?" he asked, adding that "no one has performed any kind of adequate functional or aerodynamic test."
Future biomechanical studies might be on the horizon. For now, though, Xu and his team are analyzing thousands of specimens at the Shandong Museum. They believe that evidence from more fossils could help to answer some of the still-existing questions about avian evolution.