BEIJING, May 6 (Xinhua) -- A Chinese study found that running may have caused early winged dinosaurs to flap their wings before they evolved the ability to fly, providing new insights into the origin of avian flight.
Since a nearly-complete Archaeopteryx fossil specimen was discovered in 1861, there has been a debate on "gliding or flapping" when researchers discuss how these primitive birds once flew.
Some researchers suggested that the Archaeopteryx, which lived about 150 million years ago, probably glided between trees as shafts in their feathers could not stand up to flapping. Some researchers hold a different opinion, suggesting the wings of the Archaeopteryx could withstand active flapping.
In the new study, researchers from Tsinghua University and the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, chose the Caudipteryx as the candidate to explore how running may have played a part in the evolution of flight.
Living about 125 million years ago, the peacock-sized Caudipteryx, like the Archaeopteryx, belong to a group of dinosaurs called maniraptoran, which includes birds and some non-flying dinosaurs.
In the U.S. journal of PLOS Computational Biology, researchers reported that they first used a mathematical approach to analyze the mechanical effects of running on various parts of a Caudipteryx -- body, two legs, two wings, tail, neck and head.
Calculations revealed that with an estimated maximum running speed of 8 meters per second, running speed between about 2.5 to 5.8 meters per second would have created forced vibrations that caused the dinosaur's wings to flap.
To test the calculations, researchers built a life-size robot of the Caudipteryx that could run at different speeds, confirming that running caused a flapping motion of the wings.
They also verified the results on young ostriches that weigh 4.7 kg, similar to a middling Caudipteryx. The scientists fixed the ostriches with artificial wings which are equipped with sensors to measure the lift, thrust or drag forces produced by the wings while running.
A total of four sets of wings in different sizes were tested. The results showed that running indeed caused the wings to flap, and longer and larger wings provide a greater lift force.
"Our work shows that the motion of flapping feathered wings was developed unconsciously and naturally as the dinosaur ran on the ground," said Zhao Jingshan, a corresponding author of the study from the Department of Mechanical Engineering, Tsinghua University.
"Although this flapping motion could not lift the dinosaur into the air at that time, the motion of flapping wings may have developed earlier than gliding," he said.
In future studies, researchers plan to analyze the lift and thrust of the Caudipteryx's feathered wings during the passive flapping process.