The dinosaur had two sets of feathered wings, on its forelimbs and hind legs and is believed to have “flown” like a flying squirrel – gliding, but incapable of true flight.
The Chinese scientists who found the Microraptor fossil proposed that when it glided between trees, it spread out its legs and kept its wings one behind the other in a tandem pattern similar to a dragonfly.
“We knew that there was something wrong anatomically. There is just one choice. It has to have this biplane wing design”
But using computer models and anatomical analysis, Sankar Chatterjee, a paleontologist at Texas Tech University, and Jack Templin, an aeronautical engineer, decided that such an arrangement could not have worked.
Chatterjee proposed that Microraptor positioned its hind legs below its body, adopting a “biplane” arrangement.
He said: “We knew that there was something wrong anatomically. There is just one choice. It has to have this biplane wing design.”
A computer flight simulation of Microraptor employing this wing arrangement demonstrated it would undulate up and down, necessary for gliding among trees, and may have been able to glide over a distance of 40 metres.
It is widely believed among paleontologists that the first birds arose from small, feathered dinosaurs.
“From trees down”
Microraptor lived roughly 30 million years before the earliest-known bird, but Chatterjee said it may represent a throwback form that was an intermediate stage in bird evolution.
The researchers also acknowledge this biplane design may have been a failed evolutionary experiment that did not lead to birds.
Chatterjee said: “Basically what happened is there is a transition from biplane to monoplane.
“If you look at Archaeopteryx and all other birds, they have this typical monoplane design.”
Pedopenna, another small dinosaur known only from partial remains, may also have used a biplane gliding arrangement, he said.
Other theories suggest birds evolved from little dinosaurs that were running and jumping from the ground, or that birds evolved from small dinosaurs living in trees that initially used feathers to control their descent like a parachute, before evolving a method of flight.
Chatterjee said the reassessment of Microraptor “settles once and for all that flight really evolved from trees down”.