CANBERRA: The origin of powered flight in modern birds was in biplane-like dinosaurs living in trees 125 million years ago, according to a new U.S. and Canadian study.
“The origin of avian flight has been debated for a century,” said co-author Sankar Charterjee from Texas Tech University, in Lubbock, USA. His team claim to have finally settled the long-standing debate, discovering that powered flight developed from dinosaurs that glided down from trees, rather than taking off from the ground.
The team, who reported their results today in the U.S. journal, Proceedings of the National Academy of Sciences, studied fossils of the feathered dinosaur Microraptor gui, which lived 125 million years ago in the early Cretaceous period in northeastern China. Microraptor was around 77 cm long, including its tail, and weighed about 1 kg.
When Microraptor skeletons were first discovered in 2003, scientists were surprised to find that they had not one set of wings, but two. In addition to the ‘standard’ wings on the animals’ forelimbs, Microraptor‘s feet and legs sported flight feathers as well. At the time, scientists thought two sets of wings sat behind one another in tandem, a bit like a modern-day bat.
But Charterjee, and his Canadian colleague R. Jack Templin, realised that the wings were actually positioned with one set of wings above the other, like early biplanes.
The team realised that this wing configuration could not provide a Microraptor with powered flight; the dinosaurs would have been capable only of gliding. More importantly, the dinosaur had no way of lifting their wings up, so during a ground-based take-off the wings would have been damaged.
By analysing the dinosaur’s aerodynamics, the researchers calculated that Microraptor could have travelled more than 40 metres with a small jump from a tall tree. It would have fallen quickly to begin with, but then could have swooped back up to land on the branch of another tree.
According to the researchers, “this mode of transportation would have been energetically very efficient for Microraptor.” Gliding between trees doesn’t require much energy because it is assisted by gravity, they said.
Further analysis of the feathers and wings showed that the Microraptor could not have landed on the ground after jumping from a tree. The wings were not capable of acting like a parachute, and they would have crashed into the ground at up to 8.7 metres per second – enough to cause serious injury.
According to the study, this four-winged gliding system could have occurred on the evolutionary tree in one of two places. Either it was an evolutionary experiment in one group of dinosaurs that eventually failed, or avian flight went through a four-winged stage before losing one of the sets of wings.
Fossil evidence supports the latter view, according to the researchers, because the skeletons of six other dinosaurs that lived from 140 million to 125 million years ago show a gradual shift from wings on both hind and forelimbs toward wings only on the forelimbs.