A new study has provided further evidence for the theory that birds did not descend from ground-dwelling theropod dinosaurs, and it actually might be the other way around.
In the study, scientists examined a remarkable fossil specimen of "microraptor" that had feathers on all four limbs, somewhat resembling a bi-plane.
Glide tests based on its structure concluded it would not have been practical for it to have flown from the ground up, but it could have glided from the trees down, somewhat like a modern-day flying squirrel.
Many researchers have long believed that gliders such as this were the ancestors of modern birds.
"This model was not consistent with successful flight from the ground up, and that makes it pretty difficult to make a case for a ground-dwelling theropod dinosaur to have developed wings and flown away," said John Ruben, a professor of zoology at Oregon State University.
"The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, but that some species now believed to be dinosaurs may have descended from birds," said Ruben.
"It would have been quite possible for birds to have evolved and then, at some point, have various species lose their flight capabilities and become ground-dwelling, flightless animals - the raptors. This may be hugely upsetting to a lot of people, but it makes perfect sense," he added," he added.
"We're finally breaking out of the conventional wisdom of the last 20 years, which insisted that birds evolved from dinosaurs and that the debate is all over and done with," he said.
According to Ruben, birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path, and after millions of years of separate evolution, birds also gave rise to the raptors.
"Small animals such as velociraptor that have generally been thought to be dinosaurs are more likely flightless birds," he said.
"Raptors look quite a bit like dinosaurs but they have much more in common with birds than they do with other theropod dinosaurs such as Tyrannosaurus," Ruben said.
"We think the evidence is finally showing that these animals which are usually considered dinosaurs were actually descended from birds, not the other way around," he added.