"The feather arrangement in Archaeopteryx and Anchiornis wouldn't let them do this," he added, "so it may have made takeoff from the ground and flapping at low speeds more difficult."
Gliding, however, must have been a lifesaver back in the dinosaur day, when huge terrestrial carnivores were stomping around.
"Gliding is a fast way to move from tree-to-tree. Instead of climbing down one tree and running up the next, you just glide quickly from one to the other," Longrich explained.
"I would imagine that the dinosaurian ancestors of birds were living in the trees," he noted, "probably to find food-like insects, lizards and mammals, and to avoid becoming food for other dinosaurs."
Longrich and his colleagues believe that the wing feather arrangement seen in modern birds may have evolved within a period spanning a few tens of millions of years and then remained largely unchanged for the past 130 million years.
In terms of this short versus long timescale, Longrich compared it to the evolution of human-constructed aircraft, which started with some years of experimentation before settling into a basic design that's just been fine-tuned during more recent years.