For years scientists have argued about how dinosaurs became birds and learned to fly. Did they run along the ground real fast, flapping their wings until they took off? Or did they climb into trees, spread their wings and glide?

The answer, it turns out, may be: Both.

Two discoveries reported this month show that feathered dinosaurs who lived on the ground may have used small wings to help them run up the sides of trees. And once they got up there, they started to glide.

In Montana, biologist Kenneth Dial showed how chickens, turkeys and other big-legged birds who are not very good fliers use their wings to press their bodies against any surface. This gives them better traction so they can run up steeper slopes. Dial made a slow-motion video showing that a partridge -- a bird a lot like a turkey -- was even able to run straight up a post.

Then, a week later, Chinese scientist Xing Xu reported discovering the fossil of a feathered, pigeon-sized dinosaur 130 million years old. It had four wings -- one on each of its front and back legs. Xu said the back feathers made it difficult for the dinosaur to run. But they would be ideal for gliding -- sort of like a flying squirrel.

Both of these ideas are new. Nobody knew birds ran up trees, because they do it so fast you can hardly tell what's happening. Dial was interested in how baby partridges jump, but it was his 13-year-old son, Terry, who noticed they were "cheating." However they were getting up that post, they weren't jumping.

And nobody had ever seen a dinosaur with four wings. So when it comes to figuring out what it all means, "we've got a lot of work to do," Ohio University biologist Lawrence Witmer admitted.

Still, it looks like these two discoveries may help solve an important scientific riddle. Most scientists have believed for a long time that birds evolved from dinosaurs. They just didn't know how it happened.

The problem was legs. Working in China, scientists such as Xu have found fossils of several small, feathered, meat-eating dinosaurs. These animals, known as raptors, are thought to be the ancestors of modern birds. The pterosaurs -- pteranodons and pterodactyls -- are flying reptiles that became extinct.

The trouble with raptors is that they were all runners with big hind legs, and big hind legs are no good for flying. Just look at the tiny legs of almost any small flying bird.

Fortunately, though, Dial noticed that a bunch of modern birds have the same problem, beginning with the common chicken. These "ground birds" can fly, but not very well. This is because their strength is in their hind legs.

And this is why "dark meat" is dark. There are more blood vessels in the hind legs. More blood means more energy. Chickens use their hind legs (drumsticks and thighs) all day long, but their wings can only give short bursts of strength -- enough to push them, it turns out, while they run up steep slopes. You'd be able to walk up a wall if somebody was pushing you toward it.

So once raptors got into the trees, what happened? Well, the Chinese fossil suggests that they grew feathers on the hind legs and glided from branch to branch. Still, those are pretty big legs to be dragging around. If true flying is what you're after, you want to have legs like a sparrow, not a turkey.

So what happened next?

Well, as Witmer said, there's still a lot of work to do.

-- Guy Gugliotta

Chinese scientists say a four-winged dinosaur, Microraptor gui, may have glided from tree to tree.Montana biologist Kenneth Dial thinks that dinosaurs, like partridges, may have figured out a way to propel themselves up steep inclines.