Archaeopteryx had a pretty decent wingspan for a half-pound bird, more than 20 inches. That should have been ample to keep the crow-sized bird flying, or at least gliding, through the Jurassic skies. But as anyone who’s ever watched a space shot knows, the toughest part of flying is the takeoff. And the first birds and their dinosaur ancestors just didn’t have the specialized muscle power for liftoff that their modern counterparts do. It’s a question scientists have been arguing about for more than 200 years: how did the first fliers generate the lift to conquer gravity and take to the air A new study in the journal Nature shows how it could have been done.
Fly-of-die According to this popular theory a tree-dwelling ancestral bird could have launched itself or fallen from its perch and managed to stay aloft with the panicked flapping of feathered forelimbs. That solves the gravity issue, but Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County, poins out a problem. "We don’t know of any bird ancestors that lived in trees." The first paragraph points out that one of the most difficult problems for Archaeopteryx to take to the air is______.
[A] its weight [B] its muscle power
[C] the gravity issue [D] its wingspan

A running start This could have helped a bird like Archaeopteryx into the air, but its estimated top ground speed wasn’t anywhere near fast enough for liftoff. Chiappe teamed with industrial aerodynamicist Phillip Burgers, who spends his days designing fans and blowers, and just happens to have earned a Ph. D. studying avian flight. The two used aerodynamic theory and biomechanics to re-create the takeoff run of Archaeopteryx. During a run, the researchers found, the bird’s wings were able to rotate by 45 degrees at the shoulder, angled forward like two large oars beating the air. That may have provided the extra burst of speed Archaeopteryx needed to outrun hungry predator or snap up a quick-running lizard. And, the new calculations show, it would also have generated sufficient velocity for takeoff. During the early phase of a run, Burgers explains, Archaeopteryx’s wings acted more like an airplane’s engines than its wings, providing more thrust than lift. Then, once in the air, Archaeopteryx would have rotated its wings back to horizontal, to maintain altitude. Burgers holds that modern birds do exactly the same thing. Why did no one notice until now "We’re infatuated with lift," says Burgers, "because we can’t generate it ourselves. "Chiappe and Burgers have shown that Archaeopteryx could have taken off from the ground, but whether or not it actually did may never be known. "I don’t really care if Archaeopteryx flew or not," says Burgers. After all, people still ask the same question about chickens. "Does a chicken fly Maybe, maybe not. ’But its wings help it get where it needs to go. Flying, it turns out, is just the continuation of running by other means.