The primitive bird Archaeopteryx could have used forward thrust from its wings to reach takeoff speed.

Dinosaurs Take a Flying Leap

Today's birds make it look easy, but getting off the ground and staying in the air is no simple task. How and why the first birds managed to fly has long puzzled biologists. Now, scientists have calculated how flight could have evolved as a survival technique--to catch dinner or avoid becoming dinner. In tomorrow's Nature, they show that by flapping its feathered wings, an early birdlike creature called Archaeopteryx would have run swiftly enough to take off.

For more than a century, scientists have argued over two theories of how early birds learned to fly--by jumping out of trees, or by taking off after a running start. While many paleontologists think that birds evolved from ground-dwelling dinosaurs, initial calculations left them perplexed: The top running speed of Archaeopteryx, for example, seemed to max out around 2 meters per second, well short of the minimum takeoff speed--at least 6 meters per second.

Now, however, aerodynamicist Phillip Burgers of the San Diego Natural History Museum and paleontologist Luis Chiappe of the Natural History Museum of Los Angeles County say the early calculations left out a critical factor. By flapping its wings, Archaeopteryx could have provided extra thrust, enough to easily propel the animal beyond the speed barrier.

Flight evolved out of the need to run down prey or outrun predators, says Chiappe. But ornithologist Alan Feduccia of the University of North Carolina, Chapel Hill, says Archaeopteryx's claws look more like those of tree dwellers, with an opposing toe to grasp tree branches, than roadrunner-like animals. Anatomist and paleontologist Lawrence Witmer of the Ohio University College of Osteopathic Medicine in Athens, however, welcomes the new analysis. Scientists "have been so focused on lift--how do you get an animal off the ground and keep it off the ground," he says, "that we've overlooked the propulsion from wings. This is something new for us to chew on."