Imagine that you're a pterodactyl, walking on a warm, sandy beach in the area that is now Wyoming, 90 million years ago in the Cretaceous Period. You feel the rippled sand press against your sharp hand claws, three on each forefoot. Your four long, straight hind claws leave a forklike mark on the beach each time you take a step. You waddle quickly as you work your way up a low sand dune, elbows and knees swinging outward through wide arcs. You look like a combination of a giant toad and a fruit bat, awkward and sprawling in your gait.

When you reach the crest of the dune, you pause. You feel the off-shore breeze blowing over your snow-white fur. The wind grows stronger. You crouch down, bending at the elbows and knees. Then you leap straight up.

In one massive, coordinated contraction, your huge chest muscles thrust your arms down, and your legs push off against the ground. As your body hurtles upward, you snap your wings open, and their immense white surfaces catch the breeze. You are airborne.

You ascend hundreds of feet in an upward spiral, scanning the shallow water below for a telltale sign of prey. You see lizardlike plesiosaurs, 6 meters (20 feet) long, using their penguin-style flippers to chase ammonites, the armor-plated ancestors of squid. Sea turtles with wide, flat bodies probe the sandy sea-bottom for clams.

But your huge, birdlike eyes are searching for something else. Suddenly you spy surface ripples caused by a school of mackerel-sized fish. You lower your left wing tip and begin a steep, banking turn. You zero in on the dark form of your target. You fold your wings against your body. You become a streamlined missile, hurtling straight down into the school of fish.

With a splash, you pierce the water, your head and neck as rigid as a strong spear. "Thwunk!" Your muzzle tip skewers a fat fish as you plunge underwater. You extend your wings to a half open position and rise triumphant to the surface.