Introduction to Pterodactyls
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.
Exceptional Aerialist
Is this what life must have been like for a pterodactyl? Yes, according to new research into the anatomy and behavior of these extinct flying beasts. Fossils of pterodactyls were first dug up at the end of the 1700's, but the interpretation of their way of life suffered because scientists didn't recognize the creature's remarkable mixture of birdlike and batlike features. Now, in the mid-1990's, we have a much better picture of pterodactyls as living animals. Fossil hunters have discovered pterodactyl trackways at a dozen locations in the Western United States, and anatomists have scrutinized perfectly preserved skeletons that show every joint in the wing, neck, and body. The scientific evidence shows that pterodactyls must have been exceptional aerialists with powers of flight that were superior in some aspects to those of modern birds.
Pterodactyls (pronounced tehr uh DAK tuhls) lived during the Mesozoic Era, which began 240 million years ago and encompassed the Triassic, Jurassic, and Cretaceous Periods. They belonged to an extinct group of flying animals known as pterosaurs, fossils of which have been found on every continent except Antarctica. There were two major kinds of pterosaurs-rhamphorhynchoids and pterodactyls. Rhamphorhynchoids developed first, but were later dwarfed in size and variety by the pterodactyls. The largest flying animal ever known was a pterodactyl, Quetzalcoatlus (named after the Aztec god, Quetzal-coatl), with a wingspan of nearly 12 meters (40 feet). Some species of pterodactyls, however, were as small as sparrows.
Almost 100 different species of pterosaurs have been identified, but scientists think there must have been many more. Most pterosaur remains were preserved in coastal sands that later turned to rock, yielding the fossil skeletons found in our day. For this reason, our knowledge of these magnificent creatures is mainly limited to pterodactyls that lived near the sea, even though some species would have made their home inland.
The Early View of Pterodactyls—flying Fiends
The pterodactyl as we know it today was an extraordinary beast, elegant in design. But for most of the last two centuries, pterodactyls have been portrayed as ugly, evil, and repulsive. The first pterodactyl remains were found in a limestone quarry in Bavaria, Germany, in the late 1700's. In 1809, French anatomist Georges Cuvier bestowed the name Pterodactylus (meaning wing finger) on the fossil and decided the creature's closest living relatives would be reptiles.
Almost since that day, illustrators began depicting pterodactyls as flying fiends-part bat, part bird, part crocodile-covered with dark leathery skin. The flying-devil image of pterodactyls became standard in popular writing as well as in science texts. In the 1912 novel The Lost World, the English author Sir Arthur Conan Doyle imagined explorers stumbling upon a Brazilian plateau where Mesozoic creatures survived to the 1900's. Doyle's pterodactyls are hideous aerial scavengers that drip noxious drool as they swoop down to bite at the human interlopers. A giant pterodactyl in the 1933 motion picture King Kong was fashioned after the same image. It had black, reptilian wings, and its role in the script was to try to steal the female star, Fay Wray, by grabbing at her with its monstrous hind claws.
In the 1960's and 1970's, most museum displays and textbooks still presented pterodactyls as nightmarish beasts with batlike skin. Not only were they unappealing to look at, but these pterodactyls also were reconstructed as sloppy fliers. Pterodactyl wings were thought to be merely limp expanses of skin, making the cumbersome beasts incapable of efficient soaring flight or powerful flapping.
Snowy-white, Furry Pterodactyls
Finally, in the late 1970's and 1980's, perceptions of pterodactyls began to change. In the mind of fossil experts, pterodactyl hide was transformed from dark and leathery to snowy-white and furry. Part of this revolution in thinking came from rediscoveries of scientific work from the 1920's. At that time, German paleontologists found pterodactyl remains in Jurassic rocks that seemed to preserve an image of the fine structure of its skin. Using a microscope, scientists could see tiny hair-shaped structures that covered the body like fine fur. Few paleontologists believed the notion that pterodactyls had fur until 1970, when Russian experts announced their discovery of fossil specimens that indisputably showed the entire body covered with hair.
Once we accept the idea of pterodactyls as furry fliers, the next question to ask is, "What color was the fur?" We can find no clues from fossil bones or even fossil skin, but we can make a good guess based on nature's hard and fast rules of color. The rules are that an animal's coloration must do two things-provide camouflage in the native environment and help attract mates.
Under those rules, the 200-year-old tradition of showing pterodactyls with dark, batlike skin made no ecological sense. Nearly all of our pterodactyl specimens have been dug up from sediments formed in shallow oceans, and pterodactyl teeth and muzzles appear adapted to catching fish and squid. In other words, those pterodactyls were the Mesozoic equivalent of today's oceanic birds, like gulls, terns, and albatrosses. And what color are most sea birds? White-the best camouflage for birds that swoop down on fish swimming near the surface. A snowy underside makes the bird's body invisible against the bright sky. Therefore, most pterodactyls are likely to have had white fur on their bellies, throats, and thighs.
Pterodactyl Courtship—dabs of Color
According to the rules of ecology and animal behavior, pterodactyls may also have displayed splashes of bright color. Animals with large eyes and great powers of visual discrimination use color to communicate with each other. For example, today's bird species see a wider range of colors than humans do, and most birds use some sort of bright color patterns in the courtship season to attract mates. Dabs of red ornament the beaks of gulls, and circles of lively colors highlight the eyes of male puffins during the breeding season.
Like birds, pterodactyls must have had good vision. As long ago as the 1880's, pterodactyl skulls were found with the brain shape preserved as an impression in the sediment filling the braincase. The fossils showed that the pterodactyl brain was nothing like a reptile's brain. Instead, it possessed two birdlike features. One was the presence of huge frontal lobes, the halves of the forebrain where higher intellectual functions are carried out. The other feature was the existence of very large optic lobes (vision centers in certain animal brains), proof of exceptional vision. Pterodactyl brain impressions found in the 1980's confirmed the bird-style brain organization. So it would be logical to conclude that, like modern birds, pterodactyls used color for courtship.
Elaborate Head Crests
We can also guess where the bright colors would be on a pterodactyl body. Many Cretaceous Period pterodactyls evolved huge crests that stuck out behind their foreheads. These cranial devices would not have been useful as aerial rudders or stabilizers, and female pterodactyls seem to have had smaller crests than males of the same species. The crests make ecological sense only if they were courtship billboards—features that would beckon potential mates and frighten away sexual rivals. Many modern birds sport brightly colored crests on their heads. Hornbills, toucans, and touracos are good examples. And so it is very reasonable to suppose that males of the great Cretaceous pterodactyl Pteranodon ("toothless flier"), for example, sported a vivid crimson crest in the breeding season.
Modern bird societies are knit together by elaborate ceremonies in which males and females "exchange vows" by performing long dance routines, with much head-bobbing, prancing, bowing, and strutting. The bird-style intelligence of pterodactyls implies that their social life was complex too, and that pterodactyl courtship may have been full of instinctual choreography.
Strong Wings and Precise Flight Control
As scientists in the late 1970's and 1980's reappraised the appearance and social behavior of pterodactyls, pterodactyl flight also was reevaluated. Specimens dug up in the 1920's were examined once more, and the myth of the pterodactyl's weak, limp wings was dispelled. Fossil impressions of the wing membrane show clearly that the wing was strengthened by a network of strong, flexible fibers held together in a sheet of elastic tissue. In life, pterodactyl wings must have been tough and nearly unbreakable.
Our view of pterodactyls' abilities as a flier changed after humanity gained sufficient understanding of flight to build airplanes. We now understand that any flying machine-bird, bat, or airplane-depends upon a force called lift. For a body to become airborne and to stay in the air, there must be a lifting force on the wings that offsets the downward pull of gravity.
That lifting force is created when a wing is curved on the top and straight on the bottom. When such a wing slices through the air, the air that has to travel over the curve is forced to move faster than the air below the wing. The difference in air speed creates an area of low air pressure above the wing. Air under the wing tries to move into the low-pressure area, but the wing is in the way, so the air pushes up on the wing—creating lift. The larger the wing surface and the faster it slices through the air, the greater the lift.
Birds can soar and glide because their wings have a curve on the leading (front) edge. Airplane wings follow this design. But when airspeed is low and the wing is turned up to climb or down to land, the airflow over the leading edge may become so turbulent that air pressure no longer holds up the wing. If that happens, the flying machine will begin to drop. To combat the problem, modern aircraft have flaps on the leading edge that can be extended forward to expand the wing area and increase lift as needed.
Similarities of Pterodactyl Wings to Airplane Wings
Amazingly, pterodactyl remains show the same feature. In addition to a large wing surface and a curved leading edge, the pterodactyls had a special spike of bone on the wrist, mounted on a swivel joint. Wing-impression fossils show that this swivel bone held a leading edge flap of wing skin that could be flexed up and down into a wide range of configurations.
In airplanes, leading edge slots are another antistall device. These are holes cut into the leading edge flaps to allow air to flow smoothly over the wing at the lowest speeds. In pterodactyl wings, the leading edge flap may also have had a hole in the center, making it function as a leading edge slot.
Of Bats and Birds
Modern analysis of pterodactyl legs and torsos led to the conclusion that these Mesozoic aerialists may have been even more efficient fliers than modern birds. Flying birds operate under one major, built-in handicap: flight feathers are attached only to the front limb. Because the wing is supported only by the arms, the torso and hind legs are dead weight when the animal is flying. When in the air, a bird's body, thigh, and calf muscles cannot contribute to flight power. In fact, the bird hind leg is built to a totally different mechanical blueprint than is the arm. The leg is used for walking, jumping, scratching, digging, and climbing, but never for flying.
Bats, on the other hand, are more efficient fliers. Bat hind legs—and in some species, the tail—are attached to the trailing (rear) edge of the wing. When a bat flaps its wings, the hind leg moves up and down with the arm. That means that all the muscle power of the rear end of the body can be added to the arm power. The result is a superstrong wing stroke.
Which modern-day fliers—birds or bats—are closer in wing-leg design to pterodactyls? In the 1970's and 1980's, many experts believed that pterodactyl wings were powered only by the arms, without any contribution from the hind legs. Recreations of the animals showed them running around on the ground like birds, supporting their body weight on their hind legs.
New Evidence of Bat-style Locomotion In Pterodactyls
The discovery of fossil footprints in Colorado, Utah, and Wyoming in the early 1990's may debunk this "bird hind-leg" theory. Bird-style footprints are distinctive because only the hind feet are used for walking, and the legs are close together under the body. They do not sprawl out sideways. Bird tracks are similar to those left by meat-eating dinosaurs—such as Allosaurus or Tyrannosaurus—with the right and left hind paws hitting the ground very close to the center line of the tracks. Bats, however, leave tracks from the forefeet as well as the hind feet, and the hind feet are splayed far out to the sides. Sprawled-out hind feet are necessary to hold out the trailing edge of the wing when the bat flies.
The newly discovered pterodactyl tracks show pterodactyls walking like giant vampire bats, with the arms and legs spread sideways. The wide spread of the hind legs is evidence that pterodactyl hind legs were attached to the wing. These tracks indicate that pterodactyls did not walk like birds.
More evidence for a bat-style locomotion comes from the tail bones of one of the largest pterodactyls, Pteranodon. The bones include special tail rods that probably attached to a rear wing extension running from tail tip to hind leg. And wing imprints from other pterodactyl species show that the trailing edge of the main wing was firmly anchored to the thigh and calf.
Maximizing Power For Flight
With this anatomy, a pterodactyl could put nearly 100 percent of its total body muscles to work when flapping its wings, the hind leg muscles working in concert with the arm muscles. Typical backboned animals have a considerable mass of muscle that helps move the backbone in the torso. In birds and bats, these trunk muscles are useless for flight. Advanced pterodactyls such as Pteranodon had less weighty muscles running along the backbone. Instead they had a special plate of lightweight bone that strengthened the torso and the shoulders. In this way, most of the muscle groups that could not contribute to flying were eliminated.
Any giant flying animal faces its greatest challenge when trying to take off. Large pterodactyls met the challenge with several anatomical features. First, they had many square feet of wing per pound of body weight, which meant that a single wing flap could provide plenty of upward force. Second, their sharp wing claws enabled them to climb up trees or along cliffs, so they could gain some height for the take-off. Third, a special feature of the shoulder allowed pterodactyls to gain extra downward thrust from their wings during the crucial first leap into the airstream.
That feature makes pterodactyl shoulders marvels of aeronautical engineering. Advanced species had an extra pivot joint between the upper end of the shoulder blade and the bone plate that stiffened the torso. No other backboned animal has this joint, which lets the shoulder swivel. The very long shoulder bone could swing up and back as well as down and forward, movements that would increase the power of the wing downstroke.
The Great Fish Hunter
No matter how good the flier, hunting fish from the air isn't easy. One big problem is that when an aerial fisher swoops down and jabs its beak into the water, it can reach only those fish that are swimming close to the surface. A very few modern sea birds escape this limitation by using the plunge-diving technique. We can see the technique in the brown pelicans that fish off the California coast. These big birds circle slowly in the air until they spot their fish target. Then they dive straight down. Just before they hit the surface, they fold their wings against their sides, giving their bodies the shape of an armor-piercing bomb. The pelican penetrates the water to a depth of several feet. Then it opens its huge mouth and sucks in prey.
Giant Cretaceous pterodactyls of the Pteranodon family were also built to be plunge-dive bombers. The Pteranodon head was huge and pelican-shaped, with a long, pointed bill. But penetrating the water at high speed is dangerous—the force could twist the head right off the neck. To strengthen the neck against the shock of hitting the water, Pteranodon had extra joints on the underside of each neck bone that locked each bone in place. During the dive, the pointed bill, head, and neck became as rigid and deadly as a spear.
Pteranodon also had expandable lower jaws like those of today's pelicans. When the great pterodactyl plunged deep into the water, it could open its throat pouch wide and suck in fish or squid. Altogether, these pterodactyls had a plunge-diving design that was unequaled in efficiency until the pelicans themselves evolved 60 million years later.
If pterodactyl images have come a long way since King Kong, it's because pterodactyl science has come a long way. The creatures no longer have the reputation of being nasty and devilish. Indeed, as scientists fine-tune their knowledge of pterodactyl anatomy, the pterodactyl is becoming one of the most admired of Mesozoic species.