Introduction

Flight by animals extends back in time to the very beginning of vertibrates (animals with a backbone) some 200 million years ago. Since these animals no longer exist scientists do not always agree about how good they were at flying, where they came from or what happened to them. Were flying lizards (dinosaurs) warm blooded or cold blooded? Were they fast or slow? Did they fly or only glide? In this section we will follow one line of thought and point out controversial areas (where scientists do not agree with each other).

Today it is generally believed that some species of dinosaurs did fly as much and as well as modern birds and bats. These flying dinosaurs, known as pterosaurs (flying lizard) lived all through the same time period as the non-flying dinosaurs. Dinosaurs are believed to have lived from approximately 230 million to 65 million years ago. Towards the end of this time the Archaeopteryx appeared. It is believed to be an early bird. It had feathers and the same general features of most birds today.

Pterosaur - "Winged Lizard" and Pterodactyls - "Winged Finger"

The Pterosaurs lived in a variety of shapes and sizes which allowed them to exist in several different environments. One of the best known Pterosaurs is the Pterodactyl or "wing-finger". Artists have drawn pictures of the Pterodactyls showing them as a very large flying creature with sharp teeth in its beak and a long, dangerous looking tail. The older fossils go along with this image, but fossils from a later period show that Pterodactyls were not much bigger than a modern pidgeon and probably used its long snout (nose) to probe for worms in holes along the beach!

It is true that some of the Pterosaurs were very large, one with a wing span of 51 feet! But, many of the Pterosaurs were much smaller, even as small as a sparrow. The most common were the size of a chicken or raven. Fossils of Pterosaurs have been discovered mostly in areas where there was much water. It is believed that the Pterosaurs would sit on the water, like a gull, and catch marine life for food. Some even had strainer like teeth which could be used as a sieve for food from water in swamps and marshes, much like flamingos do. It is believed that Pterosaurs spent most of their time on the water, but had the capability of walking on land, usually to nest.

One of the strangest Pterosaurs was the Rhamphorrhynchus. It also had a tapered, pointed snout, sharp needle like teeth, but, these teeth were facing forward and slightly outward from the mouth. This was very unusual. It is thought that this Pterosaur used its beak to spear fish while flying low over the water!

The Dimorphodon was a Pterosaur which had a stout but massive jaw with sharp opposing teeth. With its "S" shaped neck, which could staighten and snap foward, it could catch its prey quickly.

Another strange adaptation was the Pteranodon which had a crest or protrusion on the top of its head sticking out as far as its jaw was long. Its skull was in the middle with its long toothless snout facing forward and is long crest on its head facing rearward. The function of this crest is unknown.

The Long and Short of It

Although the fossil record is not complete, it shows a wide variety of Pterosaurs that seemed to fit into many environments, just as today's birds. Just as the Pterodactyls changed from one period to another so did many other Pterosaurs. The early Pterosaurs and the later Pterosaurs differed from each other in some significant ways. From the fossil record it seems that all of the early ones tended to be larger and have a long tail, whereas the later Pterosaurs were smaller, had relatively short, stout bodies and a short tail.

Some of the long tail Pterosaurs had a kite like structure at the end of their long tail that is believed to have been used like a rudder to help balance the creature in flight. There were long tail Pterosaurs without the kite structure. These larger Pterosaurs had narrow wings compared to the later, smaller short tail Pterosaurs. The short-tails had wings which allowed greater maneuverability in the air (ability to make turns). But, even some of the later "smaller" short-tail Pterosaurs were large. The Pteranodon with a wing span of 21 feet and Quetzalcoatlus with a wing span of up to 36 feet!

Gliders or Flyers?

In comparing a bird, bat or Pterosaur to a gliding animal such as a flying squirrel one can see some very important differences. The Pterosaur, bird and bat all have distinct wings in the way we are used to seeing. These wings have a distinctive shape which can allow for true flight and a bone structure which supports the wing. Whereas, other "flying" mammals such as the flying squirrel have a loose flap of skin that stretches between its front and hind legs. The birds and bats can control and alter the shape of the wings to increase lift, adjust to the speed of flight, alter direction (turn), climb and dive at will. flying squirrels, however, can basically glide downwards with few turns possible, compared to birds and bats. Birds and bats have powered flight which not only allows them to maneuvere (change speed and direction) but to sustain (continue) flight for long distances or time. While flying squirrels can use flight to escape danger, birds and bats use flight for this and much more, such as hunting and other food gathering, finding mates, and seasonal migrations to name a few. Their entire lives are built around flight since their bodies are totally adapted to flight.

Since Pterosaurs have been found in many different environments, like birds, they too must have been completely adapted to flight. The flying squirrels live in and around trees and don't use their flight except when necessary. They don't use flight to hunt, migrate, or find a mate; only when they need to go from one tree to another. The ability to glide, however, does not mean that one lacks the ability to fly. The albatross, for example, is one of the most accomplished gliders in existence, but it is fully capable of powered flight as are other birds. Birds such as the albatross have worked gliding into their normal flight regimen in order to save energy and to be able to stay up in the air for longer periods of time. More than likely the Pterosaurs which lived in the coastal regions had similarly adapted gliding into their normal powered flight for similar reasons. It seems that powered flight and gliding go hand in hand for birds and Pterosaurs.

A close comparison can be made between the Pteranodon and the modern frigate bird based on their shape, size, height and low wing loading.

The modern frigate bird dwells on cliffs and rears its young there. But due to its size and aerodynamics it is in every respect a soaring bird. If it lands on the water or on land (away from a cliff) it will have a very difficult time getting airborne again. It obtains food at sea by flying low and slow near the water and scooping up its prey. The frigate bird can stay aloft for many hours over water. It can do this by soaring (little movement of wings) for the majority of its time at sea.

Although there is no evidence to support the conclusion that the Pteranodon lived a similar life style, it is not difficult to imagine a pterosaur with similar traits living and roosting on cliff tops, jumping to get airborne, and spending the day soaring. When it spots prey, like a fish, it swoops low and slow until it catches the fish with its jaws, while airborne. The similar shapes and similar life styles, of the frigate bird and Pteranodon make this a distinct possibility.

The Shape of the Wing

The shape of the wing of Pterosaurs is very similar to that of both bats and birds. It, in some ways, has features of both. Although there are some obvious differences between bat and bird wings, there are also many similarities. Both the bat's wings and bird's wings provide lift and are very efficient for powered flight. Perhaps the bat wings are better adapted for slow flight and birds for faster flight.

In addition to the fossils found of Pterosaurs, impressions(marks in the mud) of their wings and bodies have also been found, probably where the creature died in the mud. The immpressions show that the Pterosaurs had membrane type wings similar to bats, but longer and narrower like modern birds. The impressions also showed muscles in the wings which would indicate the wing membrane was taut (tight). This leads us to believe that Pterosaurs had precise flight control as in modern birds and bats and that they were accomplished flyers. The implication is that the wings of Pterosaurs allowed the same type flying as modern flyers. Modern birds are slope soarers and thermal soarers. Thermal soarers are those birds which glide and maneuver in rising thermals like eagles. Whereas, slope soarers are those which glide in winds whcih form on an up slope or along waves; seagulls and albatross are examples of this. It seems likely that Pterosaurs probably had adapted to both thermal and slope soaring since the build and shape of their wings are very similar to modern birds and bats.

Body Structure

Typically the Pterosaurs had a short and stout body structure relative to its overall size. Like modern birds, its chest and back area near the wings had bone structure and breast bone which allowed for secure anchorage of its powerful flight muscles. The short body structure kept the center of mass near the center of lift and allowed for proper balance during flight.

The head was very long when you include the snout and crest, longer than the body! Its neck was long and seems to have been quite maneuverable allowing the head to be moved as needed to snag (catch) prey.

Pterosaurs had a wing structure made up of bones from its little finger. The other fingers extended outward making a claw. It is thought that the Pterosaur was able to get around on the ground quite well with its wings folded and walking on its hind legs and three finger claw on its front arms (wings).

The Pterosaur bones are amazingly light in weight. Most of the bones found were hollow with a light reinforcing structure in critical (important) stress areas. It is believed that these bones were hollow and not filled with marrow, but with air sacs like modern birds. Comparing the same size Pterosaur with a modern bird, the Pterosaur was much lighter in weight.

Further examining of the fossil remains (bones) found possible attachments for powerful muscles. A Pterosaur would need these muscles to sustain powered flight, even soaring flight. The smaller Pterosaurs were probably not soarers but rather conventional flyers such as smaller birds, sparrows and pigeons that all require involved muscle systems. It seems likely that the muscle structure of Pterosaurs was just as complex as modern birds and bats.

There are other features that Pterosaurs were likely to have in order to be successful as flyers. We don't know if Pterosaurs were warm blooded or cold blooded. Birds and bats are warm blooded and live in almost every climate or environment. Warm blooded animals can regulate (control) their body heat by either exercising muscles to warm up or shedding heat to cool off. For sustained muscle power and powered flight a creature defined as warm blooded seems to be a necessity. This makes them very efficient (able to adjust to different climates) and would be very useful to flyers in different environments. Pterosaurs lived in almost every environment. There are no modern cold blooded fliers. From this we may speculate (guess) that Pterosaurs were warm blooded.

Assuming that the Pterosaurs were warm blooded then comes the question of insulation (body cover) to allow control of heat loss. Evidence in the fossil finds of Pterosaurs indicates that the bodies may indeed have had a fur or feather like covering which was probably not quite feathers as we know them or fur as we know it, but was similar and protected the body from heat loss. This covering appears to be a kind of scale like feathers, but not quite like feathers. However, there is no evidence that the wings had any covering. All the evidence shows the wings as being membrane type structures. Therefore, it appears that the wings were bare membrane and the body was covered in a feather/scale type structure. This is very similar to what is found on bats today. This is another indication that the Pterosaurs developed in a similar way to the modern birds and bats.

Another issue is speed of flight. Once again ther is no direct evidence. The Pterosaurs developed different classes to fit different environmental niches (places) the same as bats and birds of today. Birds have developed wings which cover all ends of the spectrum from the very slow to the very fast and everything in betwen. The largest flying birds are relatively slow, but can soar for long periods of time whereas birds such as the swift can hit speeds in excess of 100 mph. The hummingbird, on the other hand can hover in order to get at nectar in flowers. Bats behave in a similar way. The fossil evidence indicates that some Pterosaurs were soarers and hence relatively slow while others were probably relatively fast. Since Pterosaurs had seemingly frail skeletons that most likely limited their airspeed to speeds which were appropriate for the strength of their body structure. Pterosaurs too seem to have covered the entire speed range of flight.

The evidence is good that Pterosaurs filled all the niches of the environment and were indeed highly successful fliers who survived for 157 million years which is no small feat (success).

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Last modified: Mon Jun 1 13:34:16 PDT 1998

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