Introduction

Flight by animals extends back in time to the very beginning of vertebrates (animals with a backbone), some 200 million years ago. However, our understanding of these flyers is not very complete and is very controversial in how good these animals were as flyers, what their origins were and what became of them. As with our understanding of most dinosaurs, the various beliefs held by some scientists today are challenged by other scientists. For example, were dinosaurs warm blooded or cold blooded? Were they fast or slow? Did these flyers fly or only glide? In this section we are taking one set of views and bringing them forward. Wherever possible we are also pointing out the controversial areas.

Today it is believed that some species of dinosaurs did fly as much and as well as modern birds and bats. In addition, these flying dinosaurs, known as pterosaurs (flying lizard) spanned the whole time period of dinosaurs. Dinosaurs are believed to have existed from approximately 230 million to 65 million years ago. The various species of Pterosaurs lived during most of this time period. Towards the end another type of flying vertebrate, the Archaeopteryx, came into being. The Archaeopteryx is believed to be an early bird. It had feathers and the same general layout of most birds today, however, it had teeth instead of a beak and it had a long tail. Neither of these features exists in birds today.

Pterosaur - "Winged Lizard" And
Pterodactyls - "Wing-Finger"

Pterodactyls, meaning "winged finger", were a part of the broader classification known as Pterosaurs which means "winged lizard". Pterodactyls were referred to as a "winged finger" flyers because of the construction of the wings. Their wings were different than either birds or bats, yet seemingly effective at flight. The inner portion of the wing was formed by the arm and forearm as in birds and bats, but the outer portion was formed by one finger with the other three fingers in the middle front of the wing. Pterosaurs broadly covers all of the varieties of flying dinosaurs.

When They Existed

The Pterosaurs existed from near the beginning of the age of dinosaurs (late Triassic - 220 million years ago) to the end of the age of dinosaurs (late Cretaceous - 63 million years ago). This means that the pterosaurs lived in and dominated the skies for about 157 million years. They were in the air for more than twice as long as they have been gone!

The Many Varieties

The Pterosaurs existed in a variety of shapes and sizes which probably allowed them to fill many niches in their environment. Similar niches today in our environment are filled by birds and bats today.

The Pterosaurs ranged in size from those of small birds today to true giants. Most common were those the size of a chicken or raven. The fossil remains are found mostly in areas that were coastal shallows during the time of the dinosaurs. Other Pterosaurs, at the other end of the spectrum, were found in what were inland plains and were up to the size of a DC-3 aircraft. Specialized Pterosaurs are believed to have used their long tweezer like snouts to reach into holes in the ground or between rocks to extract their next meal. While others had strainer like teeth which could sieve for food from water in swamps and marshes, much like flamingos do today. Imagine if they would take on the color of their food as flamingos do. Pink dinosaurs, quite a sight to imagine.

The Quetzalcoatlus, the largest Pterosaur found to date, is believed to have had a wing span of up to 63 feet. The size of a modern aircraft such as a DC-3. Its actual size is debated, along with its ability to fly or glide. From the fossil record, fossilized bones, only a certain amount of information can be obtained, the rest deduced. So its likely that the Quetzalcoatlus will remain controversial for quite some time.

Another Pterosaur, the Pterodactyls, had a long but stout neck and a long fine toothed snout and most likely would use its snout to probe worm holes for worms along sandy beaches. It was not much bigger than a modern pigeon.

One of the strangest Pterosaurs was the Rhamphorrhynchus. A tapered pointed snout, sharp needle like teeth, not an unusual combination for a Pterosaur. But, these teeth were facing forward and slightly outward from the mouth. This was very unusual and unique. Speculation as to the function of this odd combination leads one to believe that the purpose was to assist in catching fish. More aptly spearing fish, probably while in low flight over the water. A strange but seemingly effective adaptation.

The Dimorphodon was a Pterosaur which had a stout but massive jaw with sharp opposing teeth. Obviously the Dimorphodon had the ability to quickly snap its jaw down on its prey. With its "S" shaped neck which could straighten and snap forward and its powerful sharp toothed jaw this Pterosaur was a formidable predator.

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 its long crest on its head facing rearward. The function of this crest is unknown.

Clearly, the Pterosaurs had adapted to a variety of environmental niches just as modern birds have. Although the fossil record is sparse and represents snap shots in time, the random view it affords us of Pterosaurs indicates that these creatures had successfully adapted to the vast varieties of conditions which existed. Undoubtedly, other undiscovered Pterosaurs existed which we don't know of that had adapted to other environmental niches. The fossil record does not indicate the incredible variety of birds as we have today. But considering that for an animal to be fossilized an animal must die under conditions which allow the bones to be undisturbed and to be preserved. A shallow lake bed, a slow running river, a swamp, buried in a sand storm and other areas which can yield a good fossil in a few million years. Most animals that die do so in areas where the carcass is fed upon and the bones scattered, or the bones are chewed up, or destroyed by the intense sun. Generally, the prevalent conditions don't permit the remains of an animal to be fossilized. The rarity of an animal being fossilized, being discovered, and becoming available to have its story told must be incredible. The richness of the current fossil record, when considering the difficulty of being fossilized, surely must indicate that the life that existed then must been vast, diverse, and abundant.

The Long and Short of It

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. The Pterodactyls with the long tails came first but disappeared after the Late Jurassic period. The Pterodactyls with short tails came later and existed until the end of the age of dinosaurs.

The earlier Pterosaurs, the long-tailed Rhamphorhynchoidea, tended to be bigger and more graceful, but it is assumed less maneuverable. Some had their tails end in a kite like structure. Their wings seemed to allow better gliding and perhaps the ability to fly and soar for longer periods. They probably appeared more graceful in the air than the short-tails would later. I'm sure that the dinosaurs below probably didn't pay much attention to their gracefulness.

The kite like tail may have acted as a rudder and helped to balance the creature in flight. Perhaps it had some other use which we don't know of. However, many other long-tail Pterodactyls of the era didn't have a kite like structure on their tails. Therefore, it can be assumed that the ones that did have the kite tail had some use for it. To date the only plausible explanation is that the kite tail acted as a rudder. The wing on the long-tails was different that the wing on the later short-tails. The short-tails had wings which allowed greater maneuverability. Perhaps the kite tail helped increase the maneuverability of the long-tail Pterodactyls.

The short tail Pterodactyls, the Pterodactyloidea, tended to have more stout bodies and seemingly broader more powerful wings. Most likely they were more maneuverable than their predecessors. Even though, by and large, the short-tailed Pterosaurs were smaller than their long tailed predecessors, the largest creatures ever to fly were short-tailed Pterosaurs. The Pteranodon with a wing span of 21 feet and the Quetzalcoatlus with a wing span of upwards of 36 feet were both short-tailed Pterosaurs.

Gliders or Flyers

Both types of Pterosaurs had something in common, they flew and seemingly flew well for a total of 157 million years. They filled every niche of which flying animals could. And they were totally adapted to flight. Modern birds can pretty well make the same claims, in fact many believe that modern birds have dinosaurs as their ancestors. Although, it is believed that they do not have Pterosaurs as their direct ancestors. Modern bats also exhibit some of the same characteristics as both birds and Pterosaurs, but are not related to either birds or pterosaurs. The question arises of whether Pterosaurs achieved and sustained powered flight or merely were gliders. If they had powered flight the apparent similarities to bats and birds makes sense in that the similar adaptations which allow birds and bats to fly did indeed do the same for Pterosaurs. However, if they only were gliders, much of this adaptation seems to have been excessive.

In comparing a bird, bat or Pterosaur to a gliding animal such as a flying squirrel one sees significant 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 essentially has a loose flap of skin that stretches between its front and hind legs. The birds and bats can control and alter the shape of their 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 using the energy they have stored from the height at which they jumped. Although they do have some maneuverability it is quite limited by comparison to birds and bats.

Birds and bats have powered flight and hence not only have vastly improved maneuverability over animals like the flying squirrel, but they have the ability to sustain flight for long durations. While flying squirrels can use their gliding ability to escape danger or to move from tree to tree, bats and birds use their flight skills for much more. They certainly use flight to escape danger and transportation over short distances, but they also use flight for hunting and other food gathering, finding mates, and seasonal migrations to name a few. In other words, their entire lives are built around flight since their bodies are totally adapted to flight. Most likely, since the adaptations to flight for the Pterosaurs was just as thorough as for birds and bats that they too were totally adapted to flight and their lives revolved around flight. Flying squirrels on the other hand, live in and around trees but don't use flight except when necessary. Their primary adaptations are for their life in trees, not for flight. Gliding suits them well. They don't use flight to hunt, migrate, find a mate, just on the occasions that they need to go from tree to tree.

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 regiment in order to save energy and to be able to stay 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 aspect ratio, 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 alights on the water it will have a very difficult time getting airborne again, if it lands on flat land with no cliffs to jump from it will also have a difficult time getting airborne. When at sea it obtains food by flying low and slow and scooping it prey with its beak. Yet the frigate bird will stay aloft over water for many hours. If it were to stay airborne by flapping its wings to stay aloft it would consume energy at a high rate, resulting in a very short time at sea. However, as mentioned earlier the frigate bird can stay at sea for great lengths of time. It is able to do this by soaring 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, one can imagine that a pterosaur with apparently similar traits living in a similar manner. Its not difficult to imagine the Pteranodon living and roosting on cliff tops, jumping to get airborne, and spending the day soaring. When it spots prey, most likely fish, it swoops low and slow until it catches the fish with its jaws, all the while remaining airborne. Then consuming it and returning to its dwelling and sharing its meal with its young. The similar shapes and similar life styles, of the frigate bird and Pteranodan 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. Birds generally have a wing with a cross sectional shape of a common airfoil as used on aircraft. A rounded nose, relatively flat on the bottom, and a curved upper surface tapering to a thin point in the rear. This shape is achieved by a combination of the bony structure of the wing, the skin and muscle tissue of the wing, and the feathers overlaying the wing. A similar cross section of a bats wing will yield a wing slightly different, basically a cambered airfoil shape, that is, a wing which is a flattened semi-circular curve where the upper and lower surface follow the same shape. Both the bats wing and the birds wing provide lift and are very efficient for powered flight. Although there are differences and generally perhaps the bats wings are better adapted for slow flight birds for faster flight, they both are efficient wings.

In addition to the fossils found of Pterosaurs impressions of their wings and bodies have also been found. These impressions were apparently left in the mud where the animal died and have been included in the fossil record. The impressions indicate that the Pterosaurs had membrane type wings similar to bats, but longer and narrower similar to birds. Basically a cambered airfoil shape but with wing areas and aspect ratios similar to birds. The impressions also indicate that the "membrane" structure had a fibrous or muscle structure to it. All this leads to the conclusion that the Pterosaurs generally had membrane type wings, but with sufficient supporting structure to make the wing taught or on the rigid side. This drives the conclusion that the airfoil of the Pterosaurs allowed for precise flight control as in modern birds and bats. It tends to counter the argument that they were "failures at flight" as some have speculated. And it tends to lead to the conclusion that Pterosaurs were quite accomplished flyers.

A plane view (view looking down from above) of the wings of birds, bats, and Pterosaurs also adds to the understanding of their ability to fly. Some key aspects of the shape of a wing are its span (width), chord (front to back thickness), and its area. The aspect ratio is the ratio of the span to the chord. Typically, a wing with a high aspect ratio, a large span relative to a small chord is good for gliding. Whereas a low aspect ratio wing is more a maneuverable wing. Examples of a high aspect ratio wing would be the albatross as a bird, or the U-2 as an aircraft. Low aspect ratio wings can be found on starlings and eagles or on an aircraft such as the F-15. Controversy exists as to where the back of the wing attached on Pterosaurs, that is, did the back of the wing attach to the body leaving the legs free, or to the legs themselves as in bats. The difference being that attaching to the body produces a higher aspect ratio and attaching to the legs produces a lower aspect ratio. Yet, either way the aspect ratio of Pterosaurs is in the same range of birds and higher than that of bats. The implication is that the wings of Pterosaurs allowed the same type flying as modern flyers. The range of aspect ratios of the different Pterosaurs were in the range of modern birds which means that they could have been thermal soarers and others slope soarers. Thermal soarers are those birds which glide and maneuver in rising thermals like eagles. Whereas, slope soarers are those which glide in winds which form on an up slope or along waves, sea gulls and the albatross are examples of this. It seems likely that Pterosaurs probably had adapted to both thermal and slope soaring given the range of aspect ratios of their wings and the locations of their fossils.

Body Structure

Typically the Pterosaurs had a relatively short and stout body structure relative to its overall size. Like modern birds, its chest and back area in the vicinity of the wings had bone structure, breast bone, which allowed for secure anchorage for 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, due to the extended snout was typically very long, and in some species was as long as or longer than the body. The Pteranodon, for example, had a crest on its head which extended back almost as far as the snout forward. The overall length of its head from the tip of its snout to the end of its crest was longer than the length of its body (torso). Its neck was long and seems to have been quite maneuverable allowing the head to be moved as needed to snag prey.

Pterosaurs also had a short upper arm, a longer forearm, with the outer half of the wing structure being made up of bones from the little finger. The other three fingers extended outward at the joint where the big finger and the forearm met. These three fingers ended in claws. Speculation is that the Pterosaur was quite able on the ground as well as in flight. Their mobility on the ground is based upon how it could have folded its wings and walked on it hind legs and three fingers on its front arms (wings).

In examining fossil bones of the Pterosaurs the lightness of body structure becomes apparent and is quite amazing. Most of the bones in the Pterosaurs were hollow with light reinforcing structure in critically stressed areas. Because of holes found in the bones, it is believed that these bones were hollow, not marrow filled, with air sacs as in modern birds. In examining and comparing these bones with modern birds bones, the Pterosaurs bones were very light. In fact, it is believed that a Pterosaur would be considerably lighter than a modern bird for the same size animal.

From examining the fossil remains the attachments for powerful muscles appear to be present. This is in keeping with what a Pterosaur would need to sustain powered flight. Even soaring birds do sustain powered flight until they find rising air currents and hence, they too need significant muscle structure to power their wings. The smaller Pterosaurs which were probably not soarers but rather conventional flyers such as smaller birds, sparrows and pigeons, truly needed considerable muscle structure for powering their wings. With the fossil indications of anchorage's for muscles and tendons, our understanding of powered vertebrate flight, and educated guesses, it seems likely that the muscle structure of Pterosaurs was every bit as involved and complex as modern birds and bats, and indeed quite similar.

We can continue to come up with a list of other features that Pterosaurs were likely to have in order to be successful as flyers. An important point is that we are assuming that they were successful flyers. If we assume that they were not successful flyers, we would be looking at the evidence differently and would need to explain how something not successful could have survived for 157 million years. Now that we know the skeleton of the Pterosaur from the fossils and from examining it we can postulate the presence of powerful muscles. From its shape we can postulate its life style or a least derive clues from what we feel are its modern equivalents, birds and bats. Assuming it was a successful flyer and had powerful muscles, we can make the assumption that it most likely was endothermic or warm blooded. This argument is logical since the type of energy necessary to sustain flight for both active flyers and soarers is substantial. In addition, since the entire creature is designed around light weight and hence efficiency it stands to reason that its muscles would also be reasonably efficient. For sustained muscle power and powered flight a creature defined as warm blooded seems to be a necessity. That is, the ability to regulate its body heat efficiently. When the environment is cool, it can generate heat from its muscles, and when the environment is too hot, it can shed excess heat to keep from overheating. Very little direct evidence exists as to biological clues of warm or cold bloodedness in pterosaurs or for that matter dinosaurs, therefore indirect evidence and speculation are the main avenues for theory. Since all birds and bats are endothermic and a great many similarities exist, it is reasonable to speculate on the warm bloodedness of the Pterosaurs.

Assuming that the Pterosaurs were warm blooded or something equivalent, then comes the issue of insulation to allow the 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. From the impression left in the fossil record the covering on Pterosaurs seems to have derived from scales to something similar to feathers, but not quite feathers. Yet it probably had similar insulation properties to feathers. Although the evidence shows that the body had this feather like covering, no fossil evidence would put any of the feather like covering on the wings. All 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 type structure. This is very similar to the arrangement found in bats today. This is another indication that the formula for flight which the Pterosaurs developed is similar to the modern equivalents.

Another issue is speed of flight. Once again speculation is relied upon due to the lack of direct evidence. The Pterosaurs developed different classes to fit different environmental niches and needs, as do both modern birds and bats. Birds have developed wings which cover all ends of the spectrum, from the very slow to the very fast and everything in between. The largest flying birds are relatively slow, but can soar for long periods of time, where as 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 also have their slow graceful representatives and their fast ones. They also have those who can effectively hover to get at nectar in flowers. The fossil evidence indicates that some Pterosaurs were soarers and hence relatively slow while others probably were relatively fast. Since Pterosaurs had seemingly frail skeletons they most likely limited their airspeed to speeds which were appropriate for the strength of their bodies structure. Pterosaurs too seem to have covered the entire speed range of flight.

Conclusion

The evidence is good, though speculative, that Pterosaurs during their reign as the dominant, perhaps only, flyers were well developed flyers and had filled all niches of the environment. They were indeed successful, highly successful, and survived for 157 million years which is no small feat. Interestingly, vertebrate flight has certain rules such as shape, lightness of body structure, energy production and efficiency which all flying vertebrates must follow. The Pterosaurs were no exception, merely the first to fly.

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