Dragons Of The

The dragon blinked in the fierce light of the sun as it emerged from the clouds and banked hard, its tremendous wings arching under the load. Reflected in a massive dark eye, the world below slowly tilted into view. Vast herds of dinosaurs were strung out across a dusty yellow-orange plain, occasionally gathered in knots where they had stopped to feed on patches of stunted vegetation. Then came marshes and— the dragon focused— a long, still, clear-blue lake. In its glassy depths, rainbow-hued fish hung almost motionless in the warm water, fins undulating, gills slowly pulsing. Suddenly, a huge dark shadow swept across the water's surface and, before it could dive into the safety of the weeds, a fish was gripped by long, sharp-pointed jaws and jerked violently into the air. As its consciousness faded, it gazed up into a limpid eye, set in a reptilian skull framed by fine, straggly hair. Slender, powerful wings beat smoothly up and down, membranes tensed and relaxed as the animal rose swiftly. At the top of its climb the Quet%alcoatlus paused, swallowed, then dived down again toward the shimmering lake far below.'

FIGURE 1.1 A beautiful new fossil of the Upper Jurassic (approximately 148 million years old) Solnhofen Limestone pterosaur Anurognathus, only the second example yet known for this species. This pterosaur had a wingspan of about 16 inches (40 centimeters). (Photograph courtesy of Helmut Tischlinger.)

Around 215 million years ago, at about the same time as dinosaurs first spread across the continents, an altogether different group of reptiles took to the air. Reptiles had tried this before, on several occasions, but this time was different. This time they got beyond gliding, where all previous groups had given up, and, as bats and birds were to do millions of years later, they evolved a rare and complex adaptation: true flapping flight. Going boldly where no reptile had gone before, these intrepid aeronauts entered a new realm— the open sky— and developed into a riotous multitude of species. Some, such as the frog-headed beetle-cruncher Anurognathus, shown in Figure 1.1, were as small as a starling, but others, like Quet%alcoatlus, became as large as an airplane. They thrived for 150 million years, only to disappear forever in the events that also killed off many of their contemporaries, including, most famously, the dinosaurs, and brought evolution's finest hour, the Mesozoic, to a close. This extraordinary group of animals— nature's real dragons— was the pterosaurs.2

The Trouble with Pterosaurs Pterosaurs, "winged reptiles," as their Greek name puts it, are familiar to most people as rather fierce-looking, leather-winged monsters featured in classic novels, such as Arthur Conan-Doyle's Lost World, or flit across the screen in TV documentaries3 and in movies from King Kong to Jurassic Park.' No dinosaur scene is complete without them— usually a Pteranodon, the most famous pterosaur of them all, with large teeth to give it added fierceness, even though this species was actually completely toothless.5 Trying to see beyond these superficial images and get a glimpse of the real thing triggers all sorts of questions: What were pterosaurs really like? How big did they get? Could they fly as well as birds? And one of the first questions that is always asked and hardest to answer: Why did they become extinct?

Driven more than most by curiosity, scientists find these strange creatures absolutely fascinating (pterosaur talks always fill the hall at scientific meetings) and some of the sharpest paleontological minds ever to ponder a fossil were so beguiled by these extraordinary animals that they made them the centerpiece of their researches. The first thing they discovered was that pterosaurs are really hard to understand. Even the term embodied in their name— winged reptile— seems contradictory. The word reptile, from the French "repere," meaning to creep, is not especially flattering, but describes living reptiles rather well. Wings, on the other hand, are about the last thing one might expect such a creature to have, and yet for pterosaurs, this defined them and their very existence.

As soon as pterosaurs were discovered, at the end of the 18th century, naturalists started quarrelling about them. Disagreements came thick and fast: Pterosaur origins, for instance, were hotly debated on several occasions, and, in one particular case detailed in Chapter 4, led to a protracted and acrimonious feud, while several other disagreements, for example, over wing shape and walking posture, continue even now. It was a long time before scientists could even agree as to what kind of animal pterosaurs might be— reptiles, as it turned out, but others argued that they were birds, and several eminent naturalists became convinced that they were bats. Debates also raged over the lifestyle of pterosaurs. Were they some kind of water creature? Or could they fly? And what did they do on the ground— strut around on their hind limbs like birds, or clump around on all fours? Even their likely metabolism became a scientific battleground: cool-blooded like crocodiles and lizards, insisted several authorities, warm-blooded like birds and mammals, countered others.

Pterosaurs became a cause celebre, one of the great paleontological mysteries. Each generation of scientists "had a go" at them, and everyone had an opinion that, almost without exception, differed from that held by everyone else. The arguments, the confusion and the misunderstandings continued right up until a decade ago, and a few persist even today, but before we get into that, we should look a little more closely at why these ancient fliers caused so much controversy in the first place.

A Fossil Problem Pterosaurs have successfully defied more than two centuries' worth of scientific probing for several reasons. The most obvious is the problem of trying to understand animals that are known only from fossils. Just a tiny proportion of all the pterosaurs that ever existed, probably less than one individual in a million, has actually made it into the fossil record. The processes by which their cadavers became fossils, normally survived only by the hardest parts of the body— bones and teeth6— mean that most of the important information about anatomy, movement and behavior, how pterosaurs were colored, what noises they made, was lost forever.

Compounding the problem, even pterosaurs' hard parts were not well-suited for the rigors of fossilization. Pterosaurs were creatures of the air, with a relatively light and delicate skeleton constructed from slender, hollow bones whose walls were often little thicker than a credit card. This is not a good design if you want to become a fossil. To begin with, it meant that even pterosaurs' skeletons were relatively easily destroyed, so, compared with other backboned animals, their fossil remains are rare. Worse still, if you pull open a museum drawer, you find that most of their fossilized remains consist of isolated, often broken, bones— dumb witnesses that tell us little more than "here be pterosaurs." To cap it all, most of the decent pterosaur fossils that we do have, whole skeletons and, very occasionally, fragments of fossilized soft tissues, come from just a few locations scattered across the world and are separated by vast, barren, pterosaur-less gaps of thousands of miles and millions ofyears.

Thin-walled bones also mean that the complete skeleton of Anurognathus, shown in Figure 1.1, buried at the bottom of a Bavarian lagoon 148 million years ago, is rather less helpful than one might expect. Like many other beautiful-looking pterosaurs, several of which are featured in this book, it is absolutely flat— a "picture" fossil— its hollow-tube bones unable to resist the inexorable crushing weight applied over countless millennia by the overlying rock. Without the three-dimensional, sticking-out-here, dimpled-in-there form of the skull, the pelvis, or any of the 300 or so bones that made up a pterosaur skeleton, and unable to measure the exact shape, size and position of the joints, paleontology is robbed of critical data.

Confronted with a row of these "road-kills," it is often hard for an observer to establish even basic facts, such as: How many species are there? Two? Or more? Or just one, its representatives flattened in different ways? Trying to go further and find out, for example, how these pterosaurs might have stood, walked, or flown, is even harder. Strictly speaking, these are relatively simple questions (some of the really tough ones, for example, about physiology and breathing, will pop up later), but, enigmatic as the Mona Lisa, and sometimes just as smiley, the "picture" pterosaurs rarely give an answer.

More Problems: Analogy and Chauvinism As if fossils themselves were not difficult enough to interpret, the ways in which scientists have gone about studying them also have their pitfalls. One trap that pterosaur researchers seem to have queued up to throw themselves into is a method much used, and no less often abused, by paleontologists: analogy. Confronted with the fossilized remains of an organism from deep time— be it a tiddly little ammonite, a 10-ton dinosaur or a toothless Pteranodon, all extinct for half an eternity and tragically bereft of any living descendants— it is terri bly tempting to reach for analogy. Essentially, this means choosing a living organism that, although completely unrelated to ammonites or dinosaurs or even pterosaurs, seems to be sufficiently similar to them in external appearance or supposed lifestyle that we can use it as a mental vehicle for trying to better understand those long-expired denizens of the past.

In the case of pterosaurs, one does not have to look far (just upward) to spot their living analogies: birds and bats. Often bolstered by the mistaken belief that pterosaurs were somehow related to one or the other, scientists have repeatedly tried to use these modern fliers as models for understanding the flying reptiles. Yet, time and again, birds and bats proved to be treacherous allies. Similarities apparent in all three aeronauts— compact bodies, large wings, lightly built skeletons— were not inherited from a common ancestor, but result from convergent evolution. That is, the features that these fliers share evolved quite independently in each group as a response to the same difficult and highly demanding activity— flight.

Put them under the spotlight, though, and these three groups are found to be quite different. Pterosaurs, as the fossil in Figure 1.2 shows, had a membrane wing, the outer part ofwhich was supported by a single extraordinarily long and robustly built finger (hence, the vernacular name "pterodactyl," meaning wing-finger). Bats also have a membrane wing, but its outer part is supported by not one, but four fingers that, while long, are relatively thin and spindly. Birds, by contrast, have feathered wings, and their fingers (compared with pterosaurs and bats, at least) are strongly reduced.

The message is clear: pterosaurs were not birds or bats, nor were they related to them. Bitter experience has taught researchers to avoid the beguiling analogies offered by living fliers and to rely on the fossil remains of pterosaurs themselves as the best means for unraveling the mysteries of these animals.

A second pitfall, chauvinism, is rather more subtle, but no less dangerous. A widespread misperception of the living world is that organisms alive today are somehow "better" than those that existed in the past. Bombarded as we are by advertisements to buy the latest, fastest, shiniest whatever, it's easy to see why this notion is so pervasive. This "temporal chauvinism" is closely bound up with another misleading idea: that organisms can be ranked as if on a ladder, with the simplest forms of life on the bottom rung and the most complex and important— man, obviously (or even more meretriciously, certain races of man)— on the top rung. This is all complete hogwash, as that late great dispeller of such myths Stephen J. Gould has so effectively

Mongol Wing Patches

figure 1.2 "Dark-Wing" Rhamphorhynchus. This fantastically well-preserved Upper Jurassic fossil, seen here in ultraviolet light, has one of the best preserved pterosaur wing membranes ever found. With a wingspan of about 3 foot (1 meter) in life, this specimen was first described by Helmut Tischlinger and Dino Frey (2001). (Photograph courtesy of Helmut Tischlinger.)

figure 1.2 "Dark-Wing" Rhamphorhynchus. This fantastically well-preserved Upper Jurassic fossil, seen here in ultraviolet light, has one of the best preserved pterosaur wing membranes ever found. With a wingspan of about 3 foot (1 meter) in life, this specimen was first described by Helmut Tischlinger and Dino Frey (2001). (Photograph courtesy of Helmut Tischlinger.)

shown in his writings, but nineteenth-century science was riddled with such ideas and, though now more subtle, they survive even today, lurking in the much debated notion that evolution is always progressive.'

Pterosaurs, like many other groups, such as dinosaurs and, closer to home, Neanderthals, have been innocent victims of this chauvinism. Obviously, such primitive-looking leather-winged lizards were an early but doomed attempt at flight and clearly inferior to birds and bats. Otherwise they would still be around, wouldn't they? A double whammy— temporal and biological chauvinism ganging up together. Generally speaking, of course, such a caricature, though it still exists and can even be found in the scientific literature, is a relatively trivial problem. The real difficulty is that such ideas can hinder scientists from grasping the true nature of the fossil organisms with which they are dealing, be it pterosaurs or any other extinct group, because, right from the start, they ensnare the victims (both object and observer) within a false and misleading perspective.

in fact, contrary to our often unthinkingly biased expectations, the latest scientific findings suggest that pterosaurs living 100 million years ago may have been more efficient fliers than the birds and bats that fill our skies today8— a poke in the eye for our self-centered human chauvinism.

Solving the Pterosaur Puzzle Fettered by a patchy fossil record, misleading analogies with birds and bats and a chauvinistic milieu, it's not surprising that the true nature of these Mesozoic dragons has proven so elusive— until now. A glut of new finds, including some extraordinarily well-preserved wing membranes (illustrated in Figure 1.2), thousands of fossilized tracks of pterosaurs (shown in Figure 1.3) and, for my money the most thrilling of all, an embryonic pterosaur in an egg, are finally laying bare some of the greatest mysteries of these enigmatic creatures. No little help has been provided by novel techniques and technologies such as CAT scanning,9 which permits researchers to look inside pterosaur skulls (a view reproduced in Figure 1.4), allowing them to squeeze the last drops of information out of fossil finds, both old and new.

Rather like cresting the top of a hill and seeing a marvelous panorama for the first time, when all these new discoveries are put together, they reveal a startlingly new but also remarkably coherent and convincing picture of

FIGURE 1.3 Scuttling around on a beach about 150 million years ago, pterosaurs left impressions of their hands, feet, and what seem to be beak marks in sands that subsequently became a layer of stone, now broken up into boulders to be found lying on the sea shore in the Asturias region of northern Spain. (Image courtesy of Jose Carlos Martinez Garcia-Ramos and Laura Pinuela.)

FIGURE 1.4 Inside a pterosaurs' head. This image, prepared from a Computer Automared Tomographic (CAT) scan of the skull ofRhamphorhynchus, shows a vertical slice about 4 inches (10 centimeters) long running through the middle of the skull, from the front (right) to the back (left), with bones colored purple and a reconstruction of the brain in green. The large opening in the rear half of the skull housed the eyeball. (Image courtesy of Larry Witmer.)

FIGURE 1.3 Scuttling around on a beach about 150 million years ago, pterosaurs left impressions of their hands, feet, and what seem to be beak marks in sands that subsequently became a layer of stone, now broken up into boulders to be found lying on the sea shore in the Asturias region of northern Spain. (Image courtesy of Jose Carlos Martinez Garcia-Ramos and Laura Pinuela.)

pterosaurs. The best way to explain how this breakthrough was achieved is with a metaphor.

imagine that you have been given a large box containing a jigsaw puzzle with many thousands of pieces. When completed, the picture reveals how pterosaurs were constructed, how they walked, flew, fed and grew, even how they evolved over their 150-million-year history. Now, without looking at them, take most of the pieces out of the box and throw them in the fire. Those were all the species, anatomy, behaviors and events that didn't make it into the fossil record.

The handful of pieces that remains represents pterosaur fossils buried in rocks scattered across the seven continents and, in some cases, under the sea. The first problem for paleontologists has been to get a few of those pieces out of the box, that is, collect some fossils— not always easy when they lie buried in the ground in remote regions of Earth, such as western Mongolia, for example. The next challenge has been to try to examine most of the available puzzle pieces, now to be found in fossil collections all over the world, decipher what it is that they seem to show, be it a feature of the brain or a trail of footprints, and then fit them together in a way that, we hope, matches up to some part of the original, true picture.

using the puzzle metaphor, we can readily grasp how extraordinarily difficult it must have been 200 years ago for the first naturalists who tried to comprehend pterosaurs with the equivalent of just one piece of the puzzle in their hands. Even so, the legendary French anatomist Baron Georges Cuvier, the great-grandpere of all pterosaur researchers, was spot on when he proposed, in 1801, that pterosaurs were flying reptiles.10 Slowly, over the decades, more and more pieces of the puzzle— fossil finds in Europe and then in the Americas, Africa and Middle Asia, and finally in China and even Antarctica— came to light.

Still, even by the late 20th century, several critical puzzle pieces— such as the design of pterosaurs' wings: broad or narrow? Their walking ability: on two legs or four? Their physiology: like reptiles or birds?— remained, well, puzzling. Just as perplexing, no matter how much one rearranged them, there were always points where the pieces that we had already collected just would not match up. So, for example, while one study concluded that pterosaurs could not have used their arms for walking, another described clear, well-preserved handprints in the tracks of these animals (this paradox is resolved in Chapter 9).

Then, in just a few years, beginning in the mid-1990s, the puzzle suddenly came together and revealed a consistent and convincing picture of pterosaurs, their lives and their fate. But why then and not before? If we step back a couple of decades to the time in the 1970s when modern vertebrate paleontology (the study of extinct backboned animals, including pterosaurs), was just getting under way, we find that among its many new interests was an age-old problem: the pterosaurs. Ground-breaking work in those early years by the Munich-based paleontologist Peter Wellnhofer, the world's leading authority on these animals, eventually attracted the attention of a whole new generation of researchers and triggered a tidal wave of research that "broke" in the 1990s but even now, in mid-2005, shows no sign of abating. In the past two decades, "pterosaurology," as we might now refer to the study of pterosaurs, has seen more fossils collected, more techniques brought to bear and a greater volume of scientific studies and publications than ever before.

The jigsaw puzzle is still far from complete, but we have enough pieces to make out the picture, and it seems at last to make some sense. This book puts that picture on display for the first time and, as with any good exhibition, there are lots of surprises.

Rulers of the Mesozoic Skies Pterosaurs, as the sketch in Figure 1.5 shows and the following chapters will reveal in glorious detail, were completely different from any other animal, living or extinct. They were reptiles, but, unlike lizards or crocodiles, they were not scaly (except perhaps on the legs and soles of the feet), but furry,11 and, unlike their "cold-blooded" reptilian relatives, they seem to have been capable of strenuous and protracted exercise, such as flapping their wings, for hours on end, something that in the modern world only warm-blooded animals can do. Equipped with relatively large bird-like brains, they also appear to have been much more intelligent than living reptiles and, if the spectacular and astonishingly diverse range of "look at me" head crests is anything to judge by, they also had complex social behaviors.

Above all else, pterosaurs were creatures of the air. Their entire bodies were highly modified for flight, powered by a warm-blooded physiological engine and lungs that may have been as efficient as those of birds. Pterosaurs also appear to have had highly sophisticated flight membranes that were directly connected to the brain— clever wings that may have been better than

FIGURE 1.5 Child of the revolution. A restoration of the Upper Jurassic, crow-sized pterosaur Pterodactylus based on the latest information and ideas regarding pterosaurs' soft-tissue anatomy. (Redrawn from Dino Frey et al., 2003.)

FIGURE 1.5 Child of the revolution. A restoration of the Upper Jurassic, crow-sized pterosaur Pterodactylus based on the latest information and ideas regarding pterosaurs' soft-tissue anatomy. (Redrawn from Dino Frey et al., 2003.)

Bird Antaomy Wingspan

anything to be found in modern aeronauts, natural or man-made. Consequently, these Mesozoic dragons are now envisioned as highly competent and vigorous fliers, capable of snatching up their prey while on the wing and of staying aloft for hours or even days at a time. Indeed, the latest studies (reported in Chapter 9) suggest that some aspects of flight performance, such as the soaring ability of Pteranodon, a highly specialized albatross-like pterosaur, may have outstripped that of any living bird.

The ground, however, was quite a different matter. With their legs fastened to each other and to their arms by the flight membranes, long-tailed rhamphorhynchoid pterosaurs were rather hampered in their movements and probably kept out of harm's way by clinging to trees or cliffs using long, strongly curved claws on their fingers and toes. By contrast, short-tailed pterodactyloid pterosaurs evolved somewhat narrower flight membranes that gave their legs more freedom and endowed them with the ability to scamper around rather more adroitly. Having "conquered" the ground, pterodacty-loids were able to exploit all kinds of new life styles. Many of these involved

FIGURE 1.6 A tiny pterosaur tragedy. This individual ofPterodactylus, from the Upper Jurassic Solnhofen Limestone of Bavaria, at only 8 inches (20 centimeters) in wingspan, was probably only a few days or weeks old when it died, perhaps after an accident on one of its maiden flights. (Photograph courtesy of Helmut Tischlinger.)

FIGURE 1.6 A tiny pterosaur tragedy. This individual ofPterodactylus, from the Upper Jurassic Solnhofen Limestone of Bavaria, at only 8 inches (20 centimeters) in wingspan, was probably only a few days or weeks old when it died, perhaps after an accident on one of its maiden flights. (Photograph courtesy of Helmut Tischlinger.)

wading in ponds and streams and, as they stumped around in a uniquely pterosaurian fashion, rather like a saddle-worn cowboy on crutches, they left behind their peculiar "feet before the hands" tracks imprinted on mud flats and seashores all over the world.

Not content with merely looking different, pterosaurs also appear to have been unique among flighted animals in that they adopted a "hands-off" approach to bringing up their young. Almost without exception, hatchling birds and baby bats are looked after by their parents and must be almost fully grown before they can take to the air. Astonishing as it may seem, baby pterosaurs like the one shown in Figure 1.6 could fly soon after hatching and may not have needed or received any assistance from mom or dad. Interestingly, this remarkable ability might help explain another unique and spectacular feature of pterosaurs: gigantism. They were equipped with the unique property of being able to grow and fly and it would seem that pterosaurs were not restricted to a particular size but, in some cases, just continued growing until they were as big as an airplane.

The unique construction, abilities and behaviors of pterosaurs paid off— big time— and the group became tremendously successful. This is seen, for example, in the remarkable diversity of these animals, with forms ranging from agile, aerial insect hunters, through flamingo-like filter-feeders with thousands of teeth, to highly evolved ocean-going soarers. They also achieved an incredible range of sizes: While the smallest was only about 20 centimeters (8 inches) in wingspan and probably weighed less than a starling, the largest had wings more than 10 meters (almost 40 feet) from tip to tip and probably tipped the scales at around 50 kilograms (110 pounds) or more. Pterosaurs were successful in other ways, too. After they first appeared about 215 million years ago, it did not take them long to spread around the world, after which they dominated the skies for the next 150 million years. That is more than twice the length of the known history of bats and rivals the evolutionary longevity of birds.

Why Pterosaurs? Prehistoric reptiles are big business. Every day thousands of books detailing the lives and deaths of Tyrannosaurus, Diplodocus and a host of their dinosaurian relatives are sold across the world, and literally millions of viewers tune in to the latest TV documentaries to catch the breaking news from the Mesozoic. Huge, weird, dangerous-looking monsters from the deep past excite, fascinate and entrance people of all ages everywhere and, thanks to their extinction long ago, these creatures are a "safe" thrill. But, just as in the past, dinosaurs rule. Other denizens of the dinosaurian world such as ichthyosaurs and plesiosaurs— toothy killers that swam the Mesozoic seas— are occasionally allowed to show their faces, but whole TV programs or entire books devoted to these animals are still rare.

It is the same with pterosaurs. There is no doubting the extraordinary appeal these incredible creatures exert on the imagination of anyone who glimpses them on a TV screen or billboard, but until now, if you wanted to read more about them, it wasn't easy. The first book on pterosaurs, Dragons of the Air, written by the English paleontologist Harry Seeley, appeared in 1901, more than 100 years after pterosaurs had first come to light. Rare, expensive and completely out of date, this marvelously idiosyncratic work is still a literary delight. Having read it, though, readers had to wait another 90

years for a second book on pterosaurs— Peter Wellnhofer's magnum opus The Illustrated Encyclopedia of Pterosaurs. Chock-full of information on every pterosaur species known to science in 1991, this was the principal reference volume for the group but, like Dragons of the Air, it, too, is now out of print, rare and expensive.

Much has changed since the Encyclopedia first appeared. The many critical ideas about pterosaur biology that were fought over in the 1990s— Were they two- or four-footed on the ground? Did the flight membranes attach to the legs? Did they leave tracks— have been resolved into a convincing and (among pterosaurologists) widely agreed-upon picture. At the same time, a stream of new fossil discoveries (more than 30 pterosaurs previously unknown to science have been described since the Encyclopedia was published) and the application of modern techniques, for example, with regard to discovering pterosaur genealogy, have dramatically improved our knowledge of the evolutionary history of these animals.

The pages that follow contain the first comprehensive account of our new understanding of how pterosaurs were constructed and how they lived their lives: how they flew, walked, breathed and grew. What this book also reveals, for the first time, is how the design and function of these animals launched their successful invasion of the skies and also shaped their final doom.

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