Tree For Pterosaurs

Shaded from the glaring sun beneath the canopy of several tree ferns, insects whined and hummed in the stifling heat of yet another cloudless Triassic day. A large, metallic green dragonfly, wings whirring, detached itself from the tip of a dead twig and began its patrol back and forth, occasionally darting from its path to grab some slow-flying victim. Returning to its perch, it dismembered its prey, then swooped back into the air— lord of the skies, the biggest thing on the wing. At (east, until now. Higher up, above the dragonfly, deep in the shadows of the massive fronds, hung something quite a lot bigger. It had watched the green hunter on its sentinel beat, and now it was unfolding short, broad wings, its legs were tensing, and down it came, in a rush of membranes, a swish of a tail and a lot, such a lot, of needle-sharp teeth. The dragonfly flickered its wings and sped away from the path of this tumbling threat toward the edge of the canopy shade and the safety of the open sky. Except that safety was now full of more membrane-winged fliers, one of which bit the dragonfly in half as the others fanned out in search of more victims. Towered by a rich diet of insects, protopterosaurs had really taken to the air:

FIGURE 4*1 Could this early, sparrow-sized gliding reptile, Sharovipteryx from Upper Triassic rocks of the Fergana Valley in Kirgizia, be ancestral to pterosaurs? Probably not, because it is almost the same geological age as early pterosaurs and, with its remarkably long neck, already highly specialized. Still, it might have something important to tell us about how pterosaurs first took to the air.

Naming Names Before plunging into the heart of pterosaur biology, a little familiarity with the family tree is required. Pterosaurologists have toiled long and hard to discover the genealogy of these animals, identifying and naming species, linking them together into their natural clans and tracing out the relationships between one clan and the next, until all are linked together in a complete family tree.

Before such a grand classification scheme could be drawn up, however, came the task of identifying and naming the basic components from which this tree was made— species. According to the generally accepted definition, a species, including the one to which we belong, Homo sapiens,2 consists of a group of individuals (often totaling several million or more) that can successfully interbreed with one another, but not with members of other species, to produce offspring that are themselves capable of reproducing.3 While, in theory, one could test the members of living species to see if they fit this definition, it is impossible to observe the breeding behavior of fossils, so paleontologists rely on another aspect of extinct species in order to identify them: Their members look more like each other than members of other species.4 And that, basically, is how pterosaurologists have recognized, defined and named the approximately 100 species ofpterosaur discovered so far.5

Among pterosaurs (and many other backboned animals), features that best distinguish species— their hallmarks— are generally to be found in the anatomically most complicated part of the body: the skull. The basic design of this structure and, in toothed pterosaurs, details of the teeth, such as their shape, relative size, spacing and arrangement, are usually sufficient to distinguish species at a glance. Features of the limb bones, especially their relative lengths, can also be helpful, although they tend to be typical of larger clans (genera and families, for example) rather than particular species.

As each new fossil comes to light, it is compared with those found previously to see whether it belongs to an existing species of pterosaur. Usually it does, but when it doesn't, a new species must be defined, named and described— a process that lies at the core of the science known as taxonomy.6 Often, the formal scientific names given to pterosaurs refer to distinctive parts of their owners' anatomy. In the case of Pteranodon longiceps, first proposed in 1876 by Professor Othniel C. Marsh of Yale University for a pterosaur that had been found in the Upper Cretaceous chalk bluffs of Kansas, the genus name Pteranodon, meaning winged and toothless, is remarkably apt, while the specific epithet longiceps perfectly describes the extraordinary development of the jaws.7

Many pterosaur names contain a reference to the location where the fossil on which they are founded was first discovered. Dsungaria and Zhejiang, both in China, gave us Dsungaripterus and Zhejiangopterus. These names also illustrate another tradition of pterosaur taxonomy, the inclusion, in modified form, of the Greek term "pteron," which means wing, alluding to the aerial mode of life of these animals. My favorite tradition with regard to the concoction of pterosaur names is the references made to dragons, spirits and gods. Take, for instance, A%hdarcho, from the Upper Cretaceous of middle Asia, a memorable moniker that stems from the Uzbek word for dragon, or Tapejara, an ancient Brazilian spirit, and perhaps the most evocative pterosaur name of all, Quet%alcoatlus, derived from the Mexican deity Quetzalcoatl, the plumed serpent. (A complete list of all valid pterosaur names can be found at the back of this book.)

Pterosaur taxonomy never sleeps. As new, more complete, or better-preserved fossils are found, they are compared with previously named species, while, in turn, these "older" species are reassessed in light of the new finds. Sometimes, one or more fossils may be split away from their original species to form a new species. Much more commonly, taxonomists will take several supposedly different species and lump them together under a single name.8 The difficulty with pterosaurs, as indeed with most animals and plants, is that while members of a species are supposed to look like one another, they may, in fact, appear quite different. This can happen for several reasons. Natural variation, especially in size, is common in adult reptiles, and pterosaurs are no exception. Differences between the sexes can also be striking, especially when one or the other is ornately decorated, as in many birds, for example, most spectacularly, the peacock. Age can also have a profound impact on appearance. With their relatively large eyes and short limbs, youngsters may look quite different from their parents and, as has happened on several occasions for pterosaurs, if their immaturity is not recognized, they could be misidentified as members of a "small" species.

This problem of variability has long plagued pterosaur taxonomy and, as recent studies have shown, youngsters and adults, males and females have often found themselves in completely different species. Painstaking taxonomic work has helped to reunite many of these strays with other members of their own species. As Figure 4 . 2 illustrates, what for many years were thought to be five distinct species of Rhamphorhynchus have now been recognized by the American pterosaurologist Chris Bennett,9 based at Fort Hays University in Kansas, as five stages in the growth of just a single species: Rhamphorhynchus

Hays Kansas Pterosaur

FIGURE 4*2 Until recently, these skulls were thought to represent five different species of the long-tailed Late Jurassic Solnhofen Limestone pterosaur Rhamphorhynchus. Work by Chris Bennett (1995) has demonstrated that they are in fact just different growth stages of a single species: Rhamphorhynchus muensteri. (Redrawn from Bennett, 1995.)

FIGURE 4*2 Until recently, these skulls were thought to represent five different species of the long-tailed Late Jurassic Solnhofen Limestone pterosaur Rhamphorhynchus. Work by Chris Bennett (1995) has demonstrated that they are in fact just different growth stages of a single species: Rhamphorhynchus muensteri. (Redrawn from Bennett, 1995.)

muensteri. Features such as the degree of unification of the several bones contributing to the shoulder or to the pelvis (ranging from completely separate through partially united to fully fused, without even a trace of the suture) that were originally believed to distinguish the various species, are now recognized as natural changes that occurred as individuals grew into adults. Bennett's taxonomic "welfare" work has also been felt elsewhere.10 Under his aegis, different forms of Pteranodon, cruelly divorced from one another for more than a century, are now happily reunited— tall-crested males with short-crested females, in the single species Pteranodon longiceps.

Establishing how different species of pterosaur were related to one another was for many years primarily based on their overall degree of similarity and their geological age. Because the Early Jurassic prow-jawed pterosaur Dorygnathus appeared to be quite similar to the Late Jurassic prow-jawed Rhamphorhynchus, it was not only assumed that they were more closely related to each other than to any other pterosaur, but that Rhamphorhynchus was directly descended from Dorygnathus.11

Modern phylogenetic systematics (which we first met at the end of the previous chapter) largely ignores geological age and employs a more refined technique, whereby rather than utilizing any and every characteristic, be it skull shape, the length of the neck or a detail of the foot, only characteristics unique to particular groups are used to establish genealogy. Moreover, in what was for some researchers a painful break from tradition, species, or the larger groups into which they clustered, were not generally considered to be descended from one another, as you can see in the family tree that appears later in this chapter.

Pterosaurs have recently been subjected to several "phylogenetic analy-ses"12 among the results of which is the discovery that while Dorygnathus and Rhamphorhynchus still belong in the same prow-jawed clan— the rham-phorhynchines—they have been joined by two or three relatives and are no longer thought to be directly related to one another. More importantly for pterosaurologists, the main conclusions of these new phylogenetic studies match well with one another, although discrepancies here and there inevitably continue to fuel debates and squabbles.

That, then, is how pterosaurologists built their pterosaur family tree, but before we set off to explore its various branches and meet some of the inhabitants, an even more general question must be addressed. How are pterosaurs related to other backboned animals? The pterosaur tree is, itself, just a single branch among the many on the great tree of life— but where is that branch upon which pterosaurs sit?

Bird or Bat? Pterosaurs belonged to a large group of vertebrates called the tetrapods— four-footed beasts (Figure 4-3)- That they were amniotes,13 a particular group of tetrapods whose members laid eggs with a waterproof membrane, is shown by several tell-tale features of the skeleton, such as a single rounded knob ofbone on the back of the skull (the occipital condyle), which connects it with the spinal column. Although their amniote credentials have never been doubted, the recent discovery of several fossilized pterosaur embryos "in ovum" in Lower Cretaceous rocks of China and Argentina demonstrates beyond any question that they could produce the ultimate proof of membership of the amniote club: a desiccation-proof egg.14

So far, so good, but now it gets more complicated. In the past, pterosaurs were allied, on different occasions, with each of the three main amniote groups: reptiles, birds and mammals. Pterosaurs certainly belonged within one of these, but which?

One of the biggest blunders to be made by a pterosaurologist was perpetrated by Samuel Thomas von Soemmering, professor of anatomy and surgery at the University of Munich in the early 1800s. Soemmering mistakenly decided that one of the first pterosaurs to be found, a young Ptero-dactylus from the Solnhofen Limestone, was some kind of bat15 and thereby landed pterosaurs among the mammals. Compounding the problem, this error was enthusiastically embraced in some quarters, the English zoologist Edward Newman even going so far as to depict pterosaurs as marsupial bats,16 adorned with fur and sporting a pair of large and rather cute-looking ears. Soemmering was quite wrong, however, as his French contemporary, Baron Georges Cuvier, the father of comparative anatomy, showed in the pages of his 10-volume magnum opus Recherches sur les Ossemens Fossiles.17 Cuvier pointed out numerous features that disqualified pterosaurs from any possible kinship with mammals, including their simple, single-crowned teeth, quite unlike our multi-cusped molars, and the presence of a distinctive "quadrate" bone in the skull, upon which the lower jaw hinged, which is typical of reptiles, but reduced in modern mammals to a tiny element in the ear.18

Another serious misunderstanding of pterosaurs, with ramifications that are still being felt today, was made by Harry Govier Seeley,19 the author of Dragons of the Air. At an early stage in his career, Seeley became quite convinced that pterosaurs were the ancestors of birds, an idea that, according to the English naturalist Richard Lydekker in his review of Dragons, had impressed itself with "peculiar force" upon Seeley's mind.20 Later, as this notion drew increasingly sharp criticism, he shifted, albeit reluctantly, to a slightly

FIGURE 4*3 Where do pterosaurs come from? The upper diagram shows the general relationships of backboned animals and the location of pterosaurs within the reptile group Diapsida. The lower diagram shows the four possible points at which pterosaurs may have arisen from within the diapsids. An origin somewhere within the split between archosauriforms and prolacertiforms seems most likely at present.

FIGURE 4*3 Where do pterosaurs come from? The upper diagram shows the general relationships of backboned animals and the location of pterosaurs within the reptile group Diapsida. The lower diagram shows the four possible points at which pterosaurs may have arisen from within the diapsids. An origin somewhere within the split between archosauriforms and prolacertiforms seems most likely at present.

different position, in which birds shared a common origin with pterosaurs, rather than being directly descended from them. One of the stratagems that Seeley used to bolster his arguments was to make reference to birds in the many new names that he coined for pterosaurs. Thus, we have Omithochei-rus ("bird hand"), Ornithostoma ("bird mouth"), and Ornithodesmus ("bird link")21— and the crowning glory, "Ornithosauria," which he proposed as a replacement for Pterosauria. Despite his inventiveness, Seeley's big idea ultimately failed. His contemporaries, who included such illustrious scientists as Richard Owen, the British version of Cuvier, highlighted the many problems associated with this hypothesis. Pterosaurs, they said, have numerous features in the construction of the skull and design of the hands and feet that resemble the condition in reptiles, but are completely different from those of birds, ruling them out from any close relationship to these feathered fliers.

Reptiles Then, But Which? Cuvier was the first scientist to recognize pterosaurs for what they were— flying reptiles— but it wasn't until the beginning of the 20th century that their reptilian affinities were universally agreed upon. The general relationships of pterosaurs to other reptiles were also established at about this time. The presence just behind the eye of two openings, one above the other, shows beyond any doubt that pterosaurs were diapsids,22 one of the most diverse and prominent of all the amniote groups.

The diapsid line first appeared more than 300 million years ago and subsequently sprouted many important branches, which, apart from pterosaurs, also culminated in lizards, snakes, ichthyosaurs, plesiosaurs, crocodiles, dinosaurs and birds.23 The relationships of these different kinds of diapsids to one another are now fairly well understood, with one glaring exception: pterosaurs. As Figure 4-3 illustrates, paleontologists don't really know where this group should sit within the diapsid family tree.

The reason for this confusion is simple— a complete lack of protoptero-saurs that might link this group to other diapsids. Birds, by contrast, have an almost perfect intermediate— Archaeopteryx— that, with its mosaic of avian and reptilian characteristics, unites them in a most convincing fashion with their reptilian relatives, theropod dinosaurs such as Velociraptor. Pterosaurs have no equivalent of Archaeopteryx and so, at present, sit in splendid isolation, definitely related to, but somehow remote from, other diapsids. Even the earliest, most basic pterosaurs, such as Dimorphodon, which we will meet again later, are pterosaurian through and through, and little of what's known of their anatomy seems to have been left untouched by adaptations for flight, which seem to have had a profound and almost universal impact on their anatomy. This means that many of the features used by paleontologists to reconstruct the genealogy of diapsids, among them skull shape, ankle construction and numbers of fingers and toes, are so altered in pterosaurs that any messages they may contain regarding the origins of these animals are difficult to decipher.

Undaunted by this obstacle, specialists have come up with several different suggestions as to where pterosaurs might be lodged in the diapsid tree. The three main proposals, shown in Figure 4-3? are: perched next to the dinosaurs; squatting among dinosaur's relatives, the archosauriforms; or hanging out with another group altogether, the prolacertiforms.

Dinosaurian Bedfellows? The most popular current notion regarding pterosaur origins is that they were close relatives of dinosaurs. Several features, mostly to be found in the legs of pterosaurs, dinosaurs, birds and a few other reptiles, such as Scleromochlus (Figure 4 - 4 ) ? seem to support this idea and supposedly define a clan that has been named Ornithodira, which means literally "bird-like ankles." With the exception of sauropods and some other dinosaur groups that returned to all fours, perhaps because of their extremely large size, the hallmark of this clan was the ability of its members to move around on their back legs alone, skipping along on the tips of their toes as living ornithodirans— which we call birds— do today. This arrangement— which is quite different from that found in reptiles, where the legs sprawl out sideways as, for example, in lizards and crocodiles— required numerous modifications, such as an in-turning of the head of the thigh bone that allows the legs to be tucked in beneath the body, a relatively long shin and a simplification of the ankle joint— features that are, to some extent, found in pterosaurs.

Scleromochlus, a small reptile from Upper Triassic rocks of Scotland,24 is especially important, because some scientists have suggested that it is the closest known relative of pterosaurs and could even be considered a ptero-saurian Archaeopteryx.25 But there are difficulties with this suggestion and with the more general idea that pterosaurs are ornithodirans. Significantly, the broad, shield-like pelvis of pterosaurs is quite different from that of dinosaurs or Scleromochlus, where it is constructed from bony spars that radiate forward and backward. Moreover, the design of the pterosaur foot, not

FIGURE 4.4 Meet the relatives? All these diapsids— Scleromochlus, an ornithodiran about 8 inches (20 centimeters) long (above); Euparkerui, an archosauriform (middle) about 20 inches (50 centimeters) long; and the 10 inch (25 centimeter) long Sharovipteryx, a prolacertiform (below)— have been proposed as close relatives of pterosaurs.

to mention thousands of tracks (see Chapter 9), show that pterosaurs did not walk or run on their toes, but stamped along in a decidedly flat-footed fashion. So, what about the ornithodiran aspects of pterosaur legs? Nothing to do with ornithodirans at all, some have argued, just features that look superficially similar to those of Scleromochlus and its relatives, but that evolved for a quite different reason— for use in the flight apparatus.26

Further Down the Diapsid Tree? A second possibility is that pterosaurs branched off somewhat lower in the diapsid tree, from among several early lineages of an important diapsid group— the archosauriforms. As Figure 4-3 shows, after lizards and snakes and several other groups, such as the sea-living ichthyosaurs and plesiosaurs, had separated off to follow their own evolutionary destiny, the main diapsid stem split into two major lines. They evolved in one case into prolacertiforms, which we shall return to shortly, and in the other into archosauriforms, a lineage of land-living carnivores that eventually gave rise to crocodiles, dinosaurs and birds.

Traditionally, pterosaurs were thought to have originated from somewhere near the base of the latter group, perhaps not far from Euparkeria, a medium-size, rather generalized archosauriform.27 An in-depth study by Chris Bennett in the mid-1990s arrived at this conclusion and is supported by some archosauriform features found in pterosaurs, such as the presence of an antorbital fenestra— a bone-bounded window that pierced the skull between the openings for the nostril and the eye.

Again, however, there are difficulties with this idea, not least because if it is true, then, as Figure 4 -4 shows, pterosaurs' nearest known relatives were rather large, heavily built, superficially crocodile-like animals with short arms. Other features also speak against this relationship. Another opening, this time in the lower jaw and called the mandibular fenestra, is a particularly telling example. Most archosauriforms have this opening, but pterosaurs do not. This is surprising, because if pterosaurs are archosauriforms, their ancestors must have possessed this opening only for it to have been refilled with bone just as they were evolving into pterosaurs, even though at this point in their evolutionary history, they were also developing a flight ability and, judging by what's known of their skeletal design, losing weight wherever possible.

On Sharov's Wing? A third option is that pterosaurs originated from within another quite different diapsid clan: the prolacertiforms. These generally small, rather lizard-like reptiles28 evolved along several different lines, one of which culminated in Tanystropheus, a bizarre-looking animal that had an incredibly long neck that looks well-suited for cleaning out drains, but is more likely to have been used as a means for reaching its fishy prey.29 One of Tanystropheus relatives, Sharovipteryx, a small, very lightly built, long-legged reptile from the Upper Triassic of Kirghizia,50 illustrated in Figures 4.1 and 4.4, is of special interest because in some respects it really does fit the bill as a pterosaurian ancestor— not least because it seems that it could fly.

Pterosaurs and Sharovipteryx share several unusual features, such as hollow bones and a shin that was longer than the thigh. More importantly, however, Sharovipteryx has superbly preserved impressions of flight membranes that evidently attached to the back of each leg and ran out along the fifth toe— exactly as in pterosaurs. As if that were not enough, details of the wings of Sharovipteryx, shown in Figure 4-4, reveal a very distinctive pattern— numerous, closely packed fine lines running out toward the edges of the membranes. Among all backboned animals, this kind of lineation has only been found in pterosaurs, where, as detailed in Chapter 8, it appears as the external manifestation of an internal structure— long, thin fibers that helped stiffen the flight membranes.

Is this it, then? Is Sharovipteryx the pterosaurian Archaeopteryx? Well, probably not. The difficulty with Sharovipteryx is that while it does share some features in common with pterosaurs, it also has many characteristics that are quite unlike anything found in these animals. There is no antorbital opening between the nostril and the eye, the neck is extraordinarily long, unlike the short neck of early pterosaurs and, according to the latest studies of Sharov-ipteryx, the arms are very short and small,31 exactly the opposite of the condition in pterosaurs. This Middle Asian Triassic aeronaut appears to be more closely related to other prolacertiforms than to pterosaurs, leading to the conclusion that the features of the skeleton and wings that they share in common must have evolved independently in response to the stringent demands of flight. Indeed, pterosaurs lack almost all the anatomical hallmarks of prola-certiforms and probably do not belong within this group at all.32

Outcasts? Pterosaurs certainly belong somewhere in the diapsid family tree, yet, at present, they do not sit comfortably in any of the positions on offer. "Does it really matter?" one might ask. The answer is, "yes, it does." If we had some idea of how pterosaurs were related to other diapsids, we could at least begin to understand what their ancestors looked like, how they evolved their most characteristic feature— wings— and under what circumstances this might have taken place.

We will return to this issue at the start of the "Pterosaur Story" (see Chapter 10), but for now, the best accommodation for these outcasts is a temporary dwelling in a cleft in the tree between the archosauriforms and the prolacertiforms (see Figure 4.3). It is not ideal, but it is the least uncomfortable fit for all the anatomical features that we have met so far. At this location, one would expect to find diapsids with an antorbital opening but no mandibular fenestra, along with hollow limb bones, a long shin, and a simplified ankle construction. All these particulars are, at least, found in pterosaurs, but I should point out that they form just a tiny part of the large and still expanding mass of data being used by paleontologists to map out the relationships of diapsids. Where pterosaurs will finally come to roost in this family tree is still quite unclear.

Pterosaur, or Not Pterosaur? Before we get to grips with the pterosaur family tree, we must briefly consider another important issue: How do we decide who actually belongs in the clan Pterosauria, to give it its formal name, and who does not? Happily, on this occasion, pterosaurs' highly distinctive anatomy and the large gap between them and other diapsids is very helpful. It means that usually it is quite easy to determine whether a fossil is pterosaurian.

Among the characteristics that proclaim a fossil to be pterosaurian, one of the most useful is the remarkable thinness of their bone walls. Typically, they are only 1 or 2 millimeters thick, even in giant species. This immediately distinguishes pterosaurs from other animals, even those with hollow bones, such as birds and some dinosaurs, where the walls are almost invariably thicker. Remarkable as it may seem, using this feature, even badly preserved, isolated bones that have been through so much that all their articular ends have broken off and only a piece of shaft remains can still be confidently identified as pterosaurian.

Other unique features, often sufficient to tell at a glance that one is dealing with a pterosaur, include the enormously enlarged fourth finger of the hand— the wing-finger— composed of long, spar-like bones; the highly distinctive design of the wrist, which contains the pteroid, a rod-like element only found in pterosaurs; and the peculiar design of the foot, which, in many species, sports a long, clawless, fifth toe quite unlike anything found in other reptiles, living or extinct.

Despite these and numerous other distinctive skeletal details, discussed more fully in the next two chapters, pterosaurs have sometimes been mistaken for other animals, usually birds33— or other animals, usually birds, have been mistaken for pterosaurs. The most notorious example concerns a character we have met before, Richard Owen, one of his bitterest rivals, Gideon Mantell,34 and several small, delicate bones purchased by Mantell in the early 1800s from quarrymen working the Lower Cretaceous rocks of Tilgate Forest in Sussex, England. Mantell, a doctor from Lewes who became famous for making some of the earliest discoveries of dinosaurs, was sure that these bones belonged to birds, an idea that was supported by Georges Cuvier and, initially, by Owen. Later, however, Owen changed his mind and, without telling anyone, prepared a scientific paper that he sprung on his contemporaries, including an outraged Mantell, in which he opined that all the "Wealden 'birds' are pterodactylian."35 Relations between these two scientists reached a new low, with Mantell confiding to his diary, "It is deeply to be deplored that this eminent and highly gifted man, can never act with candor or liberality."36 But, as is often the case, Owen was right, and Mantell's birds proved to be pterosaurs after all.37

A reverse example, wherein a supposed pterosaur proved to be something else, fell to my own experience in the early 1990s. During a visit to Beijing, I was asked to inspect a small, headless, rather jumbled-up skeleton about the size of that of a thrush, which had been collected from Lower Cretaceous rocks in Inner Mongolia, China. Although identified as a pterosaur, it just did not seem to have enough wing-finger bones, a problem that disappeared when I came to the realization that it was a bird and not a pterosaur at all.38 To my chagrin, this new identity seemed to spark much more interest in the fossil than had been the case when it was still a mere pterosaur.

Up the Tree The general layout of the pterosaur family tree, illustrated in Figure 4-5, has eight main branches. The arrangement of these branches and the species that belong to them, listed at the end of this book, are generally agreed upon by pterosaurologists, although, inevitably, disputes about some of the fine details remain. The lowermost four branches, consisting almost entirely of long-tailed pterosaurs, are traditionally grouped together as the rhamphorhynchoids, a name derived from one of the best-known members of this group— Rhamphorhynchus. The uppermost four main branches, forming the crown of the tree, are referred to collectively as the pterodactyloids, short-tailed pterosaurs whose common ancestry is signposted by a row of unique features, not least, their relatively short tails.

FIGURE 4*5 The pterosaur family tree, showing the main branches and some of the principal players. Clockwise, from left, with size given in centimeters (cm): Dimorphodon (22cm) Eudimorpbodon (9cm), Campyognathoides (13cm), Istiodactylus (about 56cm), Ornithocheirus (67cm), Pteranodon (100cm), Germanodactylus (13cm), Dsungaripterus (41cm), Tapejara (20cm), Tupuxuara (85cm), Zhejiangopterus

(29cm), Ctenochasma (10cm), Gnatbosaurus (28cm), Pterodactylus (9cm), Rhamphorhynchus (10cm), Seaphognathus (12cm), Anurognathus (3.2cm). Branch names are as follows: 1, Dimorphodontidae; 2, Anurognathidae: 3, Campylognathoididae; 4, Rhamphorhynchidae; 5, Pterodacryloidea; 6, Ornirhocheiroidea; 7, Ctenochasmatoidea; 8, Dsungaripteroidea; 9, Azhdarchoidea.

FIGURE 4*5 The pterosaur family tree, showing the main branches and some of the principal players. Clockwise, from left, with size given in centimeters (cm): Dimorphodon (22cm) Eudimorpbodon (9cm), Campyognathoides (13cm), Istiodactylus (about 56cm), Ornithocheirus (67cm), Pteranodon (100cm), Germanodactylus (13cm), Dsungaripterus (41cm), Tapejara (20cm), Tupuxuara (85cm), Zhejiangopterus

(29cm), Ctenochasma (10cm), Gnatbosaurus (28cm), Pterodactylus (9cm), Rhamphorhynchus (10cm), Seaphognathus (12cm), Anurognathus (3.2cm). Branch names are as follows: 1, Dimorphodontidae; 2, Anurognathidae: 3, Campylognathoididae; 4, Rhamphorhynchidae; 5, Pterodacryloidea; 6, Ornirhocheiroidea; 7, Ctenochasmatoidea; 8, Dsungaripteroidea; 9, Azhdarchoidea.

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