Palaeos Vertebrates Pterosauria

large eyes; sizeable brains; hollow long bones; sternum but small or no ossified keel); long retroverted scapula as in birds; ventral edge of coracoid articulates with sternum as in birds and supports pectoral girdle [P97]; expanded sternum with keel [P97]; humerus longer than sternum [P97]; big deltopectoral crest on proximal. humerus for flight stroke muscles [P97]; primitively, deltopectoral crest has straight edges [P&S]; forearm longer than humerus [P97]; pteroid bone in wrist; hand with elongate digit 4 supporting wing membrane; manus 1-3 retained, with unguals, and at least sometimes robust [U99]; wing membranes with fibers for stiffening [P97] (contra [U99] who suggests that wings were supported largely by physical attachment to legs, cranium, etc.); short pubis with pre-pubic bones; highly mobile hip joint [U99]; femur bowed and shorter than tibia [P97]; fibula reduced and fused to tibia [P97]; mesotarsal ankle [P97]; 4 elongated, closely appressed metatarsals plus reduced 5th [P97] (contra, Bennett (1997), who states that the metatarsals were flexible: closely appressed in flight, but spread in walking); pes with 5 digits; pes 5 small & without claws [U99]; longish penultimate phalanges on feet (not digitigrade?) [U99]; wing membrane extends to leg in some or all groups, even between rear legs (uropatagium); pteroid supports additional membrane to neck; fibers in membrane; typical gait may have been quadrupedal and plantigrade, with limbs at least partly sprawling [U99]; bones generally highly pnematic or hollow & supported by internal struts [P97]; integument possibly with hair-like pilosity [P97] (widely disputed).

Image: comparison of bird, bat & pterosaur pectoral girdles from Padian (1997a).

Note: Padian (1997a) identifies several features as synapomorphies, but then states that most are shared with dinosauromorphs. 011010.

Range: Late Triassic (Norian) to Early Jurassic (Sinemurian) of Europe for Dimorphodon. Inclusion of Sordes extends range to Asia and the Late Jurassic. Various unconfirmed bits and pieces suggest a worldwide distribution.

Introduction: Dimorphodon macronyx, from the Lower Lias of Lyme Regis, Dorset, and Aust Cliff, Gloucestershire is the only certain member of the family Dimorphodontidae. Only a few specimens are known; all but one (the one illustrated) coming from the Sinemurian of the Dorset Coast of England.
This primitive pterosaur had quite a large, deep skull that was also very lightly built, consisting of large openings separated by narrow strips of bone. The tail was long, with the first five or six vertebrae short and flexible, and the rest elongated and stiffened against each other by long strips of bone. The tail was thus a long stiff rudder, flexible only at the base, and used for stabilization in flight. The overall length was up to 100 cm, with a wingspan up to 1.4 metres. The hind legs were long and powerful, indicating that Dimorphodon was able to walk competently on land, bird or dinosaur fashion. (MAK 991008)

Characters: medium-sized; large, deep skull; maxilla does not extend posteriorly to the level of the orbit; nasal breaks contact between ascending process of maxilla and lacrimal; cranial struts very thin; cervical ribs tiny; tail long; first five or six caudal vertebrae short and flexible, and the rest elongated and stiffened against each other by long strips of bone (tail used as rudder, flexible only at base); sternal complex wider (laterally) than deep; deltopectoral crest with bulbous distal expansion [P&S]; metacarpals roughly equal in length; large wing claws; legs long; metatarsals tightly appressed; brachiopatagium attached to ankles and uropatagium even to toes in Sordes [U99].

Notes: [1] the name is derived from the dimorphic teeth: large conical stabbing teeth anteriorly, and tiny pointed teeth posteriorly. However, many types of pterosaur developed similar specializations and this particular trait may be characteristic of the pterosaurs as a whole. [2] Sordes is variously classified as just basal to this group, as a dimorphodontid, or as a rhamphorhynchoid (U&B). Nesodactylus is known from a rather incomplete specimen from the Late Jurassic of Cuba. [3] Sordes has also been at the heart of the controversy relating to wing attachment, with Unwin and others using some of these beautifully preserved specimens to show that the wing was attached far down the ankle, as well as extending between the legs, making bipedal locomotion almost impossible.

Image: This specimen, from the Late Jurassic of Kazakhstan, is one of the Sordes specimens which caused all the ruckus about pterosaur "hair." The current thinking is that these are elastic fibers from inside the wing membranes, and not integumentary hair. The image is said to be © Prismatic Productions. However I am very dubious of this claim. Further, the links to this entity and the alleged authors are not functional. So sue me.

Campylognathoidea: Campylognathoides, Eudimorphodon (Eur, India, Greenland?)

Characters: medium to large (wingspan 1-6 m); long jaws, slightly curved anteriorly; numerous sharp teeth; relatively short neck; long tail with terminal diamond-shaped flap.

Rhamphorhynchoidea: Rhamphorhynchus, Scaphognathus. Definition: Rhamphorhynchus > Pterodactylus.

$ skull more than three times longer than deep (U&B); bony mandibular symphysis; $ very large, protruding anterior teeth; $ mandibular teeth not dimorphic (?!) (U&B); $ tip of lower jaw (predentary?) dorsally deflected, toothless and very sharp; $ premaxillae separate frontals (U&B); $ orbits larger than nasal and preorbital openings (U&B); $ prepubes ventrally oriented; long, stiffened tail, sometimes with "rudder"; deltopectoral crest with bulbous distal expansion [P&S]; 5-6 carpals; $ metatarsal 4 reduced in length (U&B); loosely appressed metatarsals; pes 5 retains 2 phalanges & is hooked or retroverse. Tail probably provided stability, but less maneuverability.

Image: Rhamphorhynchus, from the Brooke Bond tea cards -- traditional, but many are very well done.

Notes: Many sources use the traditional notion of Rhamphorhynchoidea as including almost all Jurassic pterosaurs.

Introduction: advanced forms from the Late Jurassic and Cretaceous. Small to very large. Short tails. The neck is longer (although with the same number of vertebrae) and the brain is larger. In some forms a head crest developed to aid in manoeuvourability during flight. The teeth are reduced and sometimes absent.

Characters: all relatively large as adults [B96]; skull elongate & laterally compressed [K&L]; cranial bones usually fused in adults; $ jaws triangular with tendency to lose teeth [P97]; premaxilla usually forms anterodorsal portion of skull, including at least part of rostrum [K&L]; maxilla lies below premaxilla and forms sides of upper jaw and anteroventral margin of nasoantorbital fenestra; $ nares absent or confluent with antorbital fenestra [K&L][P97]; cranial crests [B96]; articular condyles of quadrate helical in some large forms [K&L]; anterior trunk vertebrae fused into notarium; tail reduced or absent maneuverability); scapula curved inward and articulated with notarium (stronger flight stroke) in larger species [P&S]; glenoid directed posterolaterally rather than laterally) since scapulocoracoids now formed parts of a ring structure with sternum and notarium; metatarsals flexible --appressed for flying & spreadout for walking [B97]; outer layer of bones 1-2 mm in large forms, supported by internal struts [K97]; integument very thin, probably without scales or "hairs" [K97]; at least small forms probably quadrupedal, using manus digits 1-3 spread laterally or retrograde [B97].

Discussion: In the brief period between about 1980 and 2000, dinosaurs evolved from long-extinct, slumbering mountains of swamp-dwelling flesh -- barely swifter than continental drift -- to hot-blooded athletes who dominate the skies even today. We will pointedly ignore the question of whether this reinvention of the taxon has gone just a shade too far. The astounding success of the general reinterpretation can legitimately cause us to wonder whether even the most outlandish claims for the abilities, metabolism, prowess and intelligence of the dinosaurs might not turn out to be well founded after all. But every success breeds imitators, and not every imitation matches the quality of the original. The pterosaurs, who underwent a parallel transformation in the scientific literature, now seem to be devolving back into a more traditional mold.

For a while, in the early 1990's, it seemed that pterosaurs were almost more birdlike than birds. They were characterized as active, deep-keeled, flapping flyers in the air and as lithe bipedal runners on land. They were covered with hair and distinctly warm-blooded. Their wings were narrow and held in place by keratinous rods of some unique and advanced design. They were loving parents who engaged in extended care of their chicks [1]. They finished the Times crossword before their second cup of coffee went cold. The name of Kevin Padian [2] is frequently invoked for this interpretation, although it would be unfair to ascribe the more extreme expressions of these views to Prof. Padian.

It all seemed a little too good to be true -- and it probably was. One stumbling block is Pteraichnus, probable pterosaur footprints from Arizona and Wyoming. Similar prints have been found in France. Actually, the track maker was not stumbling, but it was certainly not a biped. Nor does it appear to have been an ordinary quadruped. Images of these tracks are found at right (from Bennett 1997)) and under the main heading for this taxon. Padian showed that similar tracks could be generated by crocodilians, specifically by Caiman, under appropriate experimental conditions. However, the appropriateness of these conditions has been criticized, as has the similarity of the prints. See, e.g., Bennett (1997) and Unwin (1999). It has been reported that Padian has also recently stated that certain similar trace fossils are probably pterosaurian.

If this is correct, then pterosaurs were not only quadrupeds, but probably somewhat sprawling quadrupeds who walked a bit awkwardly on plantigrade feet and almost retrograde fingers. Perhaps this proves too much, since it is hard to see how a really large pterodactyloid could have moved in this manner. But, then again, it is hard to see how something like Quetzalcoatlus could have moved in any manner on the ground. It is probably safe to say that pterosaurs were not cursorial bipeds, but distinctly hazardous to say much more than that.

Another difficulty has been the beautifully preserved remains of Sordes from Sölnhofen and of more exotic species from the Brazilian Santana Formation. The pterosaur "hair" is probably internal membrane fibers, the main wing membrane (brachiopatagium) was fastened well down the leg, and a distinct cruropatagium joined the legs, held in place by the retroverted fifth toe. If pterosaurs ran, they did so in heavy floor-length gowns. As any reasonably articulate feminist will be happy to explain, the whole point of such attire is to make it more difficult either (a) to get anywhere or (b) to accomplish any useful work. I hasten to disclaim any opinion on the politics and intent, if any, of gender-specific fashion statements -- although it is interesting that traditional academic garb is designed along the same lines -- but one is forced to concede the practical consequences. A fully accoutered pterodactyloid might manage a stately pavan, but was clearly not designed for the ptango.

Unwin goes so far as to suggest that this deconstruction of the pterosaurs might require us to place pterosaurs back among the basal archosauromorphs or even in the basal diapsids, a theory that was worked out in some detail by Peters in the sadly missed Pterosaur Home Page and various JVP abstracts. Unfortunately almost all pterosaur phylogenetic work is published in the form of JVP abstracts, so it is difficult to comment. Unwin cites work by Bennett for the idea that only characters of the hind limb place pterosauria among ornithodires. However, this is a little unfair since Ornithodira, as well as the clades it contains, largely reflect key transitions in hind limb locomotion. The growth of this whole branch of the Tree seems to have been driven by hind limb design. See, e.g., Hutchinson & Gatesy (2000), Novas (1996), and review by White 2001). Thus, it may be meaningless to speak of ornithodires without ornithodire hind limbs. It is only a slight exaggeration to say that ornithodires are all archosauromorphs with the specialized ornithodire hind limb. However, it may be possible that the ornithodires are cursorial descendants of little gliding or even flying archosaurs, and that the pterosaurs were an early radiation of that line. This is sheer speculation, of course, but it has the advantage of accommodating all schools of thought and even providing a little vindication to the much reviled work of John Ruben. See, e.g., Jones et al. (2000).

[2] In the interests of full disclosure, I should state that I hold, and have strongly expressed, negative opinions about Dr. Padian's statements on certain subjects. These subjects are not among those discussed anywhere in Palaeos, but the reader is duly warned of a potential bias. (ATW 011012.)

Characters: $ mandibular symphysis large, bearing substantial teeth (U&B); $ symphysial teeth include 3 pairs of large, fang-like teeth (U&B); $ symphysis with marked midline channel bounded by ridges (U&B); median palatal longitudinal ridge [K&L]; $ saggital crests near ends of jaw (U&B); deltopectoral crest "warped" , i.e. not at right angles to shaft of humerus [P&S].

Dsungaripteroidea: Domeykodactylus, Dsungaripterus, Noripterus, "Phobetor"

Azhdarchoidea: Arambourgiania, Azhdarcho, Doratorhynchus, Montanazdarcho, Quetzalcoatlus, Titanopteryx.

Characters: cranial crests small or absent; mid-cervical vertebrae highly elongate (U&B); large humeral head; tall, squarish deltopectoral crest on humerus, at right angles to humeral shaft and with outer distal) edge concave [P&S]; deltopectoral crest lacks bulbous distal expansion; $ 2nd wing phalanx has T-shaped cross-section due to pronounced ventral keel (U&B); outer layer of bones, esp. of largest forms, only 2mm thick.

Notes: Quetzalcoatlus is generally believed to be the largest flying vertebrate, as well as one of the last pterosaurs. 011007

Pterosauria

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