Pterodactyloids

The first fossils of short-tailed Pterodactyloidea were discovered in the Upper Jurassic strata of Europe. They were assigned to the genus Pterodactylus (Fig. 55; 'flight finger'), and possessed all the typical features of pterosaurs. Many different species of Pterodactylus have been found, varying mainly in size and the shape of the head. Their narrow jaws and sharp teeth suggest that they must have been mainly piscivorous, like most of the rhamphorhynchoids.

Nothing is known about the direct ancestors of the pterodactyloids, but it can be presumed that they were descended from rhamphorhynchoids and evolved during the Early or Middle Jurassic. They were probably more adroit fliers than their ancestral clade which may eventually have lost out in competition with them. Whereas many of the Rhamphorhynchoidea would mainly have flown with their heads and necks extended, as shown in my earlier drawings, most of the pterodactyloids balanced themselves in flight by curling their long necks backwards, as pelicans do (see below). Another advantage of their behaviour has already been discussed in the case of Dimorphodon and Rhamphorhynchus (Sect. 6.5), which used their long necks to lunge forward when they capture prey.

Gallodactylus
■ Fig. 61. Left Germanodactylus (Pterodactyloidea; Upper Jurassic), roosting beneath a branch (wingspan ca. 1.1 m). Right Gallodactylus (Pterodactyloidea; Upper Jurassic; wingspan ca. 1.4 m). (After Wellnhofer 1991)

In addition to more than a dozen species of Pterodactylus, Upper Jurassic Pterodactyloidea included species of Germanodactylus, Gallodactylus, Cteno-chasma, Gnathosaurus, Huanhepterus, Dermodactylus, and Mesadactylus (Wellnhofer 1991). The pterodactyloids radiated even more extensively during the Cretaceous (see below).

Germanodactylus and Gallodactylus were contemporaries in the Upper Jurassic of Europe, although Germanodactylus has also been recorded from older strata; but neither of these genera survived into the Cretaceous period. The typical characteristics of Germanodactylus spp. (Fig. 61) were low crests of bone along the centre of the skull, beginning above the nostrils and extending over the eye sockets. Germanodactylus spp. had long rows of short and powerful teeth. In G. cristatus, the tips of the jaws were toothless (Fig. 62a). They were probably covered by pointed, horny beaks. Gallodactylus (Fig. 62b), on the other hand, had an elongated jaw with only a few slender teeth at the front of the beak. These pointed forwards and would have grasped slippery fishes most effectively.

Ctenochasma is a rare European genus from the Solnhofen limestone of Bavaria. Its long, slender jaws (Fig. 62a) contained over 250 teeth in the adults. They formed a strainer with which items of food must have been filtered from the sea. Presumably these pterosaurs either swam, or waded in shallow water as

■ Fig. 62a-f. Heads of Jurassic pterodactyloid pterosaurs (not to scale). a Germanodactylus (Upper Jurassic), b Gallodactylus (Upper Jurassic), c Ctenochasma (Upper Jurassic), d Gnathosaurus (Upper Jurassic), e Dsungaripterus (Upper Jurassic and Lower Cretaceous), f Phobereptor (Upper Jurassic and Lower Cretaceous. (Mostly after Wellnhofer 1991)

■ Fig. 62a-f. Heads of Jurassic pterodactyloid pterosaurs (not to scale). a Germanodactylus (Upper Jurassic), b Gallodactylus (Upper Jurassic), c Ctenochasma (Upper Jurassic), d Gnathosaurus (Upper Jurassic), e Dsungaripterus (Upper Jurassic and Lower Cretaceous), f Phobereptor (Upper Jurassic and Lower Cretaceous. (Mostly after Wellnhofer 1991)

many shore birds do today. Gnathosaurus, also from the Solnhofen limestone, is likewise extremely uncommon in the fossil record. It, too, has long and slender jaws (Fig. 62d), but there were only about 130 teeth for filtering food. However, Ctenochasma was a rather small pterosaur while Gnathosaurus had a wingspan of ca.1.7 m and would have strained much larger food items through its teeth.

Dsungaripterus (Fig. 62e) and Phobereptor (Fig. 62f) both arose in the Upper Jurassic and extended into the Cretaceous. Fossils of the former genus have been found in the Upper Jurassic of Africa and the Lower Cretaceous of China. A moderately large pterodactyloid, Dsungaripterus, had bony crests along the midline and back of its skull. Its eye sockets were unusually small, its jaws pointed and curved. They may well have been used as forceps to probe for small aquatic organisms, while the blunt, bony projections further back crushed their shells (Fig. 62e).Although considerably smaller, Phobereptor had similar bony cranial crests. Its jaws were pointed, but straighter than those of Dsungaripterus. Moreover, Phobereptor had true teeth (Fig. 62f). It probably fed in a similar manner to that of Dsungaripterus (to which it was almost certainly related), but on smaller prey.

Cretaceous Pterosaurs

The Cretaceous period began with the separation of the supercontinents Laurasia and Gondwana (Sects. 2.2,3.3) and continental drift continued until the end of the Mesozoic Era and then almost stopped. Dinosaurs dominated the land throughout this time but, although birds became increasingly numerous and conquered various terrestrial habitats (Sect. 8.4),pterodactyloids continued their domination of the air - especially over the oceans. They diversified in the Lower Cretaceous, flourished during the middle of the Cretaceous and finally died out in the Upper Cretaceous. In general, they showed an enor-

Araripedactylus
■ Fig. 63a-i. Heads of Cretaceous pterodactyloid pterosaurs (not to scale). a Ornithocheirus, b Ornithodesmus, c Cearadactulus, d Tropeognathus, e Anhanguera, f Pterodaustro (Lower Cretaceous); g Pterandon ingens, h P. steinbergi, i Quetzalcoatlus (Upper Cretaceous). (Mostly after Wellnhofer 1991)

mous increase in size during this time. Many of the largest forms, such as Azhdarcho, Titanopteryx, Doratorhynchus, Pteranodon, and Quetzalcoatlus had very long and slender necks with elongated vertebrae.

The skulls of several of these genera have been preserved in the fossil record, and reconstructions of the heads of nine of them are illustrated in Fig. 63. Ornithocheirus (Fig. 63a) from the Lower Cretaceous of Europe had long, narrow jaws studded with numerous short, sharp teeth suggesting that it was probably another fish eater. Another rare European Cretaceous pterosaur was Ornithodesmus (Fig. 63b). With a wingspan of ca. 5 m, Ornithodesmus was twice the size of Ornithocheirus (whose wingspan was only ca. 2.5 m). Moreover, it differed from other pterosaurs in that the front ends of its jaws were broad and rounded. This gave them the general appearance of a duck's beak. Unlike that of a duck, however, the front part of the beak of Ornithodesmus was armed with short, strong and alternately meshing teeth suggesting that, once again, this pterosaur was piscivorous. So, too, was the South American Cearadactylus (Fig. 63c) which, with a wingspan of ca. 5.5 m, was even larger than Ornithodesmus. Contemporary with Ornithodesmus was Tropeognathus (Fig. 63d), a large, toothed and crested pterosaur from Brazil (wingspan ca. 6.2 m), Santanadactylus, Araripedactylus, Tapejara, and Anhanguera (Fig. 63e). One of the best-known Early Cretaceous pterosaurs, Anhanguera, had deep bony crests at the front ends of both upper and lower jaws. These may have served as stabilising devices when the pterosaur was skimming the water for fish as,indeed,may have the jaw crests of Tropeognathus (Sect. 6.7.1). The wingspan of Anhanguera was ca. 4 m.

Although Dsungaripterus had bony knobs in place of true teeth, and some genera were toothless (see below), the majority of pterosaurs possessed fairly simple teeth. An exception was the South American Pterodaustro (Fig. 63f). This rare genus had a unique type of dentition. The skull was markedly elongated and the anterior portion curved upwards. The lower jaw was equipped with about 500 bristle-like teeth which could have formed an extremely efficient filtering apparatus. The small organisms filtered from the water were then chopped up by the short, blunt teeth in the upper jaw. The wingspan of Pterodaustro (ca. 1.3 m) was only marginally greater than that of Ctenochasma (Fig. 62c), but its filtering apparatus was adapted to catch very much smaller animals. It was an ecological equivalent of the flamingos, and probably ate both zooplankton and red algae, as flamingos do. Bakker (1987) even suggested that these pterosaurs may have been pink in colour when alive just like flamingos!

Larger predators tend to capture larger prey unless, like whalebone whales, manta rays (Manta birostris), and basking sharks (Rhincodon typus), they are so enormous that they have to be filter-feeders (Sect. 5.5). This, of course, is reflected in their dentition: but other factors are involved too - especially in the case of aerial predators. Large teeth are relatively heavy and tend to upset the balance in the air of those predators that possess them. Birds benefit in having horny beaks which are relatively light in weight: the heavy part of their digestive apparatus, the grit in the gizzard, is sited near the centre of lift between the wings. Flying animals with long necks would be especially affected if they bore heavy teeth in their jaws. It is surprising, therefore, that relatively few pterosaurs evolved horny beaks instead of teeth. Those that did so include Tapejara, Tupuxuara, Nyctosaurus, Pteranodon, and Quetzalcoatlus. The first two were found in the Lower Cretaceous of Brazil, while the remainder date from the Upper Cretaceous. It seems probable, therefore, that toothlessness evolved more than once amongst the pterosaurs, and that the shapes of beaks varied according to their functions, as they do in birds.

Nearly a dozen species of Pteranodon (Fig. 53) have so far been discovered. Among the best known are P. ingens (Fig. 63g) and P.sternbergi (Fig. 63h) from North America. P. ingens had a wingspan of ca. 7 m, while that of P.sternbergi was up to ca. 9 m. These were all toothless fish-eaters like modern sea birds: fishes and crustaceans have been found in the fossils of their throat sacs (Sect. 6.7.1). Their short, smooth fur was probably kept dry by the use of oil, just as the hair of fruit bats (Pteropus spp.) is kept in condition with oil from the neck glands. Moist parts of the body would have been groomed by the legs, which were long and sufficiently flexible to reach almost everywhere, except for the wing claws and the regions adjacent to them, which were within reach of the beak. Their colour was probably dark, as a protection from ultraviolet (UV) light (Bramwell and Whitfield 1974). Finally, the giant Quetzalcoatlus (Fig. 63i) probably used its slender, horny beak to probe for molluscs and crustaceans in shallow flood basins (Langston 1981).Fossils of Quetzalcoatlus have been found in rock that is almost devoid of fish remains. Burrowing animals were, however, present and the pterodactyl probably fed on these. Fossilised logs in the same strata suggest that periodic flooding took place, possibly resulting from a monsoon type of climate.

Wellnhofer (1991) has described many other genera of pterosaurs, often based on quite fragmentary fossil evidence, but superbly illustrated by John Sibbick. Clearly, the pterodactyloids enjoyed worldwide distribution from the beginning of their evolution.

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Responses

  • duenna
    What is the difference between a pterandon and a pterodactyl?
    8 years ago
  • sky
    Which was bigger Ornithocheirus or Quetzalcoatlus?
    8 years ago

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