Pterosaur

I

Introduction

Pterosaur flying reptile that existed during the Mesozoic era from the late Triassic Period to the end of the Cretaceous Period. Fossil remains of pterosaurs have been found in all continents, as well as on the islands of Greenland, New Zealand, and Cuba. Some pterosaurs grew to gigantic size and were the largest flying creatures ever. Paleontologists (scientists who study fossils) usually classify pterosaurs as archosaurs, a group of animals that also includes crocodiles and dinosaurs. The word pterosaur comes from the Greek words pteron (meaning “wing”) and sauros (meaning “lizard”). Pterosaurs are often popularly referred to as pterodactyls.

II

Characteristics of Pterosaurs

Pterosaurs did not have feathers, but a number of well-preserved fossils show that they had a furlike covering on parts of their bodies. Their wings were membranes of skin that extended along the sides of the body, and were attached to the extraordinarily long fourth digit of each arm. The bones were hollow and had openings at each end. Unlike typical reptiles, pterosaurs had a breastbone that was well developed for the attachment of flight muscles. Pterosaurs also had more advanced brains and senses, with good vision, balance, and coordination. These features suggest to some scientists that pterosaurs were active and agile animals that were to some degree warm-blooded, similar to birds and mammals.

Scientists have found intriguing clues to pterosaur behavior. Some types of pterosaurs had strange crests on their heads. The crests were made of bone or of horny tissue, and were likely used to indicate sexually mature adults of different sexes. Hundreds of fossil nests found together indicate some species gathered in colonies to reproduce. Embryos discovered inside eggs suggest that some pterosaurs could probably fly after they hatched, and may not have needed to be fed by parents. Studies of many specimens of the same species at different ages indicate that some pterosaurs grew in rapid spurts and began to reproduce before they reached full adult size, which took a number of years. This pattern has also been found in some dinosaurs, and differs from birds, which do not reproduce until fully grown.

The shapes of pterosaur jaws and teeth indicate they had different diets. Some ate mainly fish, while others ate insects or shellfish. Some had thin comblike teeth to strain water for small invertebrates. A few large forms may have preyed on small reptiles and other land animals. Fossil trackways show that pterosaurs walked on all fours with their wings folded back. Large, sharp claws on their fingers and toes suggest some could also climb up rocks or trees. Their feet were webbed and may have allowed them to paddle in water. How pterosaurs got airborne is still debated. Some pterosaurs were active flappers, but other larger types likely soared on the wind like modern albatrosses.

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III

Evolution of Pterosaurs

Although paleontologists have found fossils of different types of gliding reptiles that lived before the first pterosaurs appeared, none of these animals have the special kind of wing and other features that evolved in pterosaurs. The direct ancestors of pterosaurs are still not known, but they were probably small archosaurs closely related to the ancestors of dinosaurs. Pterosaurs appeared during the late Triassic Period and were the first known vertebrates (animals with backbones) to actively fly, not just glide. However, pterosaurs were not the ancestors of birds. Birds evolved from small meat-eating dinosaurs about 60 million years after pterosaurs appeared and have wings formed with feathers, not stretched skin.

In early pterosaurs of the late Triassic Period, the skull was about 9 cm (about 3.5 in) long and the body was about 10 cm (about 4 in) long. The flexible tail, which was about 38 cm (about 15 in) long, had a diamond-shaped terminal appendage, used as a rudder in controlling flight. Later pterosaurs had short tails. Pteranodon from the Upper Cretaceous Period had a wingspread of more than 6 m (more than 20 ft). Its skull was long and slender, and the jaws were toothless.

Early in 1975 scientists announced that partial skeletons of three huge, long-necked pterosaurs had been discovered in the Late Cretaceous non-marine rock at Big Bend National Park in Texas. With an estimated wingspan of about 11-12 m (about 36-39 ft), the Big Bend pterosaur became the largest flying creature known to have existed. Scientists named it Quetzalcoatlus, after the Aztec god Quetzalcoatl. Fossils found in Spain and Romania indicate that other types of pterosaurs grew to similar gigantic size.

Scientific classification: Pterosaurs make up the order Pterosauria. A well-known genus of the pterosaurs of the late Jurassic Period is Rhamphorhynchus. A well-known genus of the later pterosaurs of the Upper Cretaceous Period is Pteranodon.

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