Animalia Life

Pterosaurs ("winged reptiles") were flying reptiles of the Mesozoic Era, and the first of only three vertebrate groups known to have evolved active flight. Pterosaurs first appear in the paleontological record about 225 million years ago, during the late Triassic Period, and persist to the terminal Cretaceous extinction event, about 65 million years ago.Pterosaurs are recognized as being members of the group Archosauria, a group including thecodonts, crocodiles, birds, and dinosaurs. While pterosaurs were contemporaries to the great Mesozoic dinosaurs, and often confused with them, pterosaurs were not dinosaurs. The origin of pterosaurs is a subject of great debate. Pterosaurs share some physical characteristics in the hips and legs with early dinosaurs. It has also been suggested they could run bipedally and took to the air by the energy-consuming method of running and flapping their wings. Another view suggests pterosaurs pursued a treedwelling way of life, and developed parachuting, gliding, and eventually flight as an energy-saving byproduct of their lifestyle. Another debate surrounds whether pterosaurs were warm-blooded or cold-blooded creatures. Some fossil remains suggest certain pterosaurs may have been covered with short, thin fur, or even very fine feathers. This, combined with the energy-consuming activity of flying, leads many researchers to favor warm-blooded pterosaurs. The first pterosaur fossils were discovered in the Solnhofen Limestone Formation in Germany, in 1784. Pterosaur fossils range in size from those of Pterodactylus, whose forty-centimeter wingspan was about that of a modern song bird, to Quetzalcoatlus, whose fifteen-meter wingspan was as big as a modern private aircraft wing. Pterosaurs had light, bony skeletons made of hollow, tubular bones, and compact bodies to improve wing support. The pelvis and hind limbs were small, yet long and slender when compared to the fore limbs and shoulders. The fore limbs were exaggerated in comparison to the hind limbs, with their great length derived from the extended fourth finger, which alone supported the flight patagium. The pterosaur patagium was a soft membrane thought to have been tougher and thicker than a bat's wing, and divided into three anatomical segments. One short segment stretched from the torso to the elbow end of the humerus; a second, longer segment stretched from the radius and ulna and the bones of the wrist and palm; and the third, longest segment was an elongated fourth finger supporting the wing membrane to its tip. The segments of the wing were progressively longer as they got farther from the trunk. The first, second, and third fingers were not involved in membrane support but were free to grasp and cling; there was no fifth finger. This "finger-wing" configuration is quite different from the wing support structure seen in bats and birds.

Types of Pterosaurs
Pterosaurs are generally divided into two groups: The rhamphorhynchoids first appear during the Triassic, and the pterodactyloids appear some 108 million years later. The Rhamphorhynchoidea had teeth, long tails, short metacarpals, long fifth toes, and a head held in front of and slightly above the torso. The Pterodactyloidea had no tail or fifth toe, an elongated metacarpus forming the largest support structure of its wing, a more "birdlike" neck posture with the neck curving in an S-shape entering the cranium frombelow rather than from behind, holding the head higher above the torso, and many had evolved toothless beaks. Pterodactyloidea, such as Pteranodon, also evolved extreme head crests, and like many later pterosaurs, lacked well- developed teeth. Many other pterosaur fossils exhibit well-developed and specialized teeth: Eudimorphodon and Dorygnathus had teeth designed to spear and hold prey; Dsungaripterus had bony jaws and broad, flattened teeth to winkle out shellfish and snails; and Pterodaustro had a comblike array of teeth, ideal for sieving plankton. The majority of pterosaur bones have been recovered from marine sedimentary rock deposits, suggesting these flying reptiles took advantage of the atmospheric updraft conditions of gentle and constant breezes along shorelines, as well as the abundant food of the marine environment. Pterosaur aerodynamics and flight characteristics have been studied in great detail, and they suggest pterosaurs were active, wing-flapping fliers, but also better gliders than are most modern bird species. Pterosaur anatomy suggests they were able to glide and soar over great distances and for extended periods of time under calm conditions, but that they were not well adapted for staying aloft under turbulent conditions. It is estimated that the pterosaur Pteranodon, who represents one of the high points in pterosaur evolution with a wingspan of over seven meters, could soar at speeds in excess of 30 kilometers per hour, continue gliding aloft for nearly twenty hours, and possibly cover distances of over 750 kilometers without landing. The greatest number of pterosaur bones have been recovered from the Kansas marine chalk deposits of North America. Over eight hundred skeletal fragments have been found there. While many of the remains suggest these Kansas pterosaurs died nonviolently, other bones suggest the pterosaurs were eaten by marine reptiles. Apparently, pterosaurs swooping low to snatch prey fromthe ocean's surface were often in turn preyed upon by larger marine reptiles or sharks.

Pterosaur Facts

Principal Terms
archosaurs: diapsid reptiles whose skeletal evolution distinguishes them from the diapsid lepidosaurs
Mesozoic Era: the middle era of the Phanerozoic eon, 250 million to 65 million years ago
patagium: a soft, flexible membrane

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