Pterosaurs
Pterosaurs, often referred to as "winged reptiles," were a group of flying reptiles that lived during the Mesozoic Era, existing from around 225 million years ago until about 65 million years ago. As members of the Archosauria clade, which also includes dinosaurs and modern birds, pterosaurs are notable for being one of the first vertebrate groups to evolve active flight. They are distinct from dinosaurs and are characterized by their unique wing structure, which was supported by an elongated fourth finger and comprised of a tough, membranous patagium. Pterosaurs varied widely in size, from small species like Pterodactylus, with a wingspan akin to that of a songbird, to the enormous Quetzalcoatlus, whose wingspan could reach fifteen meters.
Pterosaur classification is complex and ongoing due to limited fossil records, traditionally divided into two main groups: rhamphorhynchoids and pterodactyloids. These flying reptiles exhibited diverse feeding adaptations, with some having specialized teeth for various diets, including plankton and shellfish. Evidence suggests pterosaurs were likely warm-blooded and shared features such as pycnofibers, which might have provided insulation. Their aerodynamic capabilities allowed for efficient gliding and soaring, enabling them to travel vast distances, although they were less adept in turbulent conditions. Fossil evidence shows that many pterosaurs thrived along coastlines, taking advantage of updrafts and abundant food resources in marine environments.
On this Page
Subject Terms
Pterosaurs
Type of animal science: Classification
Fields of study: Evolutionary science, paleontology, physiology
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 are 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 tree-dwelling 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. From the earliest scientific studies of pterosaurs, some fossil remains suggested certain pterosaurs may have been covered with short, thin fibers similar to fur, or even very fine feathers. By the 2010s, evidence pointed to virtually all pterosaur species having had fur-like structures known as pycnofibers on their bodies; the leading theory held that pycnofibers evolved independently from mammalian hair and dinosaurs' protofeathers. 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
Pterosaur classification is the subject of ongoing debate, partly due to the scarcity of fossils meaning many relationships between species must be speculated. Traditionally, pterosaurs were commonly divided into two main groups: the rhamphorhynchoids, first appearing during the Triassic, and the pterodactyloids, appearing some 108 million years later. The Rhamphorhynchoidea were mainly distinguished by their long tails, and were considered primitive compared to the shorter-tailed Pterodactyloidea. However, cladistic classification has led this simple binary division to fall out of favor among scientists, even as it remains common in popular literature on pterosaurs. Newer classification models include more subdivisions of evolutionarily earlier species.
Because of the lack of agreement on the exact classification of pterosaurs, many species and groups continue to be described based on morphological features. Pterodactyloidea, such as those in the genus Pterodactylus, are known to have evolved head crests, in some cases to extreme degrees. Some 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 many species 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, which 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 from the ocean’s surface were often in turn preyed upon by larger marine reptiles or sharks.
Bibliography
Monastersky, Richard. "Pterosaurs—Lords of the Ancient Skies." National Geographic, 2017, science.nationalgeographic.com/science/prehistoric-world/pterosaurs/. Accessed 20 Oct. 2017.
Norman, David. Prehistoric Life: The Rise of the Vertebrates. New York: Macmillan, 1994. A richly illustrated book and good general reference, outlining evolutionary development, anatomy, and ongoing scientific debates concerning the life history and ecological function of pterosaurs within the Mesozoic environment.
Padian, Kevin. "Pterosaurs: Were They Functional Birds or Functional Bats?" In Biomechanics in Evolution, edited by J. M. V. Rayner and R. J. Wootton. New York: Cambridge University Press, 1991. Suggests the course of vertebrate flight evolution is best supported by phylogenetic analysis of biomechanics and functional morphology.
Russell, Dale A. An Odyssey in Time: The Dinosaurs of North America. Toronto, Ontario: University of Toronto Press, 1989. This book provides a general overview of pterosaur fossil discoveries in North America, and gives some general information on pterosaur behavior based on paleoecology of the rock formations in which the fossils were found.
"Sciencespeak: Pycnofiber." Phenomena, National Geographic, 23 Mar. 2015, phenomena.nationalgeographic.com/2015/03/23/sciencespeak-pycnofiber/. Accessed 23 Oct. 2017.
Shipman, Pat. Taking Wing: Archaeopteryx and the Evolution of Bird Flight. New York: Simon & Schuster, 1998. The chapter "Pathways to the Skies" gives a very good overview of the theories surrounding the biomechanics and physiology of pterosaurs. The chapter also provides a brief history of the study of pterosaurs, and the historical use of comparative anatomy to define pterosaur morphology and behavior.
"What Is a Pterosaur?" American Museum of Natural History, 2017, www.amnh.org/exhibitions/pterosaurs-flight-in-the-age-of-dinosaurs/what-is-a-pterosaur/. Accessed 20 Oct. 2017.
Witton, Mark P. Pterosaurs: Natural History, Evolution, Anatomy. Princeton UP, 2013.