Everything about Pterosaurs totally explained
Pterosaurs (from the
Greek πτερόσαυρος,
pterosauros, meaning "winged lizard", often referred to as
pterodactyls, from the Greek πτεροδάκτυλος,
pterodaktulos, meaning "winged finger" /ˌtɛrəˈdæktɨl/) were flying
reptiles of the
clade or
order Pterosauria. They existed from the late
Triassic to the end of the
Cretaceous Period (228 to 65
million years ago). Pterosaurs were the first
vertebrates to evolve flight. Their wings were formed by a membrane of skin, muscle, and other
tissues stretching from the
thorax to a dramatically lengthened fourth finger. Earlier species had long, fully-toothed jaws and long tails, while later forms had a highly reduced tail, and some lacked teeth. Pterosaurs spanned a wide range of adult sizes, from the very small
Nemicolopterus to the largest known flying creatures of all time, including
Quetzalcoatlus and
Hatzegopteryx.
Pterosaurs are sometimes referred to in the popular media as
dinosaurs, but this is incorrect. The term "dinosaur" is properly restricted to a certain group of
terrestrial reptiles with a unique upright stance (superorder Dinosauria), and therefore excludes the pterosaurs, as well as the various groups of extinct aquatic reptiles, such as
ichthyosaurs,
plesiosaurs, and
mosasaurs.
History of discovery
The first pterosaur
fossil was described by the
Italian naturalist
Cosimo Collini in 1784. Collini misinterpreted his specimen as a sea-going creature that used its long front limbs as paddles. A few scientists continued to support the aquatic interpretation even until 1830, when the German zoologist
Johann Georg Wagler suggested that
Pterodactylus used its wings as flippers.
Georges Cuvier first suggested that pterosaurs were flying creatures in 1801, and coined the name "
Ptero-dactyle" 1809 for a specimen recovered in Germany; however, due to the standardization of scientific names, the official name for this species became
Pterodactylus, though the name "pterodactyl" continued to be popularly applied to all members of this first specimen's order.
Since the first pterosaur
fossil was discovered in the late Jurassic
Solnhofen limestone in 1784, twenty-nine kinds of pterosaurs have been found in those deposits alone. A famous early
UK find was an example of
Dimorphodon by
Mary Anning, at
Lyme Regis in 1828.
Most pterosaur fossils are poorly preserved. Their
bones were hollow and, when
sediments piled on top of them, the bones were flattened. The best preserved fossils have come from the
Araripe Plateau,
Brazil. For some reason, when the bones were deposited, the sediments encapsulated the bones, rather than crushing them. This created three-dimensional fossils for paleontologists to study. The first find in the Araripe Plateau was made in 1974.
Most
paleontologists now believe that pterosaurs were adapted for active
flight, not just
gliding as was earlier believed. Pterosaur fossils have been found on every continent except
Antarctica. At least 60
genera of pterosaurs have been found to date, ranging from the size of a small bird to wingspans in excess of 10
meters (33
feet).
Anatomy and palaeobiology
The anatomy of pterosaurs was highly modified from their reptilian ancestors for the demands of flight. Pterosaur
bones were hollow and air filled, like the bones of
birds. They had a keeled
breastbone that was developed for the attachment of flight
muscles and an enlarged
brain that shows specialised features associated with flight.
Wings
Pterosaur wings were formed by membranes of skin and other tissues, strengthened by various types of closely spaced fibers called actinofibrillae. The membranes attached to the extremely long fourth
finger of each
arm and extended along the sides of the body. A bone unique to pterosaurs, known as the pteroid, connected to the wrist and helped to support a membrane (the propatagium) between the wrist and shoulder. It has been argued that the pteroid might have been able to swing forward to extend this membrane,, although this is strongly contested by other researchers. In some later pterosaurs, the backbone over the shoulders fused into a structure known as a
notarium, which served to stiffen the torso during flight, and provide a stable support for the
scapula (shoulder blade).
There has been considerable argument among paleontologists about whether the wings attached to the hindlimbs as well. Fossils of the rhamphorhynchoid
Sordes, the
anurognathid Jeholopterus, and a pterodactyloid from the
Santana Formation seem to demonstrate that the wing membrane did attach to the hindlimbs, at least in some species. However, modern
bats and
flying squirrels show considerable variation in the extent of their wing membranes and it's possible that, like these groups, different species of pterosaur had different wing designs. Indeed, analysis of pterosaur limb proportions shows that there was considerable variation, possibly reflecting a variety of wing-plans. Many if not all pterosaurs also had webbed feet, and although these have been considered to be evidence of swimming, they may have had an aerodynamic function.
Hair
There is no fossil evidence of feathers, but pterosaurs were unique among reptiles in that at least some of them were covered with
hair, similar to but not
homologous with
mammalian hair. Pterosaur "hair" isn't true hair as seen in mammals, but a unique structure that developed a similar appearance through
convergent evolution. Although in some cases fibers in the wing membrane have been mistaken for hair, some fossils such as those of
Sordes pilosus (the "hairy demon") do show the unmistakable imprints of hair on the head and body,
It has been suggested that smaller pterosaurs with longer hindlimbs such as
Dimorphodon might have walked or even run bipedally, in addition to flying, not unlike modern
road runners. Other small pterosaurs such as
Rhamphorhynchus may have scurried around on all fours. Larger pterosaurs with proportionately smaller hindlimbs and massive forebodies are generally thought to have moved about on all fours while on the ground. All known pterosaur footprints match the feet of pterosaurs adapted to wading and sifting for their food. Tracks that can be matched to soaring and tree-clinging pterosaurs are not known.
Predation
Pterosaurs are known to have been eaten by
spinosaurs. In the
1 July 2004 edition of
Nature, paleontologist
Eric Buffetaut discusses an early Cretaceous fossil of three cervical
vertebrae of a pterosaur with the broken tooth of a spinosaur embedded in it. The vertebrae are known not to have been eaten and exposed to digestion, as the joints still articulated.
Reproduction
Very little is known about pterosaur reproduction. A single pterosaur egg has been found in the quarries of Liaoning, the same place that yielded the famous 'feathered' dinosaurs. The egg was squashed flat with no signs of cracking, so evidently the eggs had leathery shells, as in modern lizards. The embryo's wing membranes were well developed, suggesting pterosaurs were ready to fly soon after birth. This is corroborated by very young animals found in the Solnhofen limestone beds, where they presumably flew to the middle of a lagoon, fell in and drowned. It isn't known whether pterosaurs practised parental care, but their comparatively early flight capabilities suggest the young were not completely dependent on parents as most birds are.
A study of pterosaur eggshell structure and chemistry published in 2007 indicated that it's likely pterosaurs buried their eggs, like modern
crocodile and
turtles. Egg-burying would have been beneficial to the early evolution of pterosaurs, as it allows for more weight-reducing adaptations, but this method of reproduction also would have put limits on the variety of environments pterosaurs could live in, and may have disadvantaged them when they began to face ecological competition from
birds. The alternative would be for the mother to retain the egg within the body until just prior to hatching, as some lizards do, but archosaurs are incapable of.
Evolution and extinction
Origins
Because pterosaur
anatomy has been so heavily modified for flight, and
immediate "missing link" predecessors have not so far been described, the ancestry of pterosaurs isn't well understood. Several hypotheses have been advanced, with the most common in recent years being links to
ornithodirans like
Scleromochlus, an ancestry among the
archosauriforms like
Euparkeria (a more traditional view), or related to
prolacertiformes like
Sharovipteryx. At least one pterosaur specialist, David Unwin, finds none of these options convincing for various anatomical reasons.
Phylogeny and classification
Classification of pterosaurs has historically been difficult, because there were many gaps in the
fossil record. Many new discoveries are now filling in these gaps and giving us a better picture of the evolution of pterosaurs. Traditionally, they're organized into two
suborders:
Rhamphorhynchoidea (Plieninger, 1901): A group of early, basal ("primitive") pterosaurs, many of which had long tails and short metacarpal bones in the wing. They were small, and their fingers were still adapted to climbing . They appeared in the late Triassic period, and lasted until the late Jurassic. Rhamphorhynchoidea is a paraphyletic group (since the pterodactyloids evolved directly from them and not from a common ancestor), so with the increasing use of cladistics it has fallen out of favor in most technical literature.
Pterodactyloidea (Plieninger, 1901): The more derived ("advanced") pterosaurs, with short tails and long wing metacarpals. They appeared in the middle Jurassic period, and lasted until the Cretaceous-Tertiary extinction event wiped them out at the end of the Cretaceous.
Listing of families and superfamilies within Pterosauria, after Unwin 2006.
ORDER PTEROSAURIA (extinct)
The precise relationships between pterosaurs is still unsettled. However, several newer studies are beginning to make things clearer. Cladogram simplified after Unwin.
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|label2= Dsungaripteroidea
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|label3= Azhdarchoidea
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Extinction
It is believed by some that competition with early avian dinosaur species may have resulted in the extinction of many of the pterosaurs. By the end of the Cretaceous, only large species of pterosaurs are known. The smaller species seem to have become extinct, their niche filled by birds, though a lack of small pterosaurs in the fossil record could also be a result of poor preservation due to the fragility of their skeletons. At the end of the Cretaceous period, the great extinction which wiped out all non-avian dinosaurs plus most avian dinosaurs as well, and many other animals, seemed to also take the pterosaurs. Others suggest that most pterosaurs were specialised for an ocean-going lifestyle. Consequently, when the K-T mass-extinction severely affected marine life that most pterosaurs fed on, they went extinct.
Well-known genera
Examples of pterosaur genera include:
Dsungaripterus had a wingspan of 3 metres (10 ft), an unusual bony crest running along its snout, and long, narrow, curved jaws with a pointed tip. It lived during the early Cretaceous period.
Pteranodon was 1.8 metres (six feet) long, with a wingspan of 7.5 m (25 ft), and lived during the late Cretaceous period.
Pterodactylus had a wingspan of 50 to 75 centimeters (20 to 30 inches), and lived during the late Jurassic on lake shores.
Pterodaustro was a Cretaceous pterosaur from South America with a wingspan around 1.33 metres and with over 500 tall, narrow teeth, which were presumably used in filter-feeding, much like modern flamingos. Also like flamingos, this pterosaur's diet may have resulted in the animal having a pink hue. It was South America's first pterosaur find.
Quetzalcoatlus had a wingspan of 10-11 metres (33-36 feet), and was among the largest flying animals ever. It lived during the late Cretaceous period.
Rhamphorhynchus was a Jurassic pterosaur with a vane at the end of its tail, which may have acted to stabilise the tail in flight.
Pterosaurs in popular culture
Pterosaurs are a staple of popular culture. While the generic term "pterodactyl" is often used to describe these creatures, the animal depicted is frequently a Pteranodon or other specific species of pterosaur, or a fictionalized hybrid of several species. Many children's toys and cartoons feature "pterodactyls" with Pteranodon-like crests and long, Rhamphorhynchus-like tails and teeth, a combination that never existed in nature. However, at least one type of pterosaur did have at least the Pteranodon-like crest and teeth--the Ludodactylus, a name that means "toy finger" for its resemblance to old, inaccurate children's toys. Notable examples of older fictional works featuring pterosaurs include Arthur Conan Doyle's book The Lost World and the 1933 film King Kong.
Living pterosaur hoax
It was reported in an article in The Illustrated London News (February 9, 1856, page 166) that, in 1856, workmen laboring in a tunnel for a railway line, between Saint-Dizier and Nancy, in France, were cutting through Jurassic limestone when a large creature stumbled out from inside it. It fluttered its wings, made a croaking noise and dropped dead. According to the workers, the creature had a wingspan, four legs joined by a membrane, black leathery skin, talons for feet and a toothed mouth. A local student of paleontology identified the animal as a pterodactyl. The report had the animal turn to dust, as soon as it had died.
This incredible hoax was stimulated in part by contemporary Franco-Prussian palaeontological rivalry. The Solnhofen limestone from Bavaria (in which Archaeopteryx would later be discovered) was producing many prized fossils, each of which was proudly announced by German paleontologists. The tunnel in question was through limestone of similar age to the Solnhofen Limestone, so it presented an opportunity for a shocking story by the French.
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