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Pterosaur

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

   iPterosaur

                    Fossil range: Triassic – Cretaceous

   Coloborhynchus piscator, a Late Cretaceous pterosaur.
   Coloborhynchus piscator, a Late Cretaceous pterosaur.

                             Conservation status

   Extinct (fossil)
                 Scientific classification

   Kingdom:   Animalia
   Phylum:    Chordata
   Class:     Sauropsida
   (unranked) Archosauria
   Order:     Pterosauria
              Kaup, 1834

                                  Suborders

   Rhamphorhynchoidea *
   Pterodactyloidea

   Pterosaurs (/ˈtɛ.rəˌsɔː(r)/, from the Greek "πτερόσαυρος", meaning
   winged lizards, often referred to as pterodactyls, from the Greek
   "πτεροδάκτυλος", meaning "winged finger" /ˌtɛ.rəˈdæk.tɪl/) were flying
   reptiles of the clade 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 sophisticated membrane of skin 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.

Fossil evidence

   Pterosaurs were first discovered in 1784 by the Italian naturalist
   Cosimo Collini. He initially believed that pterosaurs were aquatic
   animals, not flyers. In the 19th century Georges Cuvier proposed that
   pterosaurs flew.

   At least 60 genera of pterosaurs have been found, ranging from the size
   of a small bird to wingspans in excess of 10 meters (33 feet). 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. Most paleontologists now believe that
   pterosaurs were adapted for active flight, not just gliding as was
   earlier believed.

   Most pterosaur fossils did not preserve well. 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.
   The three dimensionally preserved skull of Anhanguera santanae, from
   the Santana Formation, Brazil.
   Enlarge
   The three dimensionally preserved skull of Anhanguera santanae, from
   the Santana Formation, Brazil.

Anatomy

   Pterosaurs were highly modified from their reptilian ancestors for the
   demands of flight.
   Pteranodon skeletal drawing from a 1914 scientific paper.
   Enlarge
   Pteranodon skeletal drawing from a 1914 scientific paper.

   Pterosaur wings were formed by membranes of skin and other tissues,
   strengthened by various types of closely spaced fibers. The membranes
   attached to the extremely long fourth finger of each arm and extending
   along the sides of the body. A novel bone called the pteroid connected
   to the wrist and helped to support a membrane (the propatagium) between
   the wrist and shoulder. The pteroid might have been able to swing
   forward to extend this membrane, although this is very controversial.
   In 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).

   Pterosaur's hip sockets were oriented facing slightly upwards, and the
   head of the femur (thigh bone) was only moderately inward facing,
   suggesting that pterosaurs had a semi-erect stance. It would have been
   possible to lift the thigh into a horizontal position during flight.

   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 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 is possible that, like
   these groups, different species of pterosaur had different wing
   designs. Many if not all pterosaurs also had webbed feet, and although
   these have been considered to be evidence of swimming, webbed feet are
   also seen in some gliding animals such as colugos (the "flying
   lemurs"), and may have had an aerodynamic function.

   Pterosaur bones were hollow and air filled, like the bones of birds.
   Unlike typical reptiles, pterosaurs had a keeled breastbone that was
   developed for the attachment of flight muscles and a brain that was
   more developed than comparable dinosaurs of similar sizes.

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 but not homologous to mammalian hair. Pterosaur hair is not
   true hair; it is a form of extremely thin fiberous "scales". 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, not unlike
   modern-day bats, an interesting example of convergent evolution. The
   presence of hair (and the demands of flight) imply that pterosaurs were
   warm-blooded (' endothermic').

Ground movement

   Pterodactylus kochi appears to be well adapted to walking on all fours.
   Enlarge
   Pterodactylus kochi appears to be well adapted to walking on all fours.

   There has been considerable debate in the past about whether pterosaurs
   moved about on the ground as quadrupeds or as bipeds. A large number of
   pterosaur trackways are now known, with a distinctive four-toed hind
   foot and three-toed front foot; these are the unmistakable prints of
   pterosaurs walking on all fours. However, it might be too much to
   conclude that all pterosaurs were quadrupedal, all the time.

   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.

Behaviour

   A 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. The wing membranes were unusally well developed for a
   hatchling in an egg, suggesting pterosaurs were ready to fly soon after
   birth, though whether a parent took care of them is unknown. Very young
   animals have been found in the Solnhofen limestone beds, where they
   presumably flew to the middle of a lagoon, fell in and drowned.

   A study of pterosaur brains using X-rays has revealed extraordinary
   information about their habits. Studying fossil pterosaur skulls is
   extremely difficult because they are so delicate, but Lawrence Witmer
   at Ohio University in Athens and his colleagues used X-ray CT scans to
   build up 3D images of the brains of two species. One striking finding
   was that the animals (Rhamphorhynchus muensteri and Anhanguera
   santanae) had massive flocculi. The flocculus is a brain region that
   integrates signals from joints, muscles, skin and the balance organs.

   The pterosaurs' flocculi occupied 7.5 % of the animals' total brain
   mass, more than in any other vertebrate. Birds have unusually large
   flocculi compared with other animals, but these only occupy between 1
   and 2 % of total brain mass. "It is just ridiculously large in
   pterosaurs," says Witmer.

   The flocculus sends out neural signals that produce small, automatic
   movements in the eye muscles. These keep the image on an animal's
   retina steady. Pterosaurs probably had such a large flocculus because
   of their large wing size. This extra area meant that there was a great
   deal more sensory information to process.

   Pterosaurs are known to have been attacked 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.

Evolution and extinction

   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 is not well understood. They are generally,
   but not universally, thought to be related to the Dinosauria on the
   basis of their ankle structure.

   They are thought to have evolved flight from some manner other than the
   'tree-down' route possibly taken by birds, because pterosaurs
   demonstrated no adaptations useful for tree living. Most scenarios have
   pterosaurs evolving from long-legged, ground-running ancestors like
   Scleromochlus or Sharovipteryx (a less likely scenario), both of which
   had webs of skin from long hind legs to their bodies or tails. This
   suggests a 'ground-up' evolution of flight or even a route that evolved
   by gliding from cliff-tops.

   It is believed by some that competition with early bird species may
   have resulted in the extinction of many of the pterosaurs. By the end
   of the Cretaceous, only large species of pterosaurs survived. The
   smaller species were extinct, and replaced by birds. At the end of the
   Cretaceous period, the great extinction which wiped out all dinosaurs,
   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. A lack of
   small pterosaurs in the fossil record could be explained by competition
   with birds or poor preservation due to the fragility of their
   skeletons.

   A recent dissertation by Momchil Atanassov describes two new specimens
   from the Late Triassic Dockum Formation of Texas that may reveal a lot
   of new information about the origins of pterosaurs. They still have yet
   to be formally described.

Taxonomy

   Classification of pterosaurs has traditionally 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 are organized into two suborders:
     * Rhamphorhynchoidea (Plieninger, 1901): A group of early, basal
       ("primitive") pterosaurs, many of which had long tails and short
       wing metacarpals. 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, so with the increasing use of cladistics it has
       fallen out of favour.

     * 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.

   For a comprehensive listing of the various classification schemes that
   have been proposed, please see List of pterosaur classifications.
     * ORDER PTEROSAURIA (extinct)
          + Suborder Rhamphorhynchoidea *
               o Family Dimorphodontidae
               o Family Anurognathidae
               o Family Campylognathoididae
               o Family Rhamphorhynchidae
          + Suborder Pterodactyloidea
               o Superfamily Ornithocheiroidea
                    # Family Ornithodesmidae
                    # Family Ornithocheiridae
                    # Family Pteranodontidae
                    # Family Nyctosauridae
               o Superfamily Ctenochasmatoidae
                    # Family Pterodactylidae
                    # Family Ctenochasmatidae
               o Superfamily Dsungaripteroidea
                    # Family Germanodactylidae
                    # Family Dsungaripteridae
               o Superfamily Azhdarchoidea
                    # Family Tapejaridae
                    # Family Azhdarchidae
                    # Family Tupuxuaridae

Well-known genera

   Examples of pterosaur genera include:
     * Dsungaripterus had a wingspan of 3 metres (10 feet), 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 feet), 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 12 metres (40 feet) but weighed
       only 50 kilograms (110 pounds), and 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.

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