Ornithocheiroid Pterosaurs
Ornithocheiroidea
Summary 2
Pterosaurs (/ˈtɛrəˌsɔːr, ˈtɛroʊ-/;[4][5] from the Greek πτερόσαυρος, pterosauros, meaning "winged lizard") were flying reptiles of the extinct clade or order Pterosauria. They existed during most of the Mesozoic: from the late Triassic to the end of the Cretaceous (228 to 66 million years ago[6]). Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger.[7]
Early species had long, fully toothed jaws and long tails, while later forms had a highly reduced tail, and some lacked teeth. Many sported furry coats made up of hair-like filaments known as pycnofibers, which covered their bodies and parts of their wings. Pterosaurs spanned a wide range of adult sizes, from the very small anurognathids to the largest known flying creatures of all time, including Quetzalcoatlus and Hatzegopteryx.[8][9][10]
Pterosaurs are often referred to in the popular media and by the general public as "flying dinosaurs", but the term "dinosaur" is restricted to just those reptiles descended from the last common ancestor of the groups Saurischia and Ornithischia (clade Dinosauria, which includes birds), and current scientific consensus is that this group excludes the pterosaurs, as well as the various groups of extinct marine reptiles, such as ichthyosaurs, plesiosaurs, and mosasaurs.[11]
Unlike these other reptiles, pterosaurs are nonetheless more closely related to birds and dinosaurs than to crocodiles or any other living reptile.[b] Pterosaurs are also colloquially referred to as pterodactyls, particularly in fiction and by journalists.[12] However, technically, pterodactyl only refers to members of the genus Pterodactylus,[13] and more broadly to members of the suborder Pterodactyloidea of the pterosaurs.[14][15]
Pterosaur wings were formed by membranes of skin and other tissues. The primary membranes attached to the extremely long fourth finger of each arm and extended along the sides of the body to the ankles.
While historically thought of as simple leathery structures composed of skin, research has since shown that the wing membranes of pterosaurs were highly complex dynamic structures suited to an active style of flight. The outer wings (from the tip to the elbow) were strengthened by closely spaced fibers called actinofibrils.[17] The actinofibrils themselves consisted of three distinct layers in the wing, forming a crisscross pattern when superimposed on one another. The function of the actinofibrils is unknown, as is the exact material from which they were made. Depending on their exact composition (keratin, muscle, elastic structures, etc.), they may have been stiffening or strengthening agents in the outer part of the wing.[18] The wing membranes also contained a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels.[19]
As shown by cavities in the wing bones of larger species and soft tissue preserved in at least one specimen, some pterosaurs extended their system of respiratory air sacs (see Paleobiology section below) into the wing membrane.[20]
Most pterosaur skulls had elongated jaws with a full complement of needle-like teeth.[33] In some cases, fossilized keratinous beak tissue has been preserved, though in toothed forms, the beak is small and restricted to the jaw tips and does not involve the teeth.[34] Some advanced beaked forms were toothless, such as the pteranodonts and azhdarchids, and had larger, more extensive, and more bird-like beaks.[33]
Unlike most archosaurs, the nasal and antorbital openings of pterodactyloid pterosaurs merged into a single large opening, called the nasoantorbital fenestra. This feature likely evolved to lighten the skull for flight.[33]
Some species of pterosaurs featured elaborate crests. The first and perhaps best known of these is the distinctive backward-pointing crest of some Pteranodon species, though a few pterosaurs, such as the tapejarids and Nyctosaurus, sported extremely large crests that often incorporated keratinous or other soft tissue extensions of the bony crest base.
Since the 1990s, new discoveries and more thorough study of old specimens have shown that crests are far more widespread among pterosaurs than previously thought, due mainly to the fact that they were frequently extended by or composed completely of keratin, which does not fossilize as often as bone.[19] In the case of pterosaurs like Pterorhynchus and Pterodactylus, the true extent of these crests has only been uncovered using ultraviolet photography.[34][35] The discovery of Pterorynchus and Austriadactylus, both crested "rhamphorhynchoids", showed that even primitive pterosaurs had crests (previously, crests were thought to be restricted to the more advanced pterodactyloids).[19]
Fontes e Créditos
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- Adaptado por calgaryzoo de uma obra de (c) Wikipedia, alguns direitos reservados (CC BY-SA), https://en.wikipedia.org/wiki/Ornithocheiroidea
