? PterosaurConservation status: Fossil | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| [image] A Pteronodon from a 1914 study. | ||||||||||
| Scientific classification | ||||||||||
| ||||||||||
| Suborders | ||||||||||
| Rhamphorhynchoidea Pterodactyloidea |
Pterosaurs (TEH-row-sore, "winged lizards," often incorrectly referred to as "pterodactyls" (TEH-row-DAK-tils) 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). The earlier species had long, fully-toothed jaws and long tails, while later forms had a stump for a tail, no teeth and a jaw more like a beak than the elongated jaw of the earlier species. Pterosaurs are classified as archosaurs, along with crocodiles and dinosaurs (and the dinosaurs' descendants, the birds).
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 then crushing them. This created three dimensional fossils for paleontologists to study. The first find in the Araripe Plateau was discovered in 1974.
[image]
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").
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.
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. The larger, bulkier pterosaurs with porportionately smaller hindlimbs and massive forebodies are (almost?) universally thought to have moved about on all fours while on the ground, like modern bats.
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 per cent 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 per cent 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.
It is believed that competition with early bird species may have resulted in the extinction 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 larger animals all died, including the pterosaurs.
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 properly described.
The Rhamphorhynchoidea are a paraphyletic group, so with the increasing use of Cladistics it has fallen out of favor.