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Pterosaurs
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The smallest Pterosaurs were about the size of a small bird, but the largest, such as Quetzalcoatlus had a wingspan of as much as 36 feet (11 meters). Most (or perhaps even) all smaller Pterosaur species seemed to have died out before the end of the Cretaceous period, and it is thought that this might have been due to competition from birds. By the time of the Cretaceous-Tertiary mass extinction, only the Pterosaurs survived, and these of course died out during that extinction. Pterosaurs evolved flight independently and separately from birds, but incorporated a number of bird-like features. Their bones were hollow and air filled, which reduced their weight, that had breastbone to which they flight muscles were attached, and they seem to have brain adaptations which would have helped them fly. It was once thought that Pterosaurs were mainly gliders, but today many scientists believe that atleast some species were active flyers. Pterosaurs wings were a membrane that stretched from an elongated fourth finger of each arm, and joined to the body. Some paleontologists have argued that the wing membrane would also have joined to the hind limbs, but others say this would not have been the case - it is also possible that the extent of the wing membrane depended on the particular species. It is also known that atleast some Pterosaurs had webbed feet, and while it is possible that these may have been used for swimming, it is also possible that they may have assisted in flying. There is also evidence that at least some species of Pterosaurs had hair. Pterosaur hair evolved independently of mammalian hair, and would have a different structure, although similar function to that of a mammals. The presence of hair suggests that Pterosaurs were probably warm-blooded ("endothermic"). When walking on the ground, Pterosaurs probably had a semi-erect posture. There was once much debate about whether they walked on two legs (bipedally) or four legs (quadrupedally), but fossil tracks that have been found, show they were quadrupeds. The first Pterosaur fossil was found in 1784 by Cosimo Collini, who believed he had found a sea creature (although the eminent naturalist Georges Cuvier suggested that Pterosaurs were flying creatures as early as 1801, the aquatic hypothesis about the creatures continued to be supported by some scientists until at least the 1830s). Other early discoveries include a find of the Pterosaur Dimorphodon by Mary Anning in Lyme Regis, England in 1828. Today, at least 60 different genera of Pterosaurs are known, and fossil have been found in every continent except Antarctica. Since Pterosaur bones were hollow, unfortunately they tended to be crushed when buried under sediments, so many fossils are poorly preserved. However, fortunately there is an exception - for some unknown reason the bones in Pterosaurs found in the Araripe Plateau in Brazil were not crushed during the fossilization process. Additionally, as already noted, fossil Pterosaur trackways have been found. Furthermore, one fossil Pterosaur egg has been found - which although squashed, was not cracked (suggesting Pterosaur eggs were soft and leathery) - contained an embryo containing well-developed wing membranes. Because Pterosaur fossils are not always well-preserved, and there are many gaps in the fossil record, there has been much debate about how Pterosaurs evolved, and how to classify them. Traditionally, Pterosaurs are generally classified into two suborders - the Rhamphorhynchoidea, which were "primitive" Pterosaurs, with long tails and fingers adapted to climbing - and the Pterodactyloidea, which were "advanced" Pterosaurs, with shorter tails, long wing metacarpals. Fossils of Pterosaurs have been found around the world including in England, Norway, the united States, Mexico, South America, and Australia. Pterosaurs Timeline:Pterosaurs were winged reptiles that lived between 220 and 65 million years ago
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