Pterosaur

Pterosaurs were flying reptiles that belonged to the order Pterosauria. They are unique has being the first group of vertebrates to evolve powered flight, existing from the late Triassic to the extinction at the end of the Cretaceous. They are often erroneously identified as dinosaurs.

Description
The pterosaur body plan was radically different from that of their reptilian ancestors in order to meet the requirements that flight presented.

Wings
The wings of pterosaurs were composed of skin membranes, and were attached the elongated fourth finger of each front limb. They were strengthened by small fibers called actinofibrils.

Head
Most pterosaurs had needle-like teeth situated in their jaws, although some more advanced forms were toothless. Many individuals possessed keratinous beaks.

Some pterosaurs are well known for their elaborate head crests. Nyctosaurus possessed a head crest measuring up to 55 centimeters in height, which is very large in comparison to the rest of the animal. Although crests were first thought to be limited to more advanced forms of pterosaurs, it has been shown through new fossil evidence and use of ultraviolet photography that even primitive pterosaurs had some type of crest on their heads.

Integument
Some pterosaurs were covered with integumentary filaments called pycnofibres (meaning "dense filament", which was similar to mammalian hair. Only a couple genera have been found to possess this, such as Sordes and Jeholopterus, but they provide implied evidence that most or all pterosaurs were endothermic.

Classification and Evolution
In general, pterosaurs have been traditionally classified into two groups: Rhamphorhynchoidea and Pterodactyloidea (loosely defined as "primitive" and "advanced" pterosaurs, respectively).

The origin of pterosaurs is not completely understood, although is has been proposed that they were a type of ornithodiran and thus closely related to dinosaurs and other archosaurs.

History
The first pterosaur to ever be discovered, Pterodactylus, was originally described in 1784 as a type of sea creature. As better fossils were found and more people started to study them, however, it soon became clear that these were creatures designed for an aerial life.

Flight
Exactly how pterosaurs could fly is not yet understood and a point of contention. Some scientists have even claimed that it would be impossible for pterosaurs to stay aloft due to their body proportions. Mark Witton has suggested that they used a vaulting mechanism to take off into the air, which would be an easy feat due to their powerful forelimbs.

Ground movement
There used to be considerable debate whether pterosaurs were bipedal or quadrupedal when moving on the ground. However, pterosaur trackways have revealed that at least some species moved in a quadrupedal fashion. Footprints from azhdarchids show that some pterosaurs walked with their legs almost vertically under the body, much like modern mammals and birds.

Reproduction
Pterosaur eggs are very rare, and have only been discovered in the past few years. The first known pterosaur egg was discovered in 2004 in Liaoning, China. The fact that the egg was flattened but not broken suggests that pterosaur eggs had leathery shells. This hypothesis is supported by an egg from the pterosaur Darwinopterus found in 2011. Analysis of pterosaur eggshell structure and chemistry has suggested that pterosaurs buried their eggs like modern turtles and crocodilians.

Baby pterosaur fossils are more common, and show that young animals were well developed and almost indistinguishable from adults besides their size.

In popular culture
Pterosaurs have been long depicted beside dinosaurs in popular culture, and are often mistakenly identified as dinosaurs. Unlike the dinosaurs, however, popular depictions of pterosaurs have remained largely unchanged since the 1960s. The term "pterodactyl" is often used to describe these animals, although when used correctly the word is simply a name for Pterodactylus.