Why Pterosaur Fossils Are So Rare
In 1784 the Italian naturalist, Cosimo Collini, discovered and described the first pterosaur fossil. However, Collini misinterpreted his find, believing that he had discovered a seagoing creature that used its long front limbs as flippers. It was not until 1801 that Georges Cuvier realized that pterosaurs were actual flying creatures. Pterosaur is derived from the Greek word meaning “winged lizard”. Although often referred to in the media and by the general public as a flying dinosaur, technically, a pterosaur is not a dinosaur. The pterosaur was the first vertebrate to have evolved the ability to fly. Certain larger species of pterosaurs are considered the largest flying creatures to have ever lived on our planet. Pterosaurs were found on the Earth from the late Triassic to the end of the Cretaceous Period.
The anatomy of a pterosaur was highly modified from that of their reptilian ancestors to enable flight. Like birds, pterosaur had bones that were hollow and air-filled, a keeled breastbone that was developed for the attachment of flight muscles and an enlarged brain. Not surprising, all of these adaptations are generally associated with the ability to fly. The wing of the pterosaur were formed primarily from a membrane of skin and muscle that stretched from the ankle to an elongated fourth finger. The pterosaur had a tail, the length varying with the species. Most pterosaur had elongated jaws, some with sharp teeth and some toothless species with more of a beak. However, in only a few cases were these keratinous beaks preserved in the fossil record. Pterosaurs are also well-known for having elaborate crests that incorporated keratinous or other soft tissue extensions with the bony crest base. However, such soft tissues do not fossilize as often as bone. In some cases, the extent of these crests were only uncovered using ultraviolet photography.
Fossilized pterosaur eggs are also very rare. The first known pterosaur egg was 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, suggesting that pterosaur eggs had leathery shells, like modern lizards. Another pterosaur egg described in 2011 also had a leathery shell. Like modern reptiles but unlike birds, the pterosaur eggs were fairly small compared to the size of the mother. A study of the pterosaur eggshell structure and chemistry published in 2007 suggest that pterosaurs probably buried their eggs, like modern crocodiles and turtles.
Amazingly, fossils of pterosaurs just several days old (called flaplings) have been found, as well as preserved pterosaur embryos. The latter had well developed wing membranes, suggesting pterosaurs were ready to fly soon after birth. The bones of the young pterosaur show a relatively high degree of hardening (ossification) for their age, and wing proportions of young pterosaurs are similar to that of adults. In fact, many pterosaur flaplings had been considered adults and placed in separate species in the past. Additionally, flapling fossils are normally found in the same sediments as adults and juveniles of the same species, while all were found in deep aquatic environment far from shore.
Few pterosaurs lived close to the areas where fossils tend to form. The fragile bones of the pterosaur preserved poorly, so pterosaur fossils are frequently incomplete. To form a picture of a particular species, paleontologists must often gather information from several fossils, or draw conclusions from related pterosaurs that are better known.