Why Are Pterosaur Fossils Rare?

This fossil of a young Pterodactylus antiquus was found in the layers of limestone near Solnhofen, Germany, an area known for its rich fossil beds. Pterosaur bones are fragile, so they rarely form fossils this clear and complete. 
© AMNH/C. Chesek

Few pterosaurs lived close to the places where fossils tend to form. Their fragile bones 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. 

IMPERFECT EVIDENCE

Of all the pterosaurs that ever lived, only a minuscule fraction died under the right conditions to be captured as fossils. Even fewer are preserved intact. Pterosaur bones were thin and fragile, much like bird bones, and they often drifted apart, shattered, or became scrambled before they could be preserved.

Pterosaur fossils are also easily damaged when extracted, transported, or prepared for study or display. Evidence is scarce, and each fossil offers just a hint of the wide array of pterosaurs that once populated the globe.

This cast of a poorly preserved Preondactylus buffarinii fossil shows a relatively short skull, jaws studded with triangular teeth, and a long, straight tail that is broken and bent forward. Parts of wrist, hand, wing finger, and toes survive as fossilized bone.
© AMNH/C. Chesek

Preondactylus buffarinii, found near Preone, a village in the Italian Alps, is one of the oldest pterosaurs, dating back around 220 million years. The most complete specimen discovered so far broke into several pieces when it was removed from the surrounding rock, and most of the brittle skeleton was lost. All that remain are small fragments and an imprint of the rest of the bones.

WELL PRESERVED PTEROSAUR

Around 110 million years ago, this adult pterosaur died and fell into a lagoon in what’s now Brazil. Eventually the animal’s body was buried by fine sediments, which slowed down decomposition and allowed fossilization to begin. 

As the mud gradually settled, a hard shell formed around the remains and protected them. As a result, this animal was exquisitely preserved as a three-dimensional fossil. Millions of years later, when the hard shell—called a nodule—was cracked open, this Anhanguera santanae was discovered. 

Most bones are flattened during fossilization, but the skeleton of this pterosaur was protected inside a hard shell, called a nodule, that formed as mud around the animal’s remains gradually turned to stone.
© AMNH/C. Chesek

This specimen was discovered in the Romualdo Formation in Brazil’s Araripe Basin. Many thousands of three-dimensional fossils have been discovered there, including pterosaurs, fish, reptiles, and plants.

Find out more about how fossils form—and how scientists read fossil evidence for clues about animal behavior—in Pterosaurs: Flight in the Age of Dinosaurs.