Not a Bird, Not a Dinosaur: What Is a Pterosaur?

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What is a pterosaur? It sounds like such a simple question.

But the answer, as you learn in the new exhibition Pterosaurs: Flight in the Age of Dinosaurs, was by no means obvious when the first pterosaur skeleton was discovered in the mid-1700s, in the Solnhofen limestone quarry in Germany.

Pterodactylus Mirror Image Fossil 700.309
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

Perhaps, early observers theorized, that specimen’s long skinny arm-and-finger bones were for swimming? Or was it some kind of toothed, clawed, winged bird? Or even a mammal? Debates raged, even after 1801, when the great French anatomist Georges Cuvier analyzed drawings of the skeleton and determined the animal to be something new to science: a flying reptile that Cuvier later named ptero-dactyle (wing finger in Greek), whose wings were composed of a shortened upper arm bone, along with a dramatically elongated fourth finger that likely supported a wing membrane. 

Since Cuvier’s time, the fossil record has revealed much more about these extinct reptiles, which lived from about 220 million years ago to the end of the late Cretaceous period 66 million years ago, disappearing at the same time as large dinosaurs in a mass extinction event.

Fossil of a Pterosaur head and beak
© AMNH/C. Chesek

Still, although pterosaurs may often be grouped with dinosaurs in children’s picture books, they are not dinosaurs. “Dinosaurs are characterized by a set of anatomical features pterosaurs don’t have,” explains Mark Norell, the curator of the exhibition and chair of the Division of Paleontology, including a hole in the hip socket.

Today’s scientific consensus is that pterosaurs are nonetheless more closely related to dinosaurs, whose living descendants are birds, than to any other group, including the next-closest, crocodiles. What is also clear is that pterosaurs were the first vertebrates to fly—an amazing feat. Tiny, invertebrate insects had long since taken to the air, but nothing as large as a four-legged vertebrate had attempted such a thing.

They are the most fabulous creatures that ever existed! I am not exaggerating,” says Alexander Kellner, the exhibition’s co-curator, who is based at the Museu Nacional in Rio de Janeiro and is a research associate at the Museum. “They made the first attempts among vertebrates to conquer the air—they were the first to develop powered flight,” that is, the type of sustained flight that evolved, later and independently, in birds and bats.

This story is adapted from an article in the Spring 2014 issue of Rotunda, the Member magazine.