The question of what dinosaur flew is a common misconception in paleontology, pointing to a creature that soared through Mesozoic skies but was not technically a dinosaur. The flying reptiles that dominated the air belonged to an entirely separate evolutionary branch. The animal most people picture is closely related to dinosaurs, sharing a common ancestor, but it did not belong to the Dinosauria group.
The Answer: Pterosaurs
The definitive name for the extinct flying reptiles is Pterosaurs, belonging to the order Pterosauria, which translates to “winged lizards.” These animals were the first vertebrates to evolve powered flight, appearing in the Late Triassic period, long before birds took to the air. Pterosaurs existed throughout the entire Mesozoic Era, from about 228 million years ago until the mass extinction event 66 million years ago.
Their unique adaptation for flight involved a wing membrane, known as the patagium, which stretched from the torso and arms to the ankle. This membrane was primarily supported by a dramatically elongated fourth finger on each forelimb, a skeletal structure unlike that of any other flying animal. Pterosaurs developed hollow, air-filled bones, similar to those of birds, which helped minimize body weight.
Pterosaurs also possessed a large, keeled breastbone, or sternum, which provided an anchor point for powerful flight muscles. This group displayed an enormous range in size, from sparrow-sized forms like Anurognathus to giants like Quetzalcoatlus, which had wingspans reaching up to 35 feet. Common examples include the long-tailed Rhamphorhynchus and the later, toothless Pteranodon.
Why Pterosaurs Are Not Dinosaurs
The separation between Pterosaurs and Dinosaurs is based on specific skeletal features that classify an animal as belonging to the Dinosauria clade. Both Pterosaurs and Dinosaurs are members of the larger Archosaur group, which also includes crocodiles, meaning they share a distant common ancestor. They evolved along distinct evolutionary paths, branching off from that ancestor approximately 250 million years ago.
True dinosaurs are characterized by a unique hip structure featuring an open hip socket, or acetabulum, which allows for a fully upright posture where the legs are held directly beneath the body. Pterosaurs lacked this open socket and possessed a different arrangement of limb bones, resulting in a more sprawling or semi-erect leg posture. Dinosaurs also had a long crest on their upper arm bone, the humerus, which is absent in Pterosaurs.
These anatomical differences confirm that Pterosaurs are not simply flying dinosaurs but represent a parallel lineage of reptiles that independently achieved flight. Pterosaurs and dinosaurs co-existed for millions of years, but the absence of these skeletal markers means that classifying Pterosaurs as dinosaurs is scientifically incorrect.
The Actual Flying Dinosaurs
The scientifically correct answer to the question of what dinosaur flew is the group known as Avian Dinosaurs, which are modern birds. Birds are the direct descendants of a specific lineage of small, feathered, bipedal theropods, the same group that included Tyrannosaurus rex and Velociraptor. The evolution of flight within dinosaurs was a gradual process, starting with gliding and parachuting forms.
The evolutionary link is supported by numerous shared anatomical traits, including the presence of feathers, hollow bones, and a specialized wrist bone that allows the folding of the wing. Fossils such as Archaeopteryx, which lived about 150 million years ago, demonstrate this transition. Archaeopteryx exhibited a mix of reptilian features, like teeth and a long bony tail, alongside fully developed flight feathers.
The ability for powered flight evolved in some feathered dinosaurs long before the emergence of modern birds. These early flying forms, like the dromaeosaurids and troodontids, were already experimenting with flight capabilities. This evolutionary success means that every bird seen today, from a hummingbird to an eagle, is a living representative of the dinosaur lineage, a classification that survived the mass extinction event at the end of the Cretaceous period.