Much like today’s birds, Pterosaurs ruled Earth’s Mesozoic skies, adapting to many different habitats while their dinosaur cousins roamed below.

But these were no birds… Pterosaurs were flying reptiles, and some were as big as fighter jets.

Pterosaurs means “winged lizard” in Greek, and they were very first vertebrates on Earth to take to the skies.

The most well-known Pterosaur is the Pterodactyl. It was the first one discovered, back in the 18^th century, but since then, paleontologists have uncovered more than 200 different species, including Pteranodons, which were quite large, and Quetzalcoatlus: one of the most massive Pterosaurs of all.

Named for the Aztec winged serpent god, Quetzalcoatlus had a wingspan of nearly forty feet, and likely soared through the skies hunting for baby dinosaurs below.

But not all Pterosaurs were so monstrous. Some, like Anurognathus, were the size of small birds, and probably preferred to eat insects.

With such a wide range in Pterosaur size, there is ongoing debate over how some species were able to fly. But similarities in their wing structure and anatomy may offer clues.

Pterosaur wings ran along their sides from shoulder to ankle, and each wing was held up and supported by an elongated digit. The first Pterosaur ever discovered was actually named for this characteristic: “Pterodactyl” is a combination of the Greek words for wing and finger.

Each Pterosaur wing consisted of a tough membrane laced with blood vessels, fibrous cords, and muscles.

And it has been theorized that the muscles could alter the shape of their wings in mid-flight, the same way a passenger jet might adjust its wings during takeoff and landing.

Pterosaur fossils also suggest that even the largest species must have been relatively light for their size, because much like birds their bones were hollow. Hollow bones would have enabled even Quetzalcoatlus to soar.

But not all Pterosaurs could fly. In 2009, paleontologists found an enormous specimen in Transylvania that they nicknamed “Dracula.”

At 11 and a half feet tall, with a wingspan of 39 feet, it’s one of the largest Pterosaurs ever found, but the shape of its shoulders and wings suggest it probably couldn’t get off the ground.

With ever new discovery, paleontologists are learning more about the nature of Pterosaurs.

But the hollow bones that enabled some of the largest Pterosaurs to fly, are also part of the reason their fossils are so often incomplete and the full picture of a sky once ruled by reptiles has yet to be revealed.