- [Narrator] Much like today's birds,

pterosaurs ruled Earth's Mesozoic skies.

(pterosaur cawing)

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 the very first vertebrates on Earth

to take to the skies.

The most well-known pterosaur is the pterodactycl.

It was the first one discovered back in the 18th 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 40',

and likely soared through the skies,

hunting for baby dinosaurs below.

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've been relatively light for their size,

because, much like birds, their bones were hollow.

Hollow bones would've 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 11.5' tall, with a wingspan of 39',

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 every 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.