Life in the Air 1

The first creatures to fly were insects, but later there were flying reptiles and birds, and even later a relatively few flying mammals.

As we saw earlier, the archosaurs branched out into dinosaurs, crocodiles, birds, and also a group of flying reptiles called pterosaurs.

The pterosaurs

The pterosaurs were masters of the air until they were superseded by the birds. They came in many sizes. Some were no larger than a sparrow, others had a wing-span of 10 metres or more. Pterosaurs did not have feathered wings built as birds' wings are. Instead, pterosaurs' wings were of leathery skin fastened along the elongated fourth fingers of the animals' front claws, and anchored to their hind legs. The other front claws were short and hooked and were probably useful for crawling and for clinging.

Pterodactylus, a pterosaur

Podopteryx

A fossil found in rocks of the late Triassic in a remote area to the north of the Himalayas, gives us a clue to the way in which the pterosaurs originated. Podopteryx was a small archosaur that had taken to the trees and become a glider like the flying squirrels and flying lizards of today. The animal could presumably leap to safety when pursued by a climbing enemy and need never come to the ground in a forest. It could simply leap from tree to tree.

Podopteryx had a web of skin stretched between the fore and hind legs and another between the hind limbs and base of the tail. The latter web was the larger. However, as time went by the web of skin between the fore and hind limbs increased greatly in size.

Ancestors of the birds

The pterosaurs were not the ancestors of the birds. The two groups evolved from the archosaurs quite independently. Nevertheless, apart from their wings, skin membranes instead of feathers, pterosaurs were remarkably like birds. This is because they both had to solve the same problem: how to fly.

Scaphognathus

Hollow bones

Both birds and pterosaurs have hollow bones. In birds this serves to lighten the skeleton and form part of the efficient system of air sacs that birds use in breathing. In pterosaurs there are similar openings into the bones, which suggests they had the same kind of breathing system. Unfortunately, light bones are also very fragile, and they do not preserve well as fossils. Fossil pterosaurs and fossil birds are therefore rare.