The Development of Flight

Humans have always been fascinated with flight, as we can see by the Greek stories of Icarus and Daedalus. Humans have been able to achieve flight in relatively recent years, but other animals have been doing it for millions of years.

Four groups of animals have developed the ability to fly, each using a different technique than the other three. The first group to attain flight were the insects, possibly as long ago as 345 million years, during the Carboniferous Period of the Palaeozoic Era. Some insects grew to gigantic proportions in the Carboniferous, such as a dragonfly-like species that had a wing span of 70 cm (28 inches).

The first vertebrates (animals with backbones) to fly were the Pterosaurs (see my article, "Pterosaurs: The First Flyers"), who lived from the Triassic Period through the Cretaceous Period. The Pterosaurs had membraneous wings, similar to bats, that were supported by elongated fourth metacarpals (fingers).

The Pterosaurs are often portrayed as only able to glide, but even the earliest Pterosaurs have well developed sternums (the site of attachment of the pectoralis muscle, the primary muscle responsible for the power stroke during flight), so at least some Pterosaurs must have been good flyers.

The next group to attain flight were the birds, the first of which was Archaeopteryx (see my article, "Archaeopteryx: The Ancient Wing"). Archaeopteryx lived during the Jurassic Period, but some paleontologists believe that it might not have been capable of true flight, because it lacked a large sternum or keel to attach its wing muscles to. So, it is possible that birds may not have attained true flight until the Cretaceous Period.

Birds have modified their upper limbs to have an elongated second metacarpal, and have feathers to cover and shape their wings. The shape of a bird's wing is very important to its ability to fly.

Fossils of Archaeopteryx found in the lithographic limestone of Solenhofen, Germany show that this early bird had feathers, but some scientists believe that the feathers may have only been for insulation, and that their use in flight arose much later with the Cretaceous birds. Feathers come from the same body tissue as scales, and some paleontologists believe that some species of dinosaurs might have also had feathers to keep them warm. We have a few preserved samples of dinosaur skin that show that those particular species of dinosaur did not have feathers, but this does not mean that other species could not have had feathers. This is a mystery still to be solved!

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