Laura Erickson's For the Birds

(Recording of a Rock Dove)

The flight of birds gave people, from Leonardo da Vinci to the engineers at NASA, a vision of the future. But it has also given paleontologists a clearer vision of the past, as they come to understand that the many similarities between dinosaur skeletons and bird skeletons are no coincidence–that in all probability, one main line of dinosaurs, including Tyrannosaurus rex, continues to live today—in the form of birds.

Birds are far from the only animals capable of flight. The vast majority of insects on earth fly, and of the mammals, bats are excellent flyers, migrating long distances and eating insects on the wing much like swallows. Even reptiles used to have some flyers—the pterosaurs. These winged creatures, which lived at the time of the dinosaurs, weren’t true dinosaurs themselves, but there were true dinosaurs that also developed successful flight. Archeopteryx was the first known dinosaur clearly capable of flight. It was also the first known dinosaur to sport feathers. Prehistoric dinosaur flight and modern bird flight follow exactly the same principles, using exactly the same bones and muscles—and this flight mechanism is unique, unmatched in the animal kingdom. The unique features of dinosaur and bird flight are part of the evidence that has convinced a body of ornithologists and paleontologists that dinosaurs weren’t reptiles at all—they were, in reality, the first birds.

The most important differences between bird flight and the flight of bats and pterosaurs came from the development of feathers. Each stiff flight feather forms a separate lifting surface, which is supported at a single point, the base of the feather shaft where it joins the wing muscle along the arm bone. The entire force from the wing is transmitted to the body through the shoulder joint alone. In bats and pterosaurs, the wing membrane forms a continuous lifting surface and is supported by the wing skeleton, the side of the body, and the hind leg. That means the hind legs in bats and pterosaurs couldn’t be used for much else.

The development of feathers on birds is probably why this last group of dinosaurs never became extinct. Not only did the feathers provide insulation at a time when the world may have been growing colder, but also, by enabling a bird’s entire flight structures to be limited to the arm and shoulder bones and muscles, birds were able to retain their traditional dinosaur form of locomotion as well through their legs. Robins running on a lawn searching for earthworms move much the way that ancient dinosaurs once did. And yet robins can do one thing that Tyrannosaurus rex could not—they can get off the ground.

Most birds take advantage of both their wings and their legs for locomotion, enabling them to successfully exploit habitats that neither the flightless dinosaurs nor bats and pterosaurs ever dreamed of. Some ocean birds, like auks and puffins, use their wings to swim underwater as well as to fly in the sky. Their feet both propel them in swimming and augment their tail area in flight by spreading out on either side of the tail. Many water birds use their feet not only for walking and paddling but also as brakes when coming in for a landing—anyone who has ever watched a goose or swan drop down with its feet extended knows how effective these big webbed airbrakes are, and how utterly unlike bats and pterosaurs their landings are.

After making their way in the world for 120 million years as oversized giants, the only dinosaurs to ultimately survive were the ones to downscale and specialize as birds. Major corporations might learn something from them.

(Recording of a Rock Dove)

This is Laura Erickson, and this program has been “For the Dinosaurs.”