forbearers might have flapped their wings to increase running speed while
escaping predators, thereby obtaining flight purely by accident.
Archaeopteryxhad teeth, claws, a long bony tail, and many skeletal fea-
tures of a small dinosaur but lacked hollow bones for light weight. Its feathers
were outgrowths of scales and probably originally functioned as insulation.
Some bird species retained their teeth until the late Cretaceous roughly 70
million years ago. Claws on the forward edges of the wings might have helped
the bird climb trees, from which it could launch itself into the air.
Upon mastering the skill of flight, birds quickly radiated into all envi-
ronments. Their superior adaptability enabled them to compete successfully
with the pterosaurs, possibly leading to that reptile’s extinction. Giant flight-
less land birds appeared early in the avian fossil record.Their wide distribution
is further evidence for the existence of Pangaea since these birds would then
have had to walk from one corner of the world to another.
After being driven into the air by the dinosaurs and kept there by hunt-
ing mammals, birds found life much easier on the ground once this threat was
eliminated because they had to expend a great deal of energy to remain air-
borne. Some birds also successfully adapted to a life in the sea. Certain diving
ducks are specially equipped for “flying” underwater to catch fish. Penguins,
for example, are flightless birds that have taken to life in the water and are well
adapted to survive in the cold Antarctic.THE PTEROSAURS
During the Jurassic, reptiles achieved great success and dominated land, sea,
and air. Some 160 million years ago, when the dinosaurs were the dominant
species on the continents, remarkable fish-shaped reptiles called ichthyosaurs
reigned over the oceans.Theybelonged to a group of animals known as diap-
sids,which includes snakes, lizards, crocodiles,and dinosaurs. Ichthyosaurs
ruled the seas from the time the dinosaurs first appeared about 245 million
years ago to about 90 million years ago. The largest of these animals were
whale sized, exceeding 50 feet in length. They had enormous eyes as big
around as bowling balls. Their fossils have been found throughout the world,
suggesting they migrated extensively like modern whales.
Overhead were flying reptiles with wingspans up to 30 feet or more
called pterosaurs (Fig. 147),including the ferocious-looking pterodactyl.They
originated in the early Jurassic and appear to be the largest animals that ever
flew, dominating the skies for more than 120 million years. Pterosaurs resem-
bled both birdsand bats in their overall structure and proportions, with the
smallest species roughly the size of a sparrow. As with birds, they had hollow
bones to conserve weight for flight. The larger pterosaurs were proportionedHistorical Geology