The ancestors of birds were clearly reptiles – birds still have scaly legs, and they lay hard-shelled eggs. In fact, it is now known that birds are actually the living descendants of the dinosaurs.
Like the dinosaurs, early birds had teeth, fingers and a long, bony tail, but they also had small wings and a few feathers. They may have used their wings to glide from tree to tree, or to give them extra speed when escaping from predators on the ground. Gradually, their body structures developed so that they could lift themselves into the air and fly.
Archaeopteryx emerged in the late Jurassic Period, about 150 million years ago. Following Archaeopteryx came small flying birds such as Sinornis, which had shorter, more bird-like tails than Archaeopteryx. Up until the end of the Cretaceous Period, 65 million years ago, most birds still had teeth. These were useful for feeding on fish and insects, their main prey. Ichthyornis and Hesperornis were among the first marine birds and fed on fish, swooping over the waves like gulls or diving from rocks.
At the end of the Cretaceous Period, the dinosaurs, along with many other reptiles died out, but many birds and mammals survived. A wide variety of different kinds of birds appeared, and by Eocene times, 50 million years ago, all the bird groups we know today had emerged.
After the dinosaurs died out, some birds became large predators. Some kinds stood almost three metres tall. They were flightless, their small wings acting only to balance their heavy bodies. Ferocious meat-eaters, such as Andalgalornis and Diatryma, probably crushed mammals such as small, early horses in their powerful jaws. Other birds, such as Argentavis, a vulture with a seven-metre wingspan, were scavengers.
Some kinds of birds have become extinct quite recently, due to the arrival of humans into their habitats. They were hunted for food, or preyed upon by rats, cats and dogs which the humans brought with them. Two groups of large, flightless birds, the elephant birds of Madagascar and the moas of New Zealand, were completely wiped out within just a few hundred years.
Picture Credit : Google