About 9,000 different species of birds exist today in our world. They come in all sizes, forms, and colours. There are brightly coloured parrots and macaws in tropical America, and large cassowaries and emus that cannot fly in Australia. Tiny warblers and sparrows are found in temperate America, and ducks, bustards and cranes in India. Gulls and vultures soar through the skies the world over. Plump chickens and turkeys are found in farmyards everywhere.
There are two main bird groups- paleaeognathae and neognathae. The paleaeognathae, includes birds that first evolved during the Cenozoic Era, after the dinosaurs became extinct-mostly ratites such as ostriches, emus and kiwis. The neognathae can trace their roots much farther back into the Mesozoic Era, and includes all other types of birds.
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