These animals evolved from reptiles during the Mesozoic Era about 150 million years ago.
Today, more than 9,000 species inhabit virtually every terrestrial habitat on the planet.
Birds have a number of characteristics that set them apart from other vertebrates such as feathers, bills and a furculum.
Birds, best known for their ability to fly, are unmatched in their command of the skies.
Albatrosses glide over the vast open sea, hummingbirds hover motionless in mid-air, and birds of prey capture prey with pinpoint accuracy.
But not all birds are aerobatic experts. Some species such as ostriches, kiwis and penguins, lost their ability to fly long ago in favor of lifestyles suited more for land or water.
Key Characteristics of birds are –
(i).These animals are vertebrates,
(ii). These are tetra pods,
(iii). These are endothermic,
(iv). These animals have feathers and bills,
(v). These animals have lightweight bones (bones that are either hollow or spongy),
(vi).These animals have fused bones in pelvis, feet, hands, and head, (vii). No teeth or maxillary bones of the jaw (reduces anterior weight), (viii). These animals have Four-chambered heart and high metabolic rates,
(ix). Produce large, richly provisioned external eggs