A cockatoo is any of about 20 species of bird belonging to the familyCacatuidae. Along with the Psittacidae family ("true" parrots), they make up the order Psittaciformes (all parrots). The name cockatoo originated from the Malay language 'kakaktua' meaning 'older sister' ('kakak' - sister and 'tua' - old).
Cockatoos share many features with other parrots including the characteristic curved beak shape and a zygodactyl foot (two toes forward and two toes back). They differ however in a number of anatomical characteristics, including the often spectacular movable headcrest, and their lack of the Dyck texture feather composition which gives many parrots their iridescent colours. Cockatoo species are on average larger than other parrot species. The Cockatiel though is a small cockatoo and the very biggest parrots are not cockatoos, the Hyacinth Macaw being the longest and the Kakapo the heaviest.
Cockatoos as a family have a much more restricted range than the larger parrot group, occurring naturally only in Australia and nearby islands.
The majority view, however, is that the Cacatuidae are quite distinct, having a movable headcrest, different arrangement of the carotid arteries, a gall bladder, different skull bones, and not having the Dyck texture feather composition which, in the Psittacidae, scatters light in such a way as to produce the vibrant colours of so many parrots.
At this point, however, is found the first unambiguous parrot fossil (as opposed to a parrot-like one), an upper jaw which is indistinguishable from that of a modern white cockatoo.