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The order Psittaciformes includes about 342 species of bird which are generally grouped into two families: the Cacatuidae or cockatoos, and the Psittacidae, the parrots. The term parrot can be used to indicate either the Psittacidae alone or the entire order. All members of the order have a characteristic curved beak shape and zygodactyl feet (two toes face forward and two back).
Some authorities regard the lorikeets as a third family rather than part of the Psittacidae, or lump the cockatoos into one giant family. 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.
Birds of the parrot families can be found in most of the warmer parts of the world, including India, South East Asia and West Africa, with one species, now extinct, in the United States (the Carolina Parakeet). By far the greatest number of Psittaciforme species, however, come from Australasia, South America and Central America.
Origins
In general, an area which has, relative to other areas, a great concentration of different species within a particular family is likely to be the original ancestral home of that family. The diversity of Psittaciformes in South America and Australasia suggests that the order has a Gondwanian origin. The parrot family's fossil record, however, is sparse and their origin remains a matter of informed speculation rather than fact.
The earliest known record of parrot-like birds dates to the late Cretaceous about 70 million years ago. A single 15 mm fragment from a lower bill found in Wyoming is similar to that of a modern lorikeet. It is not clear if this find should be classified as a parrot or not.
Europe is the site of more extensive records from the Eocene (58 to 36 million years ago). Several fairly complete skeletons of parrot-like birds have been found in England and Germany. Some uncertainty remains, but on the whole it seems more likely that these are not true ancestors of the modern parrots, but are a related group which evolved in the Northern Hemisphere but have since died out.
The Southern Hemisphere does not have nearly as rich a fossil record for the period of interest as the Northern, and contains no known parrot-like remains earlier than the early to middle Miocene, around 20 million year ago. 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 .
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