Characteristic features of parrots include a strong, curved bill, an upright stance, strong legs, and clawed zygodactyl feet. Many parrots are vividly coloured, and some are multi-coloured. Most parrots exhibit little or no sexual dimorphism in the visual spectrum. They form the most variably sized bird order in terms of length.The most important components of most parrots' diets are seeds, nuts, fruit, buds, and other plant material. A few species sometimes eat animals and carrion, while the lories and lorikeets are specialised for feeding on floralnectar and soft fruits. Almost all parrots nest in tree hollows (or nest boxes in captivity), and lay white eggs from which hatch altricial (helpless) young.
Fossil dentary specimen UCMP 143274 restored as a parrot (left) or an oviraptorosaur
Psittaciform diversity in South America and Australasia suggests that the order may have evolved in Gondwana, centred in Australasia. The scarcity of parrots in the fossil record, however, presents difficulties in confirming the hypothesis, and there is currently a higher amount of fossil remains from the northern hemisphere in the early Cenozoic. Molecular studies suggest that parrots evolved approximately 59 million years ago (Mya) (range 66–51 Mya) in Gondwana. The three major clades of Neotropical parrots originated about 50 Mya (range 57–41 Mya).
A single 15 mm (0.6 in) fragment from a large lower bill (UCMP 143274), found in deposits from the Lance Creek Formation in Niobrara County, Wyoming, had been thought to be the oldest parrot fossil and is presumed to have originated from the Late Cretaceous period, which makes it about 70 million years old. However, other studies suggest that this fossil is not from a bird, but from a caenagnathidoviraptorosaur (a non-aviandinosaur with a birdlike beak), as several details of the fossil used to support its identity as a parrot are not actually exclusive to parrots, and it is dissimilar to the earliest-known unequivocal parrot fossils. Likewise, the earliest parrots did not have the specialised crushing bills of modern species.
Europe is the origin of the first undeniable parrot fossils, which date from about 50 Mya. The climate there and then was tropical, consistent with the Paleocene-Eocene thermal maximum. Initially, a neoavian named Mopsitta tanta, uncovered in Denmark's Early EoceneFur Formation and dated to 54 Mya, was assigned to the Psittaciformes; it was described from a single humerus.
However, the rather nondescript bone is not unequivocally psittaciform, and more recently it was pointed out that it may rather belong to a newly discovered ibis of the genus Rhynchaeites, whose fossil legs were found in the same deposits.
Fossils assignable to Psittaciformes (though not yet the present-day parrots) date from slightly later in the Eocene, starting around 50 Mya. 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 direct ancestors of the modern parrots, but related lineages that evolved in the Northern Hemisphere and have since died out. These are probably not "missing links" between ancestral and modern parrots, but rather psittaciform lineages that evolved parallel to true parrots and cockatoos and had their own peculiar autapomorphies:
The earliest records of modern parrots date to about 23–20 Mya. The fossil record—mainly from Europe—consists of bones clearly recognisable as belonging to parrots of modern type. 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 Mya. At this point, however, is found the first unambiguous parrot fossil (as opposed to a parrot-like one), an upper jaw that is indistinguishable from that of modern cockatoos.
Phylogenetic relationship between the three parrot superfamilies
The Psittaciformes comprise three main lineages: Strigopoidea, Psittacoidea and Cacatuoidea. The Strigopoidea were considered part of the Psittacoidea, but recent studies place this group of New Zealand species at the base of the parrot tree next to the remaining members of the Psittacoidea, as well as all members of the Cacatuoidea. The Cacatuoidea are quite distinct, having a movable head crest, a different arrangement of the carotid arteries, a gall bladder, differences in the skull bones, and lack the Dyck texture feathers that—in the Psittacidae—scatter light to produce the vibrant colours of so many parrots. Colourful feathers with high levels of psittacofulvin resist the feather-degrading bacteriumBacillus licheniformis better than white ones.Lorikeets were previously regarded as a third family, Loriidae,:45 but are now considered a tribe (Loriini) within the subfamily Lorinae, family Psittaculidae. The two other tribes in the subfamily are the closely related fig parrots (two genera in the tribe Cyclopsittini) and budgerigar (tribe Melopsittacini).