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Although designating the Night Parrot (Geopsittacus occidentalis) and the Ground Parrot (Pezoporus wallicus) as each other's closest taxonomic relatives is generally accepted, placing this group with respect to other Australo-Pacific parrots has proven problematical. To examine the phylogenetic relationships of these two species, a 924-bp fragment of the cytochrome-b gene was sequenced from single representatives of the following genera: Geopsittacus, Pezoporus, Neophema, Melopsittacus, Platycercus, Polytelis, Strigops, and Calyptorhynchus. Maximum-parsimony, maximum-likelihood, and distance trees all supported a close association between Geopsittacus and Pezoporus. These two genera were also found to be closely linked with Neophema and Melopsittacus. Despite superficial morphological similarities, Geopsittacus and Strigops (Kakapo) were found not to be closely related.
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Christidis et al. (1994) studied this question.
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