Most species of birds of paradise (Paradisaeidae) are endemic in the rainforests of New Guinea. There are also a few species in the northern Moluccas and in northern Australia. Bowerbirds (Ptilonorhynchidae) are centred in New Guinea but are more widespread in Australia. The two families have often been regarded as sister groups, but in recent studies Paradisaeidae appear as sister to Corvidae, a worldwide family which is notably depauperate in New Guinea and Australia. This indicates vicariance of a worldwide ancestor, rather than invasion of New Guinea. Other families in the superfamily Corvoidea include Ptilonorhynchidae (basal), Campephagidae (Africa to New Guinea and Fiji), and Cracticidae (Australia to New Guinea). Biodiversity levels in Paradisaeidae and Ptilonorhynchidae were assessed from literature records by counting numbers of species in grid cells 1° latitude by 1° longitude. Birds of paradise are equally diverse in the Mendi square and the Mount Hagen–Wahgi Valley–Jimi Valley square. Bowerbirds are most diverse in the Mount Hagen–Wahgi Valley–Jimi Valley square. This area lies on one of the main tectonic boundaries in New Guinea, the former margin of the Australian craton, and is geologically distinctive in having several diverse accreted terranes juxtaposed there, including an ophiolite complex. It also includes the western slopes of Mount Wilhelm, one of the highest mountains in the New Guinea orogen. Paradisaeidae have secondary centres of diversity in the southern part of the New Guinea orogen (south of the former craton margin), while Ptilonorhynchidae have secondary centres north of the craton margin on the accreted terranes, and also in eastern Australia. Within New Guinea the two distributions correlate closely with the geological interpretation of the orogen as comprising southern (craton) and northern (accreted terrane) components. Within Australia, Paradisaeidae have two species per degree square in northern Cape York Peninsula (on the old Australian craton), and only one elsewhere in eastern Australia, whereas Ptilonorhynchidae have a clear Australian massing further south in Queensland, on the accreted terranes of the Tasman orogen.