Measurements of Holocene raven bones from New Zealand show that birds from the Chatham Islands were significantly larger, on average, than those from the South Island, which were in turn significantly larger than North Island birds. Size variation on the North and South Islands appears to have been clinal in accordance with Bergmann's Rule. Three taxa are recognised: the Chatham Islands raven Corvus moriorum Forbes, 1892, the North Island raven C. antipodum antipodum (Forbes, 1893) and the South Island raven C. a. pycrafti n. subsp. A lectotype is designated for C. moriorum and a neotype for C. antipodum. New Zealand ravens were the largest crows in the Australasian region, and the Chatham Islands raven was probably the world's fourth- or fifth-largest passerine. Nothing in the shape or relative size of New Zealand raven bones suggests adaptation for anything other than the generalised crow niche, except that the tarsometatarsus is relatively long, perhaps as an adaptation to increased walking or running on the ground. New Zealand ravens were strong fliers with no reduction in flying ability compared to weak-flying New Zealand birds such as Callaeas. New Zealand ravens had a more ossified palate than C. brachyrhychos and C. corax of the Northern Hemisphere, while C. coronoides of south-east Australia seems to be intermediate in this regard. C. coronoides is the most probable closest relative of New Zealand ravens, and the latter probably developed from an invasion of New Zealand by C. coronoides or crows ancestral to it.
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