Described by French naturalist Anselme Gaëtan Desmarest in 1826, the genus Calyptorhynchus has five species. They are all mostly black in colour, and the taxa may be differentiated partly by size and partly by small areas of red, grey and yellow plumage especially in the tail feathers. It is the sole genus of the "dark cockatoo" subfamily Calyptorhynchinae. Studies based on the mitochondrial DNA 12S gene fragment suggested that other sexually dichromatic species, the gang-gang cockatoo as well as the cockatiel may be the closest living relatives of Calyptorhynchus (Brown & Toft, 1999). However, subsequent studies, including more genes confirm the morphological taxonomy with the gang-gang cockatoo most closely related to the Galah, within the white cockatoo group, and with the cockatiel as