Two forms of a large and flightless rail (takahe) belonging to the genus Porphyrio and endemic to New Zealand have been described, although their taxonomy has been repeatedly questioned. Analyses of osteometric data from modern and Quaternary fossil material show such a degree of allometric distinctiveness that it is considered that the two forms are, indeed, different species as originally described, Porphyrio mantelli (Owen), Porphyrio hochstetteri (Meyer). It is suggested that this degree and type of difference could have resulted from the two species arising independently from similar volant ancestors.