Ostrich ancestors found in the Northern Hemisphere suggest new hypothesis of ratite origins.

Modern ratites (ostriches, rheas, cassowaries, emus, and kiwis) are flightless birds which have a palatal structure termed 'palaeog-nathous'1 and are found on daughter-landmasses of the Mesozoic supercontinent Gondwanaland. It has been suggested2-4 that a single flightless ancestor, widely distributed in Gondwanaland, gave rise to the various lineages of ratite birds. The temporal calibration of the DNA molecular clock is primarily based on the divergence of ratites, and depends on the validity of this hypothesis. Newly studied fossils suggest that the ancestors of ostriches are instead among a group of North American and European birds, the 'Lithornis-cohort', that had the potential of flight and from which the kiwis may have arisen separately.