The origin of the ratites, large flightless birds from the Southern Hemisphere, along with their flighted sister taxa, the South American tinamous, is central to understanding the role of plate tectonics in the distributions of modern birds and mammals. Defining the dates of ratite divergences is also critical for determining the age of modern avian orders. To resolve the ratite phylogeny and provide biogeographical data to examine these issues, we have here determined the first complete mitochondrial genome sequences of any extinct taxa--two New Zealand moa genera--along with a 1,000-base-pair sequence from an extinct Madagascan elephant-bird. For comparative data, we also generated 12 kilobases of contiguous sequence from the kiwi, cassowary, emu and two tinamou genera. This large dataset allows statistically precise estimates of molecular divergence dates and these support a Late Cretaceous vicariant speciation of ratite taxa, followed by the subsequent dispersal of the kiwi to New Zealand. This first molecular view of the break-up of Gondwana provides a new temporal framework for speciation events within other Gondwanan biota and can be used to evaluate competing biogeographical hypotheses.