Ostrich legs, eggs and phylogenies

The location of the region in which didactyl ratites (ostriches) evolved has been the subject of debate for the past two decades.(1-6) Paucity of the fossil record is partly responsible for the fact that a clear-cut solution to their origin has yet to be proposed. The Old World ratite fossil record consists almost exclusively of eggs and leg bones, each of which has been the basis for reconstructing evolutionary scenarios. Given the difficulties of determining which egg types corresponded to which skeletal types and the spotty nature of the fossil record, the uncertainties experienced by researchers are understandable. As a result, two main hypotheses of ostrich origins have been proposed: 1) that ostriches evolved in Eurasia and then spread to Africa,(1,4-7) and 2) that ostriches evolved in Africa and then spread to Eurasia.(2) New discoveries in Namibia indicate that the second set of hypotheses is likely to be correct, and furthermore indicate that at least two lineages of ostriches spread to Eurasia from Africa, one during the middle Miocene, the other during the upper Miocene.