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Abstract
The evolution of the ratite birds has been widely attributed to vicariant speciation, driven by the Cretaceous breakup of the supercontinent Gondwana. The early isolation of Africa and Madagascar implies that the ostrich and extinct Madagascan elephant birds (Aepyornithidae) should be the oldest ratite lineages. We sequenced the mitochondrial genomes of two elephant birds and performed phylogenetic analyses, which revealed that these birds are the closest relatives of the New Zealand kiwi and are distant from the basal ratite lineage of ostriches. This unexpected result strongly contradicts continental vicariance and instead supports flighted dispersal in all major ratite lineages. We suggest that convergence toward gigantism and flightlessness was facilitated by early Tertiary expansion into the diurnal herbivory niche after the extinction of the dinosaurs.
Ruffling ancient ratite feathers
Biologists have often pointed to the breakup of the supercontinent Gondwana to explain how related species ended up on far-flung continents, but as new research shows, that explanation doesn't fly with ratite birds. Ratite birds are a lineage of large, mostly flightless birds including the African ostrich, the Australian emu, the South American rhea, the diminutive New Zealand kiwi, and the extinct Madagascar elephant bird. Mitchell et al. examined the phylogeny of these birds, adding ancient mitochondrial DNA sequences from the extinct elephant bird. It seems that ratites originated from flighted ancestors who evolved large sizes and loss of flight only after flying to their new homes.
Science, this issue p. 898.
