THE COMPLETE MITOCHONDRIAL GENOME OF RHEA-AMERICANA AND EARLY AVIAN DIVERGENCES

The complete mitochondrial DNA, mtDNA, molecule of the greater rhea, R hea americana, was sequenced. The size of the molecule is 16,710 nucle otides. The organization of the molecule conforms with that described for the chicken and the ostrich. It has been shown previously that rel ative to other vertebrates the NADH3 gene of the ostrich has an insert ion of one nucleotide in position 174 of the gene. The same observatio n was made in the rhea and in the newly sequenced NADH3 gene of the em u, Dromaius novaehollandiae. Comparison with the NADH3 gene of the chi cken and the rook suggests that the inserted nucleotide may be deleted by RNA editing. The divergence between the two struthioniform species , the ostrich and the rhea, was molecularly dated at approximate to 51 million years before present, MYBP. This dating is more recent than c ommonly acknowledged. Phylogenetic analysis of the complete cytochrome b genes of seven avian orders placed the Passeriformes basal in the a vian tree with the Struthioniformes among the remaining Neognathae. Th ese findings challenge the commonly accepted notion that the most basa l avian divergence is that between the Palaeognathae and Neognathae.