Convergence and divergence in the evolution of aquatic birds

Aquatic birds exceed other terrestrial vertebrates in the diversity of thei r adaptations to aquatic niches. For many species this has created difficul ty in understanding their evolutionary origin and, in particular, for the f lamingos, hamerkop, shoebill and pelecaniforms. Here, new evidence from nuc lear and mitochondrial DNA sequences and DNA-DNA hybridization data indicat es extensive morphological convergence and divergence in aquatic birds. Amo ng the unexpected findings is a grouping of flamingos and grebes, species w hich otherwise show no resemblance. These results suggest that the traditio nal characters used to unite certain aquatic groups, such as totipalmate fe et, root-propelled diving and long legs, evolved more than once and that or ganismal change in aquatic birds has proceeded at a raster pare than previo usly recognized.