Evolutionary age of the Galapagos iguanas predates the age of the present Galapagos Islands

New geological findings suggest that volcanoes existed over the Galapagos hotspot long before today's islands emerged less than 5 million years ago. The evolution of some of Galapagos' biota might have taken place on these former islands. This study investigates the evolutionary history of two of the archipelagos' older vertebrate taxa, the endemic Galapagos marine and land iguana (genera Amblyrhynchus and Conolophus). Mitochondrial rDNA sequences (in total about one kilobase of the 12S and 16S genes) were obtained from all extant genera of the family Iguanidae and the outgroup Oplurus. The phylogenetic analyses suggest that the Galapagos iguanas are sister taxa, Rate comparisons between the iguanid sequences and a corresponding set of sequences from ungulates with known fossil ages date their separation time at 10 million years, or more. The results strengthen the hypothesis that extended speciation times in the Galapagos are possible and provide an estimate of the minimum time inhabited islands of the archipelago may have existed. (C) 1997 Academic Press.