The genus Brachylophus consists of three extant iguanid species native to the islands of Fiji and a giant extinct species from Tonga in the South Pacific. One of the extant species, B. fasciatus, is also present on Tonga, where it has apparently been introduced by man.
Brachylophus species are the most geographically isolated iguanas in the world. Their closest extant relatives are present in primarily tropical regions of the Americas and islands in the Galápagos and Lesser and Greater Antilles. Several of these genera are adapted to xeric biomes. The location of members of Brachylophus, so distant from all other known extant or extinct iguanids, has long presented a biogeographical puzzle.
These iguanas have been hypothesized to have evolved from New World iguanas that rafted 8000 km west across the Pacific Ocean with the aid of the South Equatorial Current. While a rafting voyage of four months or more might seem implausible, the ancestors of Brachylophus may have been preadapted for such a journey by having water requirements that can be satisfied by food alone, as well as comparatively long egg incubation periods.
Source: en.wikipedia.org/wiki/Brachylophus - 2011.2008