The genus Brachylophus consists of four extant iguanid species native to the islands of Fiji and a giant extinct species from Tonga in the South West Pacific. The location of members of Brachylophus, so distant from all other known extant or extinct iguanids, has long presented a biogeographical enigma.

One hypothesis to account for this biogeographical puzzle, based in part on an estimated divergence date of 50 million years ago (although more recent studies have revised this to about 35 million years ago However, no other fossil or extant species of this putative lineage have been found to date in Southeast Asia, Australasia or the western Pacific outside of Fiji and Tonga. 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. In 2017, B. gau was described as a new species from Gau Island.

A giant Tongan species, Brachylophus gibbonsi, similar in size and build to an iguana of the genus Cyclura once existed on Lifuka, islands in the Ha‘apai group and Tongatapu but became extinct in prehistoric times due to predation by humans and their domestic animals. An even larger extinct iguana of the separate genus Lapitiguana was formerly present on Fiji.

  • (1989) A Phylogenetic Analysis and Taxonomy of Iguanian Lizards (Reptilia: Squamata). University of Kansas Museum of Natural History Miscellaneous Publications 81: 1-65. PDF fulltext
  • (2001): Total evidence, sequence alignment, evolution of Polychrotid lizards, and a reclassification of the Iguania (Squamata: Iguania). American Museum Novitates 3343: 1-38. PDF fulltext
  • Images of B. bulabula