Brigham Young University Science Bulletin, Biological Series


Iguanas, Evolution


The problem of phylogenic relationships within the iguanine phyletic line and the Madagascar iguanids have been investigated in order to explain the discontinuous distribution exhibited by the members of the family Iguanidae. Owing to inconclusive results from cytology and histological methods, the comparative morphology of the anterior osteology, myology, tongues, and hemipenes were used to determine relationships.

An examination of the above structures of the members of the iguanine phyletic lines and a comparison with the Madagascar iguanids indicates the following: ( 1 ) The Madagascar genera Chalarodon and Oplurus appear to be more closely related to each other than to other iguanid genera. (2) The Madagascar genus Oplurus is most closely related to the iguanine line of evolution. (3) Ctenosaura, Cyclura and Iguana represent the main ancestral stock of iguanines in the Western Hemisphere. (4) Cyclura is probably an early descendant of the Ctenosaura ancestral line. (5) Iguana and Ctenosaura evolved from a common ancestral stock. (6) Sauromalus is a northern derivative of the Ctenosaura ancestral line. (7) Conolophus is probably an early invader of the Galapagos Islands and is derived from the pre-Ctenosaura-Iguana iguanine ancestral stock. (8) Amblyrhynchus is a close relative of Conolophus and may be derived directly from a Conolophus ancestor. (9) Brachylophus is a derivative of the pre-Ctenosaura-Iguana ancestral stock and probably rafted to the Fiji and Tonga Islands from tropical America. (10) Dipsosaurus is more closely related to Brachylophus than any other iguanine and represents the northern extension of that generic complex. (11) The Madagascar iguanids and the Western Hemisphere iguanines were probably separated in post-Cretaceous times by continental drift which is thought to have resulted in a fracturing of Gondwanaland and the formation of Australia, southern India, Antarctica, Africa, Madagascar, and South America.