There is considerable discussion concerning the evolution of the marine iguana and its relationship to the Galápagos land iguana, but DNA studies indicate that both are descended from the common iguana of mainland South America. In breeding season the males (especially those on Española – see Gardner Iguana for an example) are very colorfully marked with red and green blotches.

Though they appear very foreboding and dangerous, they are vegetarian, feeding on algae and other marine vegetation. Their threat displays are largely bluffs, but two males facing off may resort to butting heads until one backs down and turns away. The iguana shown here was engaged in approaching our panga bobbing its head in a threat gesture. On Fernandina another iguana approached me while I was sitting on the rocks, fiercely bobbing its head. I held my ground and the lizard turned away at about two feet (.6 m) distance.

Just as much as the giant tortoise, the marine iguana is a signature species for the Galápagos Islands and are found, often in startling numbers, on rocky coasts (preferably with southern exposure) throughout the archipelago.