The marine iguana is the only extant species of lizard that lives in a marine habitat and is classified as a marine reptile. It is endemic to the Galápagos Islands and feeds mainly on algae. 

Dives and appearance

While most females and smaller males eat algae washed free at low tide, the large males frequently forage underwater. They can dive up to 30 m (98 ft) deep, although they normally stay in shallower waters. Marine iguanas are cold-blooded animals and, like the slightly larger Galápagos land iguanas, need to warm up regularly in the sun. As they lose more heat in cold water than their relatives on land, their scales are darker. However, the color of males changes with the seasons. Marine iguanas have special glands on their nostrils through which they excrete excess salt. The resulting salt encrustations on their heads are often clearly visible.

Evolution

Scientists now assume that the marine iguana and the land iguana have a common ancestor, which probably arrived at the archipelago from the American mainland on natural rafts and then split into different species. The size and color of marine iguanas varies depending on the home island, with interbreeding also occurring, even with land iguanas. In 2014, a marine iguana was discovered on Isla de la Plata, around 20 km (12.4 mi) off the Ecuadorian coast.

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