Get to know the world's only ocean-going lizard

Order: Squamata

Family: Iguanidae

Genus: Amblyrhynchus

Species: A. cristatus

Range: Endemic to Ecuador’s Galápagos Islands—Isabela, Fernandina, Española, Floreana, Santa Cruz & other islets; in coastal regions along the islands’ rocky shorelines

Population: Unknown but estimated at 200,000-300,000

How to spot them: Spiky dorsal scales; short, blunt snout; sooty black with mottled patches of gray, brown, or buff (except on the southern islands of Española and Floreana, where breeding males acquire “Christmas” coloration of bright red splotches with green and sometimes blue legs); about 2.5 feet in length on average—big males can reach 5 feet.

IUCN Red List Status: Vulnerable: At high risk of extinction in the wild

Marine iguanas munch, swim, sneeze, and lounge on Fernandina Island.

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Marine iguanas have taken their share of verbal barbs. Even Charles Darwin described them in his journal as “disgusting, clumsy lizards” and said someone else referred to them as “imps of darkness.” But despite their frightening demeanor these docile herbivores pose no threat. In fact, like most wildlife in Galápagos, they nonchalantly go about their business—unfazed by humans passing among them.

As their name suggests marine iguanas have a unique claim to fame—they’re the world’s only swimming lizards! Foraging for algae and seaweed, larger animals dive down to 50 feet and feed for up to 20 minutes; smaller individuals feed on the exposed intertidal region. An array of unique adaptations helps them survive—from a flattened tail, adapted for swimming, to long claws that grip tightly to the sea floor in wave-washed tidal areas. A blunt face and unique jaw and tooth structure are also well adapted to scraping plant life off the rocks.

But one of their most interesting adaptations is their ability to conserve energy and heat by dropping their heart rate and metabolism in half when submerged for periods of time. After a dip in the chilly ocean, marine iguanas can lose up to 50°F of body heat. That’s why on land you’ll frequently find them lounging in the sun, soaking up rays to warm up before their next dive. They often live in large colonies, where it’s common to see them piled on top of one another—another smart trick for conserving heat.

Learn more facts about this surprising swimmer.

Salty Sneezers

Marine iguanas ingest large quantities of saltwater along with the algae they eat. To prevent dehydration, special glands near their nose filter it out of the blood, then they ‘sneeze’ to expel the excess salt. This frequent and funny habit often leaves their heads and snouts encrusted with white salty crystals.

Shrinky Dinks

When food is scarce—particularly during El Niño events—these lizards have the incredible ability to shrink by as much as 20 percent, in both length and overall size. Smaller bodies require less food, of course, but once their preferred menu of algae returns to high levels, they soon regain the lost size. 

No Place Like Home

These iguanas are endemic—found only in the Galápagos. Scientists theorize that land-dwelling iguanas from South America drifted out to sea on logs or other debris, eventually landing in the islands. The marine species likely emerged from those early settlers and then spread throughout the archipelago, uniquely adapting to life in the incredibly remote region.

Sound the Alarm

The non-vocal marine iguana has a unique ally in the mockingbird, who uses an alarm call to warn their fellow feathered friends when the predatory Galápagos hawk is near. Iguanas have evolved to recognize and respond to this call by scrambling to safety.