Marine iguana

The marine iguana lives on islands.

These lizards swim in the sea. They eat green plants in the water. Large males dive deep for food. Smaller ones eat near the shore. They have dark skin to stay warm. This helps them after they swim.

They have sharp claws to hold rocks. They also have spines on their backs. Females dig holes in the dirt. They lay eggs in these holes. It is a busy life in the sea!

The marine iguana lives only on the Galápagos Islands.

It is a very special lizard. It is the only lizard that spends time in the sea. These animals eat algae, which are small plants in the water.

Large males dive deep into the ocean to find food. Females and smaller males eat near the shore when the tide is low. To stay warm, they have dark skin. This dark color helps them soak up heat from the sun.

They have many useful parts for life in the water. Their tails are flat to help them swim. They have sharp claws to hold onto rocks in strong waves. They also have spines, which are pointy parts, along their backs.

Some iguanas are very colorful. Males on some islands turn bright pink or turquoise. Other iguanas stay black or grey. Females are usually dark. After mating, a female digs a hole in the soil. She lays her eggs there and leaves them to hatch alone.

The marine iguana is a truly special reptile found only on the Galápagos Islands in Ecuador.

It is the only living lizard that spends time in the ocean to find food. These animals mostly eat algae, which are tiny plants found in the sea. Because they live in such a unique way, they are very important to study. They are considered a protected species, but they still face hard jobs like El Niño cycles and oil spills.

Life in the water requires a special way of working. Large males dive deep into the ocean to reach their food. Females and smaller males stay closer to the shore to feed during low tide. To move through the waves, they use flat tails for swimming.

They also use long, sharp claws to hold onto rocks in strong currents. Their dark skin helps them soak up heat from the sun quickly. This helps them warm up after visiting the cold water.

Scientists have studied these lizards for a long time. Thomas Bell first described the marine iguana in 1825.

He gave it the scientific name Amblyrhynchus cristatus. The name comes from Greek and Latin words. Amblyrhynchus means "blunt snout," and cristatus means "crested." This refers to the low row of spines on their backs.

Even famous explorers like Charles Darwin saw them in 1835. He thought they looked very dark and clumsy on the black lava rocks.

These iguanas come in many different sizes and colors.

On the island of Genovesa, they are quite small. On Santa Cruz Island, they can grow much larger.

Some males on islands like Española are very colorful. They can show bright pinkish-red and turquoise markings.

Other iguanas stay black or grey to match the rocks. This color helps them stay warm. Large males can weigh up to 1,000 grams on Genovesa, but they can be much heavier on other islands.

Marine iguanas are closely related to land iguanas. They likely arrived on the islands by rafting from South or Central America.

Scientists think they split from land iguanas about 4.5 million years ago. Sometimes, a marine iguana and a land iguana mate to make a hybrid iguana.

These hybrids are very rare and only happen on tiny places like South Plaza. The hybrid iguanas stay on land and cannot have babies. This shows how much the two types of iguanas have changed over time.

The marine iguana, known scientifically as Amblyrhynchus cristatus, is a unique reptile found only on the Galápagos Islands of Ecuador.

While most lizards live entirely on land, the marine iguana is the only extant lizard that spends significant time in a marine environment. It has adapted to forage in the ocean for algae, which makes up almost all of its diet. Because of these specialized behaviors, it is often called a sea iguana or saltwater iguana. Although they are locally abundant, they are considered a threatened protected species. They face dangers from introduced predators, oil spills, and natural El Niño cycles.

To survive in the ocean, these iguanas use specific physical mechanisms. Large males are capable of diving deep into the sea to reach food sources. In contrast, females and smaller males typically feed in the intertidal zone during low tide. To move through the water, they use a laterally flattened tail for propulsion. They also possess long, sharp claws that allow them to grip rocks against strong ocean currents. Because the ocean water is relatively cold, the iguanas rely on their dark skin to absorb heat from the sun. This helps them quickly recover from the lethargy caused by the cold water.

Marine iguanas show significant differences between males and females, a trait called sexual dimorphism. Adult males are generally much longer and can weigh about twice as much as females. They also possess broader heads and larger bony plates, or tubercles, on their heads.

Males also have longer spines extending from their necks down to their tails. These spines and head plates can vary by island, with the most elaborate found on Fernandina Island. Females are typically darker and show much less color variation between the islands. However, on Española Island, females may adopt brighter colors when nesting to defend their sites.

Evolutionary studies help us understand how these reptiles arrived in the Galápagos. Scientists theorize that marine iguanas and Galápagos land iguanas evolved from a common ancestor. These ancestors likely arrived from Central or South America by rafting on floating debris. Recent studies using both mtDNA and nDNA suggest that the marine and land iguanas split about 4.5 million years ago. This timing aligns with the age of the oldest existing islands, such as San Cristóbal and Española.

Interestingly, the two species remain mutually fertile. On the tiny island of South Plaza, they sometimes hybridize to create a hybrid iguana. These hybrids have intermediate features, stay on land, and are infertile.

Taxonomy, the science of naming and classifying organisms, has evolved alongside our understanding of the species. Thomas Bell first described the species in 1825 as Amblyrhynchus cristatus. The genus name Amblyrhynchus combines two Greek words meaning "blunt snout." The specific name, cristatus, is Latin for "crested," referring to the spines on their backs.

While early researchers like Bell made mistakes about where the specimens came from, modern science uses genetic evidence to refine classifications. In 2017, a major review recognized several new subspecies based on morphological and genetic data. This includes subspecies like A. c. godzilla, named after the famous character, found on San Cristóbal.

Body size and color vary greatly across the different island populations. Size is often linked to the amount of available food, which depends on sea temperature and algae growth. For example, iguanas on large islands like Santa Cruz grow much larger than those on small islands like Genovesa.

On Genovesa, the subspecies nanus is among the smallest. On the other hand, the largest males can be found on Isabela and Fernandina. Coloration also changes based on the island and the season. Males on the southern islands, such as Española, can display bright pinkish-red and turquoise markings.

Other populations remain mostly black or grey to help them absorb heat more effectively.

The marine iguana's life cycle and survival are closely tied to the health of the Galápagos ecosystem. After mating, females dig holes in the soil to lay their eggs. These eggs are left to hatch on their own several months later.

While large body size is a benefit for some, it can be a disadvantage during El Niño events. During these cycles, food becomes scarce, and large males often suffer higher mortality rates than smaller ones. This makes the marine iguana a fascinating subject for studying how animals adapt to changing environments and limited resources.