The only lizard on Earth that hunts for food beneath the ocean waves

Nature · Published 3 October 2026 Swipe more like this →

In short: Charles Darwin famously called them hideous and clumsy, yet these Galápagos reptiles possess a remarkable evolutionary secret. They are the world's only modern lizards that forage in the sea, diving into frigid waters to graze on algae. Their survival depends on a suite of bizarre, highly specialized aquatic adaptations.

Marine iguanas, or Amblyrhynchus cristatus, are an evolutionary anomaly. While their ancestors likely drifted from South America on debris millions of years ago, these creatures evolved to exploit a niche no other lizard occupies. Scientists estimate the divergence between marine and land iguanas occurred roughly 4.5 million years ago, aligning with the emergence of the oldest extant Galápagos islands. Despite this deep evolutionary split, the two species remain mutually fertile, occasionally producing rare, infertile hybrids where their territories overlap.

To thrive in the marine environment, the iguana has undergone significant physiological changes. Their blunt snouts and razor-sharp teeth are perfectly shaped for scraping algae from submerged rocks, while their laterally flattened tails provide the propulsion needed to navigate heavy currents. Because they ingest vast amounts of salt while feeding, they have developed specialized glands to cleanse their blood. Their dark gray skin serves a vital thermal purpose, allowing them to absorb sunlight rapidly to warm their bodies after returning from the cold ocean.

The species is highly diverse, with populations across the archipelago exhibiting unique sizes, shapes, and colors. Taxonomic reviews, including a major 2017 study, have identified numerous subspecies, some named for their distinct island homes and others, like A. c. godzilla, for their imposing nature. Despite their resilience, they remain vulnerable. They face constant threats from non-native predators like rats and feral cats, as well as environmental pressures from El Niño cycles and potential oil spills. While they are protected throughout the Galápagos, their exact population numbers remain unknown, leaving their future as a unique marine reptile a subject of ongoing concern.

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