A genetic study has overturned decades of assumption about iguanas living on Clarion Island, Mexico's westernmost and oldest island in the Revillagigedo Archipelago. Researchers now believe the spiny-tailed iguanas evolved there in isolation roughly 425,000 years ago—long before humans set foot in the Americas.
For years, biologists assumed the military introduced these lizards to the island sometime between the 1970s and 1990s, when Mexico's armed forces brought pigs, sheep, and rabbits to Clarion. Wildlife records from earlier expeditions never mentioned iguanas, which seemed to confirm the theory. But when Daniel Mulcahy from Berlin's Museum of Natural History visited in 2013 and 2023 to study the island's snakes, something didn't add up.
"The iguanas looked different from mainland populations," Mulcahy suspected. Genetic testing proved him right. The island's iguanas diverged from their mainland cousins roughly 425,000 years ago—a timespan that rewrites the entire story of how they got there.
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Start Your News DetoxThe most likely explanation: spiny-tailed iguanas floated across the Pacific Ocean on vegetation mats from the Mexican mainland, about 1,100 kilometers away, and arrived on Clarion so long ago they evolved separately. Once isolated, they became what researchers now call "an evolutionarily significant unit"—potentially a distinct subspecies or even species entirely, though more data is needed to confirm.
Why had earlier visitors missed them? Clarion's dense cactus thickets and tall grasses historically hid the iguanas in rock outcrops and burrows. But when the military's livestock and a major fire in 1984 cleared much of that vegetation, the lizards finally became visible to human eyes.
This discovery carries real weight for conservation. The Mexican government, believing the iguanas were an invasive species, had been planning their eradication. The new findings change everything. "Our research demonstrates that iguanas are native to Clarion and should be considered part of the natural fauna, which should be conserved rather than eradicated," the study's authors wrote. Rayna Bell, an amphibian and reptile expert at the California Academy of Sciences, called this type of work "fundamental to conserving some of the world's most unique and imperiled diversity."
One island, one species, one genetic surprise—and suddenly a conservation plan shifts from elimination to protection.
