Ancient dna evidence reveals mexico’s clarion island iguanas are native species, not human introductions

For decades, scientists believed that spiny-tailed iguanas living on Mexico’s remote Clarion Island were brought there by humans in recent decades. New genetic research has turned this assumption on its head, revealing that these reptiles are actually ancient natives who arrived hundreds of thousands of years before humans ever set foot in the Americas.

Clarion Island, located over 700 miles off Mexico’s Pacific coast in the Revillagigedo Archipelago, has long puzzled researchers. The isolated landmass hosts several endemic species, but when military personnel introduced pigs, sheep, and rabbits in the 1970s—dramatically altering the island’s native vegetation—scientists assumed the iguanas arrived around the same time. Early scientific expeditions had failed to document the lizards, leading to speculation about their recent introduction.

However, when researcher Daniel Mulcahy from Berlin’s Museum of Natural History visited the island in 2013 and 2023 to study snakes, he noticed the local iguanas looked distinctly different from their mainland cousins. Genetic analysis proved his hunch correct: the island population split from mainland spiny-tailed iguanas approximately 425,000 years ago—roughly 400,000 years before humans reached North America.

The researchers believe these remarkable reptiles made an epic ocean journey, likely floating across 700 miles of Pacific waters on natural vegetation rafts—a rare but documented phenomenon in evolutionary biology. This discovery not only rewrites the natural history of Clarion Island but also highlights how easily scientists can mistake ancient native species for recent human introductions, especially when earlier surveys missed documenting them.