Ancient iguanas sailed around 5,000 miles from North America to Fiji by clinging to floating vegetation, new research suggests.
Around 34 million years ago, iguanas made what is believed to be the longest-known transoceanic journey of any land species, traveling nearly one-fifth of the way around the globe from North America to Fiji, according to a new study.
Scientists suggest that these ancient iguanas completed the over 5,000-mile (8,000-kilometer) voyage by rafting on mats of vegetation, likely torn from shorelines by powerful storms. “You could imagine some kind of cyclone knocking over trees where there were a bunch of iguanas and maybe their eggs, and then they caught the ocean currents and rafted over,” explained Simon Scarpetta, lead author of the study and assistant professor of environmental science at the University of San Francisco.
Fiji’s famous bright-green iguanas are the only iguanas found outside the Western Hemisphere, leaving biologists puzzled for years about how they reached such a remote part of the world. Now, a fresh genetic analysis, published March 17 in PNAS, reveals that Fiji’s iguanas are much more closely related to iguanas from the Western Hemisphere than previously thought — specifically, to species found in North America.
“The idea that they reached Fiji directly from North America seems crazy,” said co-author Jimmy McGuire, professor of biology at the University of California, Berkeley. “But other models, like coming from nearby landmasses, don’t fit the time frame since we know they arrived in Fiji within the last 34 million years or so.”
Previously, some experts theorized that Fijian iguanas — belonging to the genus Brachylophus — might have descended from now-extinct iguanas that once lived throughout the Pacific, or that they arrived via shorter routes from South America or Antarctica. But older genetic studies lacked the detail to fully resolve the mystery.
Scarpetta’s team analyzed genome-wide DNA data from over 200 iguana specimens housed in museums worldwide. Their results show that Brachylophus iguanas from Fiji are most closely related to Dipsosaurus, a genus of desert iguanas common in the hot deserts of North America. Given that desert iguanas are highly resistant to starvation and dehydration, researchers believe these traits may have enabled an ancient ancestor to survive the epic sea voyage.
“Iguanas, especially desert iguanas, can endure extreme conditions, so if any lizard could make an 8,000-kilometer journey across the Pacific on a floating mass of vegetation, a desert iguana-like ancestor would be the one,” Scarpetta noted.
The study also suggests that the arrival of iguanas in Fiji happened shortly after the islands themselves formed, with the evolutionary split between Fijian iguanas and their North American relatives occurring about 34 million years ago — aligning perfectly with geological records.
“This suggests that as soon as land appeared where Fiji now stands, these iguanas may have colonized it. No matter the exact timing, the fact that it happened is spectacular,” Scarpetta concluded.