Researchers have long wondered how iguanas got to Fiji. Most modern-day iguanas live in the Americas – thousands of miles and one giant ocean away.

They thought maybe they scurried there through Asia or Australia before volcanic activity pushed the Fijian islands so far away.

But new research suggests that millions of years ago, iguanas pulled off the 5,000 mile (8,000km) odyssey on a raft of floating vegetation – masses of uprooted trees and small plants. That journey is thought to be a record – further than any other land-dwelling vertebrate has ever travelled on the ocean.

Scientists think that’s how iguanas got to the Galápagos Islands off Ecuador and between islands in the Caribbean. Initially they thought Fiji might be a bit too far for such a trip, but in a new study, researchers inspected the genes of 14 iguana species spanning the Americas, the Caribbean and Fiji. They discovered that Fijian iguanas were most closely related to desert iguanas from North America, and that the two groups split off around 31m years ago.

The researchers created a statistical model using that information and other data on where iguanas live today and how they may spread. It suggested that the iguanas most likely floated to Fiji from North America.

“Given what we know now, their result is by far the most strongly supported,” said Kevin de Queiroz, an evolutionary biologist at the Smithsonian National Museum of Natural History, who was not involved with the new study.

The research was published on Monday in the journal Proceedings of the National Academy of Sciences.

The journey from North America to Fiji could have taken a few months, but these desert iguanas would have been ideal passengers because they were adept at resisting dehydration and could have snacked on the plants underfoot.

“If you had to pick a vertebrate to survive a long trip on a raft across an ocean, iguanas would be the one,” said study author Simon Scarpetta from the University of San Francisco, in an email.

Many Fijian iguana species are endangered, and an invasive green iguana roams the islands today, said study author Robert Fisher of the United States Geological Survey. Figuring out where these creatures came from can equip scientists with the tools to better protect them in the future.