Research has revealed that iguanas living on the remote islands of Fiji have a remarkable history, having traveled thousands of miles across the ocean on vegetation over the past 30 million years to reach their current home.

A recent study of the Iguanidae family tree, which comprises approximately 2,100 reptilian species, including marine iguanas, chameleons, and chuckwalls, has found that Fiji iguanas are closely related to lizards in the American Southwest.

Given the significant geographic distance between the two regions and their relative genetic proximity, the research team concludes that a group of desert reptiles must have hitched a ride on floating debris in the ancient past, eventually making it to Fiji and surviving there for around 34 million years. The team’s findings were published in the Proceedings of the National Academy of Sciences.

According to Simon Scarpetta, a herpetologist and paleontologist at the University of San Francisco and lead author of the paper, “The lineage of Fiji iguanas split from their sister lineage relatively recently, around 30 million years ago, which coincides with volcanic activity that could have produced land.” Scarpetta added that the probable mechanism of dispersal was rafting on a vegetation mat, providing the iguanas with food during their journey across the Pacific.

Scarpetta also noted that the iguanas were likely resilient to the conditions they faced, including lack of standing water and high temperatures. The timeline for this trans-Pacific journey is estimated to be between 2.5 to 4 months, according to recent simulations.

If the team’s conclusions are correct, the ancestors of Fiji iguanas traveled an impressive 5,000 miles from western North America to Fiji, riding on vegetative flotsam and ocean currents. This journey would be the longest-known transoceanic dispersal of a terrestrial vertebrate, showcasing the incredible adaptability of these creatures.

Scarpetta explained that iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, making them well-suited for such a journey. “If any group of vertebrate or lizard could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one,” Scarpetta said.

A genetic analysis of over 4,000 iguana genes from more than 200 specimens revealed that the Fiji iguana’s closest relatives are the North American desert iguanas. The researchers believe that the lizards arrived on the island within the last 30-odd-million years, given the timing of the Fiji iguanas’ genetic divergence from the North American desert iguanas.

Co-author Jimmy McGuire, a herpetologist at UC Berkeley, noted that while it seems unlikely that iguanas reached Fiji directly from North America, alternative models involving colonization from adjacent land areas do not fit the time frame. “That they reached Fiji directly from North America seems crazy,” McGuire said, “but alternative models involving colonization from adjacent land areas don’t really work for the time frame, since we know that they arrived in Fiji within the last 34 million years or so.”

The idea that iguanas floated to the islands of the South Pacific has been previously suggested, but the new research rules out a South American origin for the Pacific iguanas and the notion that the reptiles evolved from an older lineage that was widespread in the Pacific before going extinct.

Scarpetta added that one question worth exploring is whether iguanas hopped across islands in the Pacific from North America to Fiji, rather than rafting in a single event. However, this possibility is difficult to test, and no fossils of Fijian iguanas are known from anywhere in the Pacific besides Fiji and Tonga.

Despite being isolated on remote islands, the four species of iguana on Fiji and Tonga are endangered due to habitat loss, predation, and the exotic pet trade. The new research highlights the remarkable history of these creatures and emphasizes the importance of conservation efforts to protect them.