LEILA FADEL, HOST:
Here's a reptilian mystery millions of years in the making. How did land-loving iguanas normally found in the Americas wind up thousands of miles away in the South Pacific in Fiji? NPR's Jonathan Lambert has more on some possible answers.
JONATHAN LAMBERT, BYLINE: Scientists have two major theories to explain how iguanas ended up on the tropical island Fiji. Simon Scarpetta is a biologist at the University of San Francisco.
SIMON SCARPETTA: People had suggested that they must have taken some kind of raft of down vegetation from somewhere in the Americas all the way across the Pacific, you know, through the doldrums of the equator, through the southern equatorial current, and then made their way to Fiji.
LAMBERT: The other idea is that Fiji and Iguanas got there much more gradually. Over many generations, iguanas from the Americas might have walked or island-hopped over land bridges that are now underwater. But biologists haven't had enough evidence to distinguish between these possibilities.
SCARPETTA: We didn't really know how the Fijian iguanas were related to other iguanas, and then we also didn't really know how old they were.
LAMBERT: To figure that out, Scarpetta and his colleagues used genomic data to build a detailed family tree. The results published in the journal PNAS surprised him.
SCARPETTA: The iguanas that live on Fiji were most closely related to a group of iguanas that I knew very well from the United States called desert iguanas.
LAMBERT: Scarpetta estimates that these iguanas split a little over 30 million years ago, a timeline that doesn't quite line up with the land bridge idea. Instead, he thinks a small group of iguanas made one single trip from North America to Fiji. Similar albeit shorter trips have been observed on tangles of downed trees in the Caribbean.
SCARPETTA: People saw in real time that green iguanas were able to get around 300 kilometers just floating on displaced vegetation from one island to the other, and so that was super cool.
LAMBERT: Reaching Fiji would have been nearly 30 times as far, but if any creature could survive, it's iguanas.
SCARPETTA: They're herbivorous, and so if they're floating around on vegetation, they may even have a source of food to eat.
LAMBERT: And with desert origins, these iguanas could have survived dehydration in the intense equatorial sun as they slowly drifted towards their new home.
Jonathan Lambert, NPR News.
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