A rare and endangered species of iguana, Brachylophus vitiensis, was discovered resting on a piece of bark on Viti Levu island in Fiji. This remarkable sighting was captured by Don Mammoser/Alamy Stock Photo/FILE. Stay informed about the wonders of science by signing up for CNN’s Wonder Theory newsletter, offering news on exciting discoveries and scientific progress.
Around 34 million years ago, the ancestors of today’s iguanas embarked on an unprecedented overwater journey believed to be the longest undertaken by a nonhuman, land-dwelling vertebrate species. Originating from the western coast of North America, these iguanas voyaged nearly 5,000 miles (8,000 kilometers) across the Pacific Ocean, eventually reaching Fiji, according to a recent study. Evidence suggests that these iguanas accomplished this epic journey by rafting on floating vegetation, such as uprooted trees or plants.
For years, the question of how iguanas arrived in Fiji has perplexed scientists. Previous theories suggested that an extinct species of iguana traveled from the Americas without a clear timeline, while others proposed overland migration from Asia or Australia. The findings of the study, led by Dr. Simon Scarpetta of the University of San Francisco, shed light on this longstanding mystery, offering insights into how these reptiles reached such remote islands.
The research, published in the Proceedings of the National Academy of Sciences, aimed to investigate various theories, including overwater rafting and overland migration, as well as dispersal through Antarctica or the Bering land bridge. Understanding this form of water dispersal could provide valuable knowledge on how species colonized isolated regions over time.
By analyzing the genetic makeup of 14 iguana species, researchers determined that the closest living relative of Fijian iguanas is the Dipsosaurus, a desert iguana native to the southwestern United States and northwestern Mexico. Fossil evidence also supports the hypothesis that these iguanas originated in North America, with no desert iguana fossils found elsewhere in the world.
The study suggests that Fijian iguanas diverged from their American ancestors around 34 to 30 million years ago, coinciding with the volcanic formation of the Fijian archipelago. This challenges previous theories of a complex overland journey from South America.
According to a study co-authored by Dr. Jimmy McGuire, a professor of integrative biology at the University of California, Berkeley, iguanas may have reached the Pacific Islands via Antarctica, a journey that would have occurred much later in history. Dr. Shane Campbell-Staton, an associate professor of ecology and evolutionary biology at Princeton University, who was not involved in the study, noted the uncertainties in predicting divergence events between species but praised the thorough approach of the authors in collecting diverse genetic data and using multiple models to test their hypothesis.
The possibility of such a trek for iguanas is explained by their resilience to extreme conditions. With their ability to endure heat, starvation, and dehydration, iguanas, especially those in desert environments, are well-suited for long overwater voyages. Their ectothermic nature allows them to conserve energy by not needing to maintain elevated body temperatures like endothermic animals do.
While earlier estimates suggested a journey from North America to Fiji could take up to 12 months, newer simulations indicate it may have been shorter, around 2 ½ to four months. Despite challenges, such as food scarcity, iguanas could potentially rely on floating vegetation mats for sustenance during the journey. By studying dispersal events like this, scientists aim to understand which species can survive long-distance overwater travel and gain insights into how animals have spread across the globe.
Dr. Campbell-Staton emphasized the importance of recognizing overwater dispersal as a significant factor in shaping species diversity on islands worldwide. To access more news and newsletters from CNN, you can create an account on CNN.com.
