Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 31, Number 6;   June, 2004

Landlubber Chameleons Navigated the Oceans to Spread Around the World

by Helen Pearson

Chameleons aren't good swimmers: Their mitten-like feet are made to grasp twigs and trees. Yet the intrepid animals charted the seas several times in the past 26 million years, say Chris Raxworthy and his colleagues of the American Museum of Natural History in New York. The team built up a chameleon chronicle by comparing the anatomy and genetics of 52 species worldwide. The creatures originated on the island of Madagascar off southern Africa, they found, and probably spread out of Madagascar in several waves. "It's pretty bold," says Olivier Rieppel, who studies reptile evolution at the Field Museum in Chicago, Illinois, because it seems counter-intuitive. "It's hard to imagine an animal swimming more awkwardly," he says. The lizards' most likely escape route was an upturned tree, says Rieppel, or chunks of land chewed off by waves. There are also suggestions that a land bridge once linked Madagascar and mainland Africa - in which case the reptiles might have strolled across.

Land or sea, Raxworthy's idea counters previous accounts of chameleon history: That they originated on the ancient supercontinent Gondwana and were divided when the land mass split. India and Madagascar together broke away from Africa 165 million years ago. Madagascar and the Seychelles subsequently separated from India. These events occurred long before chameleons first appeared on the planet - 26 million years ago, according to fossil record.

Many other animal and plant species are thought to have evolved when the movement of continental plates created barriers such as seas and mountains. Divided by water or crag, populations are thought to have evolved into new, related species. This type of hypothesis can be tested by marrying evolutionary trees with geological records. Dispersal hypotheses such as Raxworthy's are more difficult to check: "There's a lot more speculation," says Mark Springer at the University of California in Riverside. Springer recently showed that the earliest split in placental mammals into two basic groups coincides with the separation of South America and Africa about 100 million years ago. Researchers accept that continental movements and ocean navigation play a role in species dispersal. "They're both very important," says Springer.