CHICAGOAll of Madagascar's living Carnivora (an order of mammals that includes dogs, cats, bears, hyenas and their relatives) descended from a single species that dispersed from Africa to Madagascar, apparently floating across the ocean barrier aboard wayward vegetation about 24 million to 18 million years ago. Previously, scientists believed that Madagascar's seven living species of native Carnivora represented two to four separate lineages, which would have implied that these animals colonized the island independently several times.

The surprising findings will be published in Nature Feb. 13, 2003.

"Our research shows that all the species of Madagascar's Carnivora together represent a unique evolutionary branch formed by a significant, one-time event," says co-author John Flynn, MacArthur Curator of fossil mammals at The Field Museum in Chicago. "In fact, all 100 or so known species of terrestrial mammals native to Madagascar, which fall into four orders carnivorans, lemurs, tenrecs and rodents can now be explained by only four colonization events."

How and when mammals first populated Madagascar has long remained a mystery due to the lack of fossil evidence from the island, which lies about 240 miles off the east coast of Africa. To overcome this problem, the researchers analyzed genes of Madagascar's living species of Carnivora and some of their closest relatives in Africa and Asia.

Specifically, they sequenced the DNA of four genes from 20 different mammals and analyzed the resulting patterns for evidence of which carnivorans are the most closely related, evolutionarily. The researchers also estimated when the animals differentiated from each other by calculating the rate of molecular change for each species and setting these molecular "clocks" according to dates of separation for other mammal lineages that have been established by the fossil record elsewhere around the world.

The results refute two previously accepted models for
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Contact: Greg Borzo
gborzo@fieldmuseum.org
312-665-7106
Field Museum
12-Feb-2003

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