For Immediate Release Contact: Greg Borzo (312) 665-7100 (For Media Use Only) gborzo@fieldmuseum.org 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 how mammals colonized Madagascar. One model says mammals were already on Madagascar when the land mass broke away from Africa 165 million years ago. The other suggests they came from Africa via a land bridge, which is supposed to have existed 45 million to 26 million years ago. The new research establishes that Carnivora arrived on the island more recently than either of these models predicted, strongly contradicting both models. “At long last, statistical methods for estimating divergence ages among organisms are becoming sufficiently sophisticated that we can have confidence in the accuracy of the age estimates,” notes Anne Yoder, Associate Professor of evolutionary biology at Yale University, Field Museum research associate, and lead author of the Nature paper. The study provides further evidence that lemurs also colonized Madagascar in a single over-water event, in this case a much older episode, which the team estimates occurred about 66 million to 62 million years ago. This confirms that crossing a large water barrier, followed by colonization and diversification, has occurred very rarely among land mammals. Continue