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Long Line of Lemurs
9 August 2005 (All day)
The island of Madagascar is home to lemurs, big-eyed primates that exist nowhere else in the world. When exactly these creatures evolved has long been a mystery. Now, a fossil found in Egypt shows that lemurs, and other primates, originated far earlier than has been thought.
Lemurs are an evolutionary puzzle. Their island home separated from Africa about 145 million years ago, before the origin of placental mammals. So the ancestor of the lemur must have colonized Madagascar more recently, but figuring out when has been tricky. Part of the problem is that DNA and fossil analysis give conflicting data on the age of their lineage. Comparing the accumulated mutations in the DNA of lemurs with those of their closest mainland relatives, the lorises and bush babies, suggests that they all shared a common ancestor 60 million to 65 million years ago. But fossil evidence, the gold standard for natural history, suggests that lemurs actually evolved closer to 20 million years ago. The primate fossil record is notoriously spotty, however, especially for lemurs, so researchers have wondered whether the right bones just haven't turned up yet.
The new fossil may tip the scales in favor of more ancient lemur origins. This year, a team led by Erik Seiffert, a paleontologist at the University of Oxford, U.K., found a well-preserved femur, jawbone, and molar teeth from an extinct primate called Wadilemur elegans. The 35 million-year-old bones show that Wadilemur possessed the lemur's characteristic comb-shaped array of teeth. Although the creature also has key characteristics of bush babies, the teeth identify it as a lemur ancestor, the team reports online this week in Proceedings of the National Academy of Sciences. Seiffert concludes that the Wadilemur fossils prove that the split between lemurs and bush babies occurred at least 35 million years ago and probably earlier.
The study is "really significant," says Robert Martin, an evolutionary biologist at the Field Museum of Natural History in Chicago. Not only does it narrow down the possible origin of lemurs, he says, but it also shores up the "heretical" view that primate evolution in general "began far earlier than indicated by the known fossil record."