for National Geographic News
A new genetic study claims to have settled a long-standing debate about which living group of mammals is most closely related to primates, which include monkeys, apes, and lemurs.
Our nearest nonprimate relatives are not tree shrews as once thought, researchers say—but another group of tree-dwelling mammals known as colugos, also known as flying lemurs.
Colugos are squirrel-size creatures that live in the rain forests of Southeast Asia. Only two species are known to exist.
Like flying squirrels, colugos have a wide membrane of skin between their limbs that, when fully extended, forms a kind of sail—allowing the animals to glide from tree to tree. (See an Asian primate, the tarsier, in flight.)
Previous DNA-based studies had suggested that primates, tree shrews, and colugos are closely related, forming a single evolutionary grouping that can be traced back to a common ancestral species. (Related news: "Fossils of 'Most Primitive Primate' Found Near Yellowstone" [February 1, 2007].)
But experts have continued to debate when and in what order the three groups diverged from one another.
The new study finds that the ancestors of tree shrews split off first, and then the primate and colugo lineages diverged. That means that colugos are primates' closest evolutionary cousins.
"Our molecular trees indicate that [primates and colugos] split approximately 86 million years ago, more than 30 million years before modern primates or colugos appear in the fossil record," said study co-author William Murphy.
Murphy and Jan Janečka, both of Texas A&M University in College Station, led the team of U.S. and German researchers who will publish their findings in tomorrow's issue of the journal Science.
The researchers performed a comparative analysis of rare genetic changes in the different mammal groups.
Seven such changes were found in common between primates and colugos, compared to only one between primates and tree shrews.
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