New Research: Fossils of New Squirrel-like Species Support Earlier Origin of Mammals
A research team led by paleontologists at the American Museum of Natural History and the Chinese Academy of Sciences have described three new small squirrel-like species that place a poorly understood Mesozoic group of animals firmly in the mammal family tree. The study, published today in the journal Nature, supports the idea that mammals originated at least 208 million years ago in the late Triassic, much earlier than some previous research suggests.
The three new species—Shenshou lui, Xianshou linglong, and Xianshou songae—are described from six nearly complete 160-million-year-old fossils found in China. The animals, which researchers have placed in a new group, or clade, called Euharamiyida, likely looked similar to small squirrels. They weighed between 1 and 10 ounces and had tails and feet that indicate that they were tree dwellers.
Based on the age of the Euharamiyida species and their kin, the divergence of mammals from reptiles had to have happened much earlier than some research has estimated. Instead of originating in the middle Jurassic (between 176 and 161 million years ago), mammals likely first appeared in the late Triassic (between 235 and 201 million years ago).
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