WASHINGTON -- A tiny animal that weighed less than a paper clip and lived about 195 million years ago is the smallest true mammal known from the era of dinosaurs, researchers say.
A fossil of the mouse-like animal's skull was found in China, which scientists identified as from a previously unknown species that may have played a key role in the evolution of all mammals, including humans.
Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh, the first author of a study appearing Friday in the journal Science, said the small animal has been named Hadrocodium wui, using a Greek term referring to its head and brain.
Luo said Hadrocodium is a distant and extinct relative of modern mammals. In fact, he said, it could be the ancestor of all mammals, based on current evolutionary theory.
He said the animal's jaw, inner ear structures and a cranium that would house an enlarged brain clearly mark it as an animal on the mammalian family tree.
A group of animals called "mammalian reptiles" split off from the group that were to become dinosaurs about 280 million years ago. Later, in the early Triassic period, another split led to true mammals, most of which were small creatures scampering about to avoid the large dinosaurs that dominated the Earth starting about 200 million years.
It was only after the dinosaurs went extinct, about 65 million years ago, that mammals took over.
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