This is the VOA Special English SCIENCE REPORT.
Scientists have discovered an extremely small animal they believe could have been the ancestor of all mammals, including humans. The animal lived one-hundred-ninety-five million years ago. It weighed only about two grams. Yet researchers say it had important qualities that link it to mammals. Mammals are warm-blooded animals that feed their young milk from their bodies.
A team of American and Chinese researchers discovered ancient remains of the animal's head bone in southwestern China. Zhe-Xi Luo of the Carnegie Museum of Natural History led the researchers. Their findings were published last month in Science magazine.
The scientists say the animal was one of the smallest mammals that ever lived. But they say the animal's brain was large compared to other mammals. Mr. Luo said the ancient animal had to be very smart because it was able to survive in a world controlled by huge dinosaurs.
The researchers named the tiny animal Hadrocodium wui, which means "large and full head" in the Greek language. Scientists say Hadrocodium was only a little bigger than the smallest mammal now in existence - the bumblebee bat of Thailand.
Mr. Luo says Hadrocodium probably ate insects. And it probably had to eat all the time because of its small size. Researchers also believe the ancient animal had to hide during the day when dinosaurs were hunting. This meant Hadrocodium was able to keep a continuous body temperature in the cold night air.
The researchers compared Hadrocodium's skull to other ancient and modern-day mammals. They say Hadrocodium could be the closest known ancestor of living mammals.
The researchers discovered that the ancient animal had middle ear bones that separated from the lower jaw bone. This is an important quality that separates mammals from the cold-blooded animals called reptiles. The researchers also discovered that Hadrocodium had a large head bone. This suggests that its expanding brain may have pushed the middle ear bones away from the jaw. Mr. Luo say the ancient remains of Hadrocodium prove that some qualities of mammals developed about forty-five-million years earlier than they had believed.
This VOA Special English Science Report was written by Jill Moss.