Juramaia sinensis, the earliest known eutherian mammal, walks along a tree branch, was depicted in this illustration by the Carnegie Museum of Natural History. [Photo: Mark Klingler/CMNH/CFP]
A joint research project conducted by scientists from China and the United States has found a well-preserved fossil of the earliest known placental mammal.
The fossil Juramaia sinensis, or "Jurassic mother from China," was found in northeast China's Liaoning Province in 2009 and is approximately 160 million years old, according to a statement issued on Thursday by the Institute of Geology under the Chinese Academy of Geological Sciences.
The finding of the fossil marked a new milestone in evolutionary research, as it proved that mammals began evolving 35 million years earlier than previously thought, the statement said.
The discovery provides new information about the earliest ancestors of today's placental mammals and fills an important gap in fossil records, the statement said.
The age of Juramaia will help to establish a more accurate timeframe for when placental mammals diverged from other mammals, the statement said.
According to the statement, the fossil is composed of an incomplete skull, part of the animal's skeleton and impressions of residual soft tissues such as hair.
The Juramaia was an insectivorous mammal and is estimated to have had a body mass of 13 grams, the statement said.
Placental mammals are characterized by a placenta that provides nourishment to unborn fetuses, said Ji Qiang, a member of the joint research team and a research fellow from the institute.
The origin of placental mammals was an important event in mammalian evolutionary history, as placentals make up more than 90 percent of all living mammals, he said.
The research project was conducted by a team of Chinese and American scientists, including Dr. Zhe-Xi Luo of the U.S.-based Carnegie Museum of Natural History, Drs. Ji Qiang and Yuan Chongxi from the Beijing-based Institute of Geology under the Chinese Academy of Geological Sciences and Dr. Meng Qingjin from the Beijing Museum of Natural History.
Their discovery was published in Nature, a scientific journal, on Thursday.
