A well-preserved fossil discovered in northeast China provides new information about the earliest ancestors of most of today's mammal species--the placental mammals.
According to a paper published today in the journal Nature, the fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought.
It fills an important gap in the fossil record and helps to calibrate modern, DNA-based methods of dating evolution.
The paper, by a team of scientists led by Carnegie Museum of Natural History paleontologist Zhe-Xi Luo, describes Juramaia sinensis, a small shrew-like mammal that lived in China 160 million years ago during the Jurassic.
Juramaia is the earliest known fossil of eutherians--the group that evolved to include all placental mammals, which provide nourishment to unborn young via a placenta.
http://www.physorg.com/news/2011-08-discovery-million-year-old-fossil-milestone-early.html
