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.
As the earliest known fossil ancestor to placental mammals, Juramaia provides fossil evidence of the date when eutherian mammals diverged from other mammals: metatherians (whose descendants include marsupials such as kangaroos) and monotremes (such as the platypus).
As Luo explains, "Juramaia, from 160 million years ago, is either a great-grand-aunt or a great-grandmother of all placental mammals that are thriving today."
The fossil of Juramaia sinensis was discovered in the Liaoning Province in northeast China and examined in Beijing by Luo and collaborators: Chong-Xi Yuan and Qiang Ji from the Chinese Academy of Geological Sciences and Qing-Jin Meng from the Beijing Museum of Natural History, where the fossil is stored.
The name Juramaia sinensis means "Jurassic mother from China."
The fossil has an incomplete skull, part of the skeleton, and, remarkably, impressions of residual soft tissues such as hair.
Juramaia's complete teeth and forepaw bones enable paleontologists to pinpoint that it is closer to living placental
|Contact: Cheryl Dybas|
National Science Foundation