London, August 25 (ANI): A remarkably well-preserved fossil of a small shrew-like mammal has been discovered in the Liaoning Province in northeast China that provides new information about the earliest ancestors of most of today's mammal species-the placental mammals.
This fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought, filling an important gap in the fossil record and helping to calibrate modern, DNA-based methods of dating the evolution.
The team of scientists led by Carnegie Museum of Natural History paleontologist Zhe-Xi Luo described Juramaia sinensis, a small shrew-like mammal that lived in China 160 million years ago during the Jurassic period. 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 ancestral to placental mammals, Juramaia providesd 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).
"Juramaia, from 160 million years ago, is either a great-grand-aunt, or a 'great-grandmother' of all placental mammals that are thriving today,' said Luo.
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. Most importantly, Juramaia's complete teeth and forepaw bones enable paleontologists to pin-point that it is closer to living placentals on the mammalian family tree than to the pouched marsupials, such as kangaroos.
The finding has been detailed in journal Nature. (ANI)
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