The mouse-like creature was covered in heavy fur
A mouse-like fossil found in north-eastern China has been identified as the earliest known member of the family of mammals whose descendents include humans.
The small, furry creature lived at the same time that dinosaurs ruled the surface of the Earth, 125 million years ago.
The fossil was found in Liaoning Province.
It belongs to the family of mammals known as "eutherians" or "placentals", which means its young would have developed in a placenta in the female's uterus.
The Chinese fossil represents the earliest known ancestor of all placentals, including our own group of mammals, the primates.
Tree climber
The animal was about the size of a mouse and covered in heavy fur.
It lived between 140 million and 110 million years ago, making it nearly twice as old as many famous dinosaurs like Tyrannosaurus rex or Triceratops.
It has been named Eomaia scansoria, meaning first - or earliest - climber.
Its skeleton, although flattened into a section of rock, is nevertheless remarkably complete.
Most ancient mammals are only known by a few teeth or bones, but the entire body of E. scansoria, including its heavy fur, is still clearly visible.
Analysis of the fossil skeleton indicates the animal was an agile creature with a powerful ability to climb.
And the researchers, who report the their findings in the journal Nature, suggest this may explain how it managed to survive during the age of the dinosaurs: by climbing and hiding in trees.