Eomaia

Eomaia ('dawn mother') is an early fossil eutherian mammal. It is exceptionally well-preserved for a 125 million-year-old specimen.
It was discovered in rocks of the Yixian Formation, Liaoning Province, China. These strata date to the Lower Cretaceous about 125 million years ago (mya).
The fossil is in length and virtually complete. It weighed between . Although the fossil's skull is squashed flat, its teeth, tiny foot bones, cartilages and even its fur are visible.
"Eomaia" is a eutherian. The eutherians are the placental mammals plus some extinct mammals which had not developed a placenta.
What distinguishes the Eutheria from metatherians, a group that includes modern marsupials, are various features of the feet, jaws and teeth.
However "Eomaia" is not a true placental mammal as it lacks some features that are specific to placentals.
"Eomaia" has:
Its discoverers sampled 268 characters from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous period. As a result, they claimed "Eomaia" is at the root of the eutherian "family tree" with a few other fossils.
The "Eomaia" fossil shows clear traces of hair. However this is not the earliest clear evidence of hair in the mammalian lineage, as fossils of the docodont "Castorocauda", discovered in rocks dated to about 164 mya, also have traces of fur.