The common ancestor of all mammals, including us

Go to the NYT website to see an artist's drawing of the creature. Here's a bit of description:

Pulled out of obscurity and given some belated stature by an artist’s brush, the animal — roughly the size of a rat — hardly looks the part of a progenitor of so many mammals... It weighed no more than half a pound, had a long furry tail and lived on insects.

Mammy!