Earliest mammal ancestor described Share This: UPI 2/8/2013 8:17:44 PM NEW YORK, Feb. 8 (UPI) -- A small, half-pound animal with a long furry tail, living on insects, was the common ancestor of almost all mammals, including humans, U.S. researchers say. Scientists completing a 6-year study of the mammalian family tree have identified Protungulatum donnae, a previously little-regarded occupant of the fossil record, as the earliest ancestor of 5,400 living species of placental mammals, The New York Times reported Friday. Placental mammals are creatures that nourish their young in utero through a placenta before a live birth. Researchers used a combination of genetic and anatomical data, publicly available in a database dubbed MorphoBank, to establish the ancestor emerged within 200,000 to 400,000 years after the great dying off of dinosaurs at the end of the Cretaceous period. The study looked "at all aspects of mammalian anatomy, from the skull and skeleton, to the teeth, to internal organs, to muscles and even fur patterns" to determine what the common ancestor likely looked like, project member John R. Wible, curator of mammals at the Carnegie Museum of Natural History in Pittsburgh, said.