Mustela putorius
The earliest true polecat was "Mustela stromeri", which appeared during the late Villafranchian. It was considerably smaller than the present form, thus indicating polecats evolved at a relatively late period. The steppe polecat's closest relatives are the European polecat and black-footed ferret, with which it is thought to have shared "Mustela stromeri" as a common ancestor. The steppe polecat likely diverged from the European polecat 1.5 million years ago based on IRBP, though cytochrome b transversions indicate a younger date of 430,000 years. As a species, the steppe polecat represents a more specialised form than the European polecat in the direction of carnivory, being more adapted to preying on larger rodent species; its skull has a stronger dentition, its projections are more strongly developed and its muscles of mastication are more powerful. The steppe polecat's growth rate is also much slower than the European polecat's, as its skull undergoes further development at an age when the European polecat attains full growth. The species may have once been present in Pleistocene central Alaska.