Mustelidæ

A descendant of the Creodonta called Cynodictis, which lived in the Eocene, or earliest of the Tertiary periods, is regarded as the forefather of the dog family, but its character is such that it might  as well be said to be the progenitor of the weasel family (Mustelidæ), which may thus be suitably considered the nearest relatives of the Canidæ. These are the small, but alert, muscular and wide-awake animals whose coats, adapted to the cold regions in which most of them live, furnish us with warm and beautiful furs; hence the Mustelidæ may be called the family of "fur bearers." They resemble the dog tribe in the breadth of the skull, and in the dentition, which serves well for the wide variety in their fare; but instead of the long, high-stepping legs of the galloping dogs they have short, strong limbs adapted to creeping, digging, climbing, or swimming. The swimmers are the otters—one marine, the other a denizen of rivers and lakes.