Pantolestidae is an extinct family of semi-aquatic, non-placental eutherian mammals that took part in the first placental evolutionary radiation together with other early mammals such as the leptictids. Forming the core of the equally extinct suborder Pantolesta, the pantolestids evolved as a series of increasingly otter-like forms, ranging from the Middle Paleocene (60 mya) Bessoecetor to the Late Eocene (Ergilian) (50-33 mya) Gobiopithecus and Kiinkerishella. They first appear in North America, whence they spread to Europe.