An order that comprises the modern carnivorous placental mammals and their immediate ancestors. It used to be divided into two suborders, the Fissipedia (mainly land-dwelling) and Pinnipedia (seals, sea lions, walrus), but a more modern classification is into Caniformia (dog-like) and Feliformia (cat-like), with the ‘pinnipeds’ belonging to the former. The carnivores are descended from a single stock of the probably insectivorous, placental mammals of the early Cretaceous, the change being reflected in their dentition. Strong incisors for biting, and canines for piercing, were retained from the insectivorous forms, but in general carnivores acquired modified cheek teeth (carnassials) specialized for shearing. These subsequently became reduced in those carnivores which adopted a herbivorous diet. Hoofs have rarely developed, as claws are used for seizing prey, and digits are never greatly elongated (and, apart from the pollex and hallux, they are not reduced). The first true carnivores were the weasel-like Miacidae of the Palaeocene, which had diverged by the end of the Eocene to give the Canidae (dogs) and Mustelidae (weasels and their allies) as one branch and the Viverridae (Old World civets) and Felidae (cats) as another. According to some authors, the Mustelidae later branched again to give the Phocidae (seals); and the Canidae diversified widely to produce such forms as the Amphicyonidae (‘dog-bears’), Otariidae (sea lions), Procyonidae (raccoons and pandas), and, ultimately, Ursidae (bears); but molecular studies seem to indicate that the Phocidae and Otariidae are descended from a single ancestor which was related to the mustelid–ursid–procyonid stem. Finally, the Hyaenidae (hyenas) emerged in the late Miocene from viverrid stock; this is the youngest of the carnivore families.