CREODONTA. An order or sub-order of primitive Car nivora characteristic of the older Tertiary. The creodonts were the flesh-eating animals of the northern continents during the Eocene, and included a number of families of diverse or partly parallel specialization, from one of which, the Miacidae, were descended the various families of modern Carnivora. They are distinguished by certain primitive characters, the small brain, separate scaphoid and lunar bones of the carpus, and lack of ossification of the tympanic bulla. Except in the family Miacidae they lack the specialization of p4 as "carnassials" characteris tic of the fissiped Carnivora ; but another pair of teeth may be enlarged and specialized instead (m2 in Oxyaenidae, mi in Hyaenodontidae). They are distinguished from Insectivora and associated with the modern Carnivora by the enlargement of the canines into powerful laniary teeth, reduction of incisors, the more sectorial characters of the cheek teeth, heavier muzzle and jaws with strong zygomatic arches, also by a number of characters: in the feet (astragalar trochlea narrower with inner keel imperfect, astragalar foramen present, phalanges more elongate and curved, etc.).
The earliest Creodonta are the Oxyclaenidae of the Paleocene, with primitive tritubercular teeth, the molars sub-equal, none of them enlarged as carnassials. These gave rise to a number of different specialized families of creodonts during the Eocene. The Arctocyonidae had flattened bear-like teeth and were plantigrade, with sharp compressed claws like the bears.
The Miacidae include a considerable variety of small or medium-sized creodonts with more or less tuberculo-sectorial molars, the first molar the largest of the three and progressively specialized along with the fourth premolar of the upper jaw into enlarged shearing teeth or carnassials. The teeth behind the car nassial are in some genera (Vulpavus, Oodectes) of similar shear ing type but smaller size ; in other genera they are flattened crush ing teeth, two in number (Didymictis, Viverravus), or three (Miacis, Uintacyon, Vassacyon). In the Upper Eocene the Miacidae give rise, through inter mediate genera such as Proda phaenus, Procynodictis, Cynodic tis, Cynodon and others, to the primitive fissiped Carnivora of the Oligocene.
The Oxyaenidae included larger predacious types, Oxyaena re sembling a wolverine, Patrio f elis reaching the size of a bear with massive hyena-like teeth, Palaeo nictis of more feline characters, the smaller Limnocyons, analo gous in teeth, proportions and probable habits, to modern weasels and martens.
The Hyaenodontidae include many and various types in North America, Europe. Asia and Africa. In the earliest forms, Sinopa, Proviverra, Tritemnodon, of the Lower and Middle Eocene, the teeth are tuberculo-sectorial, the molars not very different in size, and the skull is long and slender, the proportions of body and limbs like those of the modern viverrids (civet family) except for the very long and heavy tail. In Pterodon and Hyaenodon of the Upper Eocene and Oligocene, the teeth are more completely sectorial, the size larger and proportions of skull and limbs are more like those of wolves. Widespread in the Upper Eocene and Oligocene, late survivors occur in the Indian Miocene.
The most diverse and specialized group of the creodonts is the Mesonychidae, distinguished by the loss of any shearing action of the teeth, the cusps becoming high, round, blunt-tipped, adapted probably for crushing and piercing some hard, shelly food. The muzzle and jaws are elongate, the limbs and feet in some species slender and cursorial as in the wolf, while others attain large size and massive proportions comparing with the larger bears. The toes are tipped with flattened hoofs instead of claws. These are found in the Eocene of western North America, western Europe and central Asia. Several of them equalled or exceeded the largest living Carnivora in size of skull, and in the Upper Eocene of Mongolia the gigantic Andrewsarchus has a skull three feet long, the largest known carnivore, even allowing for the probability that the skull was relatively large in proportion to the skeleton.
(W. D. M.)