Artiodactyla (cohort Ferungulata, superorder Paraxonia) The even-toed ungulates, an order of mammals that includes the camels, pigs, and ruminants, together with numerous extinct varieties. They are the most successful of the hoofed animals. They are descended from the Condylarthra, and underwent a spectacular burst of adaptive radiation in Eocene and early Oligocene times. They are terrestrial or amphibious herbivorous mammals. Except for the camels the gait is unguligrade The axis of the foot is paraxonic; the first digit is absent, the second and fifth often reduced or lost. The digits terminate in hoofs, the third and fourth of equal size, usually flattened on the inner and ventral surfaces. The dentition is specialized; the upper incisors are lost in some species, the lower incisors biting against the hardened gum of the premaxilla; the canines may form tusks; the premolars are not molarized (i.e. adapted for grinding, as in many Perissodactyla), elongated hypsodont molars providing grinding surfaces, the four cusps often being developed into longitudinal ridges. The tongue is large, mobile, protrusible, pointed, and the papillae are often horny. The stomach is elaborate. The brain is moderately well developed in later forms, although the cerebral hemispheres only partly cover the cerebellum, and in early and some modern forms (e.g. hippopotamus and pig) the brain is small. The olfactory sense is important. Visual, auditory, olfactory, and tactile signals are important in communication.

Artiodactyla (artiodactyls; cohort Ferungulata) Even-toed ungulates, an order of mammals that includes the living camels, pigs, and ruminants. Descended from the Condylarthra, they underwent a spectacular burst of adaptive radiation in Eocene and early Oligocene times, largely replacing the initially more numerous Perissodactyla. The ankle bone (astragalus) is specialized in artiodactyls to give better spring. The axis of the foot is paraxonic (passing between the third and fourth digits). In primitive, four-toed types, e.g. the pig, the first digit is absent; in advanced forms the second and fifth digits are also reduced or lost. Early forms had an unspecialized dentition, but in the course of evolution the upper incisors were lost in some species, the lower incisors biting against the hardened gum of the upper jaw, an adaptation to a herbivorous diet.

Artiodactyla An order of hooved mammals comprising the even-toed ungulates, in which the third and fourth digits are equally developed and bear the weight of the body. The order includes cattle and other ruminants (see Ruminantia), camels, hippopotamuses, and pigs. All except the latter are herbivorous, having an elongated gut and teeth with enamel ridges for grinding tough grasses. Compare Perissodactyla.

ar·ti·o·dac·tyl / ˌärtē-ōˈdaktl/ • n. any ungulate mammal of the order Artiodactyla, with two main toes on each foot, including camels, pigs, hippopotamuses, and ruminants. • adj. of or relating to artiodactyls.