The even-toed ungulates (order Artiodactyla) are ungulates (hoofed mammals) whose weight is borne approximately equally by the third and fourth toes, rather than mostly or entirely by the third as in odd-toed ungulates (perissodactyls), such as horses.
The name Artiodactyla comes from (Greek: ἄρτιος (ártios), "even", and δάκτυλος (dáktylos), "finger/toe"), so the name "even-toed" is a translation of the description. This group includes suids (family Suidae), peccaries (family Tayassuidae), hippos (family Hippopotamidae), camelids (family Camelidae), chevrotains or mouse deer (family Tragulidae), deer (family Cervidae), musk deer (family Moschidae) giraffes (family Giraffidae), antilocaprids (family Antilocapridae), bovids (family Bovidae). Some exclude whales (infraorder Cetacea), although DNA sequence and anatomical data indicate they share a common ancestor, making the group paraphyletic. This school of thought names the joint group Cetartiodactyla (from Cetacea and Artiodactyla). Conversely, Grove and Grubb, 2011, citing Heglen and others, include Cetacea as a sister group of Hippopotamidae, since they are "deeply nested" within the phylogeny of the Artiodactyla, rather than a sister group which could be comprehended by a parent "Cetartiodactyla". They further contend, on the same authority, that just as Carnivora subsumed Pinnipedia without a name change, no name change is required for Artiodactyla. Despite this, other say that cetaceans are still only close living relatives of even-toed ungulates.
A further distinguishing feature of the group is the shape of the astragalus (talus), a bone in the ankle joint, which has a double-pulley structure. This gives the foot greater flexibility.
They date back to the Early Eocene