Artiodactyla

Artiodactyla is an order of mammals known as even-toed ungulates, characterized by bearing most of the body's weight on the third and fourth toes of each foot (paraxonic locomotion). The other toes are usually reduced or absent. This contrasts with the odd-toed ungulates (Perissodactyla). Artiodactyls range from small chevrotains to large bovids and giraffids and occupy a broad array of habitats worldwide.

Diversity and classification: The order includes several families, such as Tragulidae (chevrotains), Moschidae (musk deer), Suidae (true pigs), Tayassuidae (peccaries), Camelidae (camels and llamas), Giraffidae (giraffes and okapis), Cervidae (deer), Bovidae (cattle, sheep, goats, antelopes), and Antilocapridae (pronghorn). In some classifications Moschidae is treated as a subfamily within Cervidae. In modern systematics, cetaceans (whales and dolphins) are placed within a broader clade, Cetartiodactyla, reflecting their close evolutionary relationship to artiodactyls.

Ecology and anatomy: Artiodactyls inhabit a variety of ecosystems and are predominantly herbivorous. Many are ruminants, possessing a multi-chambered stomach adapted for foregut fermentation, though some groups such as pigs are nonruminant omnivores. Dentition generally reflects grazing or browsing habits, and several species bear horns, tusks, or antlers.

Evolution and fossil record: Artiodactyls first appear in the fossil record in the early to middle Eocene (roughly 55–40 million years ago). Their diversification produced the diverse lineages that include modern hoofed mammals. Molecular and fossil evidence support a close relationship between artiodactyls and cetaceans, leading to the contemporary concept of Cetartiodactyla.