Even-Toed Hoofed Mammals

Scientific Name: Artiodactyla

Gemsbok - Oryx gazella
Photo © Danita Delimont / Getty Images

Even-toed hoofed mammals (Artiodactyla), also known as cloven-hoofed mammals or artiodactyls, are a group mammals whose feet are structured such that their weight is carried by their third and fourth toes. This distinguishes them from the odd-toed hoofed mammals, whose weight is borne primarily by their third toe alone. The artiodactyls include animals such as cattle, goats, deer, sheep, antelope, camels, llamas, pigs, hippopotamuses, and many others. There are about 225 species of even-toed hoofed mammals alive today.

The Size of Artiodactyls

Artiodactyls range in size from the mouse deer (or 'chevrotains') of Southeast Asia that are barely bigger than a rabbit, to the giant hippopotamus, which weighs some three tons. Giraffes, which are not so heavy as the giant hippopotamus, are indeed large in another way—what they lack in bulk they make up for in height, with some species reaching as much as 18 feet tall.

Social Structure Varies

Social structure varies among artiodactyls. Some species, such as water deer of Southeast Asia, lead relatively solitary lives and only seek company during mating season. Other species, such as wildebeest, cape buffalo and American bison, form large herds.

Widespread Group of Mammals

Artiodactyls are a widespread group of mammals. They have colonized every continent except Antarctica (although it should be noted humans introduced artiodactyls to Australia and New Zealand). Artiodactyls live in a variety of habitats including forests, deserts, grasslands, savannas, tundra, and mountains.

How Artiodactyls Adapt

The artiodactyls that inhabit open grasslands and savannas have evolved several key adaptations for life in those environments. Such adaptations include long legs (which enable swift running), keen eyesight, a good sense of smell and acute hearing. Together, these adaptations enable them to detect and evade predators with great success.

Growing Large Horns or Antlers

Many even-toed hoofed mammals grow large horns or antlers. Their horns or antlers are used most often when members of the same species come into conflict. Often, males use their horns when fighting each other to establish dominance during the mating season.

Plant-Based Diet

Most members of this order are herbivorous (that is, they consume a plant-based diet). Some artiodactyls have three- or four-chambered stomach which enables them to digest cellulose from the plant matter they eat with great efficiency. Pigs and peccaries have an omnivorous diet and this is reflected in the physiology of their stomach which has only one chamber.

Classification

Even-toed hoofed mammals are classified within the following taxonomic hierarchy:

Animals > Chordates > Vertebrates > Tetrapods > Amniotes > Mammals > Even-toed hoofed mammals

Even-toed hoofed mammals are divided into the following taxonomic groups:

  • Camels and llamas (Camelidae)
  • Pigs and hogs (Suidae)
  • Peccaries (Tayassuidae)
  • Hippopotamuses (Hippopotamidae)
  • Chevrotains (Tragulidae)
  • Pronghorn (Antilocapridae)
  • Giraffe and okapi (Giraffidae)
  • Deer (Cervidae)
  • Musk deer (Moschidae)
  • Cattle, goats, sheep, and antelope (Bovidae)

Evolution

The first even-toed hoofed mammals appeared about 54 million years ago, during the early Eocene. They are thought to have evolved from the condylarths, a group of extinct placental mammals that lived during the Cretaceous and Paleocene. The oldest known artiodactyl is Diacodexis, a creature that was about the size of a modern-day mouse deer.

The three main groups of even-toed hoofed mammals arose by about 46 million years ago. At that time, even-toed hoofed mammals were by far outnumbered by their cousins the odd-toed hoofed mammals. Even-toed hoofed mammals survived on the fringes, in habitats that offered only hard-to-digest plant foods. That was when even-toed hoofed mammals became well-adapted herbivores and this dietary shift paved the way for their later diversification.

About 15 million years ago, during the Miocene, the climate changed and grasslands became the dominant habitat in many regions. Even-toed hoofed mammals, with their complex stomachs, were poised to take advantage of this shift in food availability and soon surpassed the odd-toed hoofed mammals in number and diversity.