There are 349 extant species, grouped into 131 genera, in Artiodactyla, an order of placental mammals consisting of even-toed ungulates – hooved animals which bear weight equally on two of their five toes with the other toes either present, absent, vestigial, or pointing posteriorly – as well as their descendants, the aquatic cetaceans. Members of this order are called artiodactyls. The order is sometimes named Cetartiodactyla, in reference to the inclusion of cetaceans in the order beginning in the 1990s. Artiodactyls live on every major landmass and throughout the oceans and in a variety of habitats, including forests, grasslands, and deserts. Artiodactyla is divided into four suborders: Ruminantia, Suina, Tylopoda, and Whippomorpha. The suborders are further subdivided into clades and families. Several artiodactyls have gone extinct in recent times, while some domesticated species, including cattle, goats, sheep, and pigs, have a worldwide distribution with population counts of greater than one billion. (Full list...)