page_title: Ungulate
section_title: Artiodactyl evolution
hierarchical_section_title: Ungulate / Evolution / Artiodactyl evolution
caption_attribution_description: Arctocyon
context_page_description: Ungulates are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, and hippopotamuses. Cetaceans are also even-toed ungulates although they do not have hooves. Most terrestrial ungulates use the tips of their toes, usually hoofed body weight while moving.
  The term means, roughly, "being hoofed" or "hoofed animal". As a descriptive term, "ungulate" normally excludes cetaceans, as they do not possess most of the typical morphological characteristics of ungulates, but recent discoveries indicate that they were descended from early artiodactyls. Ungulates are typically herbivorous and many employ specialized gut-bacteria to allow them to digest cellulose. Some modern species, such as pigs, are omnivorous, while some prehistoric species, such as mesonychians, were carnivorous.
context_section_description: The artiodactyls were thought to have evolved from a small group of condylarths, Arctocyonidae, which were unspecialized, superficially raccoon-like to bear-like omnivores from the Early Paleocene
  (about 65 to 60 million years ago). They had relatively short limbs lacking specializations associated with their relatives (e.g. reduced side digits, fused bones, and hooves), and long, heavy tails.  Their primitive anatomy makes it unlikely that they were able to run down prey, but with their powerful proportions, claws, and long canines, they may have been able to overpower smaller animals in surprise attacks. Evidently these mammals soon evolved into two separate lineages: the mesonychians and the artiodactyls.
  Mesonychians were depicted as "wolves on hooves" and were the first major mammalian predators, appearing in the Paleocene.  Early mesonychids had five digits on their feet, which probably rested flat on the ground during walking (plantigrade locomotion), but later mesonychids had four digits that ended in tiny hooves on all of their toes and were increasingly well adapted to running. Like running members of the even-toed ungulates, mesonychids (Pachyaena, for example) walked on their digits (digitigrade locomotion). Mesonychians fared very poorly at the close of the Eocene epoch, with only one genus, Mongolestes, surviving into the Early Oligocene epoch, as the climate changed and fierce competition arose from the better adapted creodonts.
  The first artiodactyls looked like today's chevrotains or pigs: small, short-legged creatures that ate leaves and the soft parts of plants. By the Late Eocene (46 million years ago), the three modern suborders had already developed: Suina (the pig group); Tylopoda (the camel group); and Ruminantia (the goat and cattle group). Nevertheless, artiodactyls were far from dominant at that time: the perissodactyls were much more successful and far more numerous. Artiodactyls survived in niche roles, usually occupying marginal habitats, and it is presumably at that time that they developed their complex digestive systems, which allowed them to survive on lower-grade food. While most artiodactyls were taking over the niches left behind by several extinct perissodactyls, one lineage of artiodactyls began to venture out into the seas.
caption: Arctocyon an arctocyonid
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