The most diverse of all living ungulate groups are the Artiodactyla, more commonly known as "artiodactyls" or "even-toed hoofed mammals". There are about 225 living species of artiodactyls spread out over a vast range that includes every continent except Antarctica (their presence in Australia and New Zealand is the result of human introduction).
Artiodactyls are a herbivorous bunch. As a result, many have developed specialized stomachs and digestive habits that enable them to eke out every bit of nutrition from their difficult-to-digest, plant-based diet.
Artiodactyls are divided into three general subgroups based on their stomach anatomy. The non-ruminants, the pseudo-ruminants and the ruminants. The placement of an artiodactyl into one of these three groups depends their stomach—more specifically, the extent to which their stomach is designed for rumination (more on rumination in a moment).
The ruminants—which include cattle, goats, deer, sheep and antelope—have a four-chambered stomach. Members of this group ingest food which then enters the first chamber of the stomach (know as the rumen). There, bacteria helps break down the cellulose-rich food. The food is then regurgitated and rechewed (this is known as "chewing the cud"). After the second chewing, the food is swallowed again and continues through the rest of the stomach chambers and digestive tract.
The pseudo-ruminants (Tylopoda) include camels, llama, alpaca, vicuna and guanaco. These artiodactyls have a three-chambered stomach and undergo a simpler version of rumination.
Finally, the non-ruminants (Suina) include pigs, peccaries and hippopotamusses. Non-ruminants do not partake in rumination. Instead, they have extra chewing teeth and survive on a more varied diet than other artiodactyls, thus eliminating the need for the more complex stomach necessary for rumination.
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