Herbivorous mammals span an enormous range of species, from tiny pikas weighing a few ounces to African elephants topping 12,000 pounds. At least six major mammalian orders are primarily or entirely herbivorous, and when you include the many plant-eating rodents, herbivores account for a significant share of all mammal species on Earth.
The Major Groups of Herbivorous Mammals
Herbivores show up across the mammalian family tree, but a handful of orders contain the most familiar examples.
Even-toed hoofed mammals (Artiodactyla): This group includes over 150 species: cattle, bison, sheep, goats, deer, moose, giraffes, camels, pronghorns, and hippos. They’re found on every continent except Australia and Antarctica. Most have four-chambered stomachs specialized for breaking down tough plant material.
Odd-toed hoofed mammals (Perissodactyla): Horses, zebras, rhinoceroses, and tapirs make up this smaller order of about 15 species. All are herbivores with hooves and an odd number of toes on their hind feet.
Elephants (Proboscidea): The two African species and the Asian elephant are strictly herbivorous, consuming grasses, bark, roots, and leaves. African savanna elephants alone represent roughly 6% of all wild land mammal biomass on the planet.
Rabbits, hares, and pikas (Lagomorpha): These small mammals are fully herbivorous, using sharp incisors to clip plant stems and chew bark. Despite their resemblance to rodents, they belong to a separate order.
Sea cows (Sirenia): Manatees and dugongs are the only fully aquatic herbivorous mammals, feeding entirely on underwater vegetation like seagrass and algae.
Rodents (Rodentia): With over 2,000 species making up nearly half of all mammal species, rodents are the largest mammalian order. Most are herbivorous, though many are technically omnivores. Tree squirrels tend to eat more fruit, while ground squirrels are more omnivorous. Beavers, voles, and lemmings are among the most plant-dependent rodents.
Subtypes of Herbivores
Not all herbivores eat the same parts of plants. Scientists divide them into more specific feeding categories based on what they primarily consume.
Folivores specialize in leaves. Howler monkeys, sloths, koalas, and many lemur species fall into this group. Leaves are the most abundant food in a forest canopy, but they’re tough to digest, so folivores typically have long, complex digestive tracts and spend much of the day resting to conserve energy. Frugivores focus on fruit. Fruit bats, kinkajous, and woolly opossums are classic examples, often selecting fruit based on how easy the pulp is to access rather than its color or specific nutrient content. Granivores eat mainly seeds and grains. In desert ecosystems, seed-eating rodents like kangaroo rats are among the most important plant consumers.
Many herbivorous mammals don’t fit neatly into one category. Elephants eat leaves, bark, roots, and fruit depending on the season. Deer browse on leaves in summer and switch to bark and twigs in winter.
How Herbivores Digest Plants
Plants are built from cellulose and other tough fibers that no mammal can break down on its own. Every herbivorous mammal relies on specialized gut bacteria to do the job. Two bacterial groups do most of the heavy lifting across species: Fibrobacter and Ruminococcus. These microbes have been found in the digestive tracts of horses, elephants, rabbits, tapirs, capybaras, rhinoceroses, and cattle.
The way herbivores house these bacteria splits them into two broad camps: foregut fermenters and hindgut fermenters.
Foregut Fermenters
Ruminants like cattle, sheep, deer, and giraffes have a fermentation chamber before the true stomach. In cows, this is the rumen, where microbes break down cellulose and other plant fibers into short-chain fatty acids. These fatty acids are absorbed directly into the bloodstream and become the animal’s main energy source. Later, the bacterial cells themselves are broken down in the acidic stomach, providing the animal’s primary source of protein. This is a remarkably efficient system: the cow essentially feeds its gut bacteria, then digests the bacteria for protein.
Hindgut Fermenters
Horses, zebras, elephants, rabbits, and many rodents ferment plant material in an enlarged cecum or colon, located after the stomach. Hindgut bacteria continue breaking down the tougher plant polymers that survived earlier digestion, and they produce important vitamins including vitamin K, thiamine, and riboflavin. Hindgut fermentation is less efficient at extracting energy from each mouthful, so these animals generally need to eat more relative to their body size.
Teeth Built for Plants
Over the past 20 million years, herbivorous mammals across many unrelated lineages have independently evolved high-crowned cheek teeth, a feature called hypsodonty. These tall, slowly wearing teeth are an adaptation to diets heavy in fibrous, abrasive foods like grasses, which contain silica particles that grind teeth down quickly. Grazing animals like horses and bison have some of the most extreme versions.
Many herbivores also have a gap between their front teeth and their cheek teeth called a diastema. This space lets them clip vegetation with their incisors, then move it to the back of the mouth for grinding, almost like a two-stage processing system. Ruminants like cattle and sheep lack upper incisors entirely, pressing their lower teeth against a tough upper gum pad to tear grass.
Why Some “Herbivores” Eat Meat
Dietary lines blur more than you might expect. Researchers studying urban howler monkeys, normally strict leaf-eaters, recorded 33 instances of individuals eating cooked meat and three cases of dove egg predation. The energy and protein from these meals was minimal, but the researchers concluded the meat likely provided micronutrients that are scarce in plant foods.
White-tailed deer have been documented eating birds and bird eggs. Hippos occasionally scavenge carcasses. These events are rare and opportunistic, not a regular part of the diet, but they suggest that the boundary between herbivore and omnivore is more of a spectrum than a hard line. The label “herbivore” really means an animal whose body, teeth, and digestive system are optimized for plants, even if the animal occasionally supplements with something else.
Coprophagy: A Second Pass at Digestion
Rabbits, hares, and some rodents practice coprophagy, specifically a form called cecotrophy, where they eat a special type of soft fecal pellet produced in the cecum. This isn’t waste in the usual sense. These pellets are rich in nutrients, vitamins, and beneficial bacteria that the animal couldn’t absorb the first time food passed through the gut. By eating them, the animal essentially runs its food through the digestive system twice, extracting far more nutrition from tough plant material. This behavior is so important that rabbits prevented from doing it show measurable declines in growth and reproductive health. For small herbivores living in environments where food quality is low, cecotrophy can be the difference between thriving and starving.