It is difficult for sunlight to filter down through the thick canopy of leaves onto the rainforest floor. This makes it hard for plants to grow.
Therefore, most of the herbivores that live off forest floor plants are small.
They have adapted to the small amount of available plant life by becoming highly selective in what they eat.
These small herbivores search for the highest-quality food, usually buds, growing tips, fruits and fleshy roots. Thus, they make up in high-energy foods what they miss in bulk.
To enable them to nip out the right piece of a chosen food plant, they use their small, delicate mouths and sensitive lips. If the eat a piece of leaf or fibrous twig by accident, they are able to reject it quickly with their lips and tongue.
No large herbivores feed directly on the forest floor, as there is insufficient plant growth to support them.
A few large species, including, elephants, okapis and bantengs, feed on the understory layer while standing on the forest floor.
These animals are known as bulk eaters. They are not fussy about the quality of the food they eat; their stomachs are adapted to cope with the toughest and most fibrous materials.
The bodies of bulk feeders are designed to enable them to obtain food from above their heads.
The okapi has an elongated neck and a long muscular tongue with a rough, scale-like surface to enhance its efficiency as a kind of billhook.
The banteng, which lives at the edge of the rainforest as well as within the rainforest itself, also has a very long tongue. It prefers twigs and leaves to branches.
The elephant has a long trunk and a short neck. The trunk, which consists of the nose and the upper lip fused together, is sensitive and strong. The elephant can use its trunk to choose a single ripe fruit from among many unripe ones, or to lift up a fallen tree trunk.
Elephants tend to eat fibrous, woody plant material; they tear down whole branches and then eat them.
The lowland gorilla, Gorilla gorilla, of West Africa spends its life on the ground. It climbs into the understory to feed and occasionally sleeps in low trees.
Gorillas usually gather their food in trees and eat it on the ground. Their diet consists of nuts, berries, fruits, leaves and shoots
Like most monkeys and apes, gorillas use their hands to grab food.
The gorilla's fingers are thick and stubby. It must use its lips and teeth to remove pits and skin from fruit.