Tuesday, September 24, 2013

What Do I Eat? - Herbivores

The word "herbivore" means plant-eater.  It derives from the Latin words herba (plant or grass) and vorarae (devour).

The teeth of herbivorous mammals have evolved to eat a diet that is mainly composed of plants.  Often herbivores have upper and lower incisors are quite sharp and shaped like chisels.  In some mammals like rodents and rabbits these incisors meet or nearly meet and allow them to bite cleanly through plant stems. 

Muskrat (Ondotra zibethicus) skull showing the large incisors

The incisors of these animals grow throughout their lives and are worn down through constant chewing.  Only the front surface of their incisors is covered with hard enamel - causing the back of their teeth to wear faster and giving their incisors that chisel-shaped profile.

North American Beaver (Castor canadensis) skull showing chisel-shaped profile of incisors

This sharp tooth profile allows them to cut easily through non-woody plants and even woody stems.

Branch showing marks from beaver teeth

The molars of herbivorous mammals are generally flat with a chewing surface that is covered with several ridges.  These ridges allow the teeth to be used to grind leaves, stems, bark, etc. so that they may be more easily digested.  In some animals (such as rodents) the surface of the molars is quite flat and the ridges are small.

Beaver molars
Muskrat molars

Other herbivores such as White-tailed Deer (Odocoileus virginianus) have molars that while generally flat have much larger ridges.

White-tailed Deer (Odocoileus virginianus) molars

There is something interesting about the teeth of White-tailed Deer.  White-tailed Deer (and all other deer) do not have top incisors.  This means that they are unable to bite directly through plants like those species that have opposing incisors.

White-tailed Deer (Odocoileus virginianus) skull - note the lack of upper incisors

Instead their bottom incisors come in contact with a rough pad on their upper jaw, enabling them to tightly grab onto plants which they then tear or twist off.  Branches that are browsed by White-tailed Deer are often cut on one side (by the lower incisors) and roughly torn on the other rather than being neatly cut like plants chewed by rodents.

White-tailed Deer (Odocoileus virginianus) skull - Lower incisors meet up with a rough pad on the upper jaw.

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