A herbivore is an animal who eats mostly a vegitarian diet. In general the premolars and molars of a herbivore are more or less the same shape, though often the molars are larger than the premolars. The cheek teeth usually have ridges on the crown that are stylised for grinding down fibrous matter. Some animals may specialise in the consumption of one particular plant type and therefore their teeth have adapted accordingly.
Sheep, cattle and horses
Sheep and cattle for example eat a diet that consists mostly of grass. Grass is made of a tough substance known as cellulose. Most animals are not equipt to digest cellulose, but both sheep and cattle have adapted both their teeth and their stomaches in order to get the most out of their grass diet. These animals are known as ruminants. Sheep and cattle have have amazing cheek teeth. The premolars and molars are almost the same in shape (though the molars are usually bigger). Both the premolars and the molars have distinct ridges which effectively grind down grass into a disgusting mush making it easier to swallow.
sheep (Ovis aries) cheek teeth
The cheek teeth of the upper and lower jaw fit together with a close bite with little if any gap in between. This enables the upper and lower molars to glide smoothly across each other in a side-to-side movement, making them a highly efficient chewing machine. This is an advantage for skull collectors particularly if you find several sheep skulls in one area, as I once did, and the mandibles are all mixed up. Simply take one mandible and attach it to any sheep skull, if the cheek teeth of the upper and lower jaws fit together perfectly then you have probably found the right mandible for that particular skull!
sheep (Ovis aries) efficient grinding machine
Horses share a similar diet to that of cattle and sheep. Although horses are not ruminants, their teeth are well designed to cope with a grassy diet so it should come as no surprise that horse cheek teeth are similar to those of cattle. The obvious difference between cattle cheek teeth and horse cheek teeth is that those of the horse are slightly larger than those of cattle. It is said that if you find the back tooth of a horse you should keep it on you at all times and you will never lack money. Unfortunately the tooth must be found by chance for this to work. If you are really lucky you might find the tooth is still attatched to the skull, but I imagine carrying a horse tooth in a horse skull could get quite tiresome!
horse (Equus callabus) left, cow (Bos taurus) right
Rodents and rabbits
Rodents are classified as herbivores, but many are opportunistic and will happily consume small amounts of meat if given the chance. Meat however, makes up only a very small portion of a rodents diet and these animals aren't particular well equipt for hunting. They do however have a great set of tools that perform most efficiently in the art of gnawing. Rodents can be identified by their chisel like front teeth which are designed to chew threw a variety of hard substances. Beavers for example use their's to chew threw tree trunks! Rodent incisors are distinctly long and unlike the incisors of many animal species, these don't have roots. Rather than have rooted insicors which would quickly wear down after so much activity, rodent incisors continue to grow through out their lives. In order to keep their insicors in good shape and prevent them from over growing, rodents must spend a lot of time gnawing. Rodents, rabbits and hares have a large space in their jaws that seperates the insicors from the cheek teeth. This gap is known as the diastema
rabbit (Oryctolagus cuniculus) lower mandible cheek teeth
Rabbits and hares, like rodents have rootless incisors which enable these teeth to continue growing throughout the life of the animal. The cheek teeth of rabbits and hares are also rootless. Rodents however, vary between species. Some rodent species have rootless cheek teeth and some do not.
rabbit (Oryctolagus cuniculus)cheek tooth
The picture above is a side view of a rabbit cheek tooth. This view shows very little difference between the top of the tooth and the bottom. The bottom of the tooth (the root) is an open hole, the top of the tooth is not.
The advantage of having teeth that grow throughout life is that the owner of such teeth does not have to worry about wearing their teeth away.