One of the most distinguishing features between mammals with different diets are their teeth (Fig. 1). The dentition of a species has adapted to process a particular, preferred diet.
Carnivores, for example, have very prominent, sharp canine teeth used to apprehend, kill, and butcher their prey. Another set of characteristic carnivore teeth are the carnassials, which are the lower first molar and the upper fourth premolar. These sharp, blade-like teeth shear against one another like a pair of scissors and are used to slice off chunks of flesh .
Carnivoran incisors are relatively small compared to the rest of the dentition, with pointed, close-packed crowns that form a comb-like structure which the animals use to groom their fur .
Omnivores, such as bears, generally have a similar dentition to that of carnivores, with sharp, well-developed canines and small, pointed incisors (Fig. 1). However, their carnassial teeth are not as well-developed as those of strict carnivores . Their teeth are not suited to process tough, fibrous plant foods , which is why they tend to either swallow their food in large, bite-sized chunks or crushed, but not thoroughly ground and chewed.
An excellent example of dentition adaptation to diet within the same genus is that of the polar bear (Ursus maritimus). The polar bear is thought to have evolved between 700,000 and 150,000 years ago – which, in evolutionary terms, is rather recent – from coastal populations of the brown bear (Ursus arctos) . However, while the brown bear is omnivorous, only occasionally eating meat, the polar bear is a strict carnivore, living on a diet of mainly seal flesh and blubber. As a result, the polar bear has reduced molars and premolars compared to omnivorous bears, since he does not require them to grind fibrous plant foods . However, he also does not have the sharp, well-developed carnassials of a true carnivore .
Fig. 1: Upper and lower permanent dentitions of a typical carnivore (dog), omnivore (bear), herbivore (deer), and a human .
Herbivores generally do not have prominent canine teeth. Exceptions are species that have large canines that they use for sexual display or agonistic behaviour. Such is the case with gorillas or male musk deer (Fig. 2), for example.
Unlike carnivores, herbivores have broad, rather flat premolar and molar teeth, which close in perfect occlusion and which they use to thoroughly grind their food in a mortar-and-pestle fashion . Plant matter requires extensive chewing in order to break down tough cellulose cell walls.
Fig. 2: Although an avid herbivore, the male musk deer has long, sharp canine teeth which he uses for agonistic display and in combat with other males (Images: a. from ; b. by Nick Usik).
Fig. 3: Schematic of the dentition of a dog and a human (redrawn after ).
What about humans?
Unlike carnivores, humans have spatulate incisors and reduced, rather blunt canines (Fig. 3). The canines are similar in size to the adjacent incisors and premolars. Our premolars and molars are broad and close in perfect occlusion – ideal for grinding and chewing those fruits, vegetables, and grains. All in all, our dentition has more characteristics in common with that of an herbivore.
 Hillson, Simon. Teeth. Cambridge University Press, 2005.
 Feldhamer, George A. Mammalogy: adaptation, diversity, ecology. JHU Press, 2007.
 Slater, Graham J., et al. "Biomechanical consequences of rapid evolution in the polar bear lineage." PloS one 5.11 (2010): e13870.
 Sacco, Tyson, and Blaire Van Valkenburgh. "Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae)." Journal of Zoology 263.1 (2004): 41–54.
 Hiiemae, Karen M. “Feeding in Mammals”. In: Schwenk, Kurt, ed. Feeding: form, function and evolution in tetrapod vertebrates. Academic Press, 2000.
 Collins, A. Animal Kingdom: Comparative Anatomy. www.slideshare.net/veterinaria_urp/animal-kingdom-comparative-anatomy