TABLE OF CONTENTS - National Zoo

Premolars - These teeth are located just posterior to the canines. On the upper jaw
they reside in the maxillae. They are large in herbivores, where they often closely
resemble the molars in size and complexity, and in certain omnivores and carnivores.
In the latter, the last upper premolar and first lower molar combine when occluded to
form the principal shearing teeth (the carnassials).
Molars - These are generally the most elaborate teeth in the dentition. In the upper
jaw the molars are located in the maxillae. The molars are extremely variable in
pattern. The three-cusped or tritubercular (tribosphenic) arrangement found in
many marsupials, insectivores, and bats, is considered primitive for mammals. Each
occluding pair of upper and lower molars functions as a set of “reversed triangles,”
with the apexes pointing in opposite directions. The lower molars are more complex
than the upper molars, consisting of a triangular anterior portion, the trigonid, and a
squared posterior crushing surface, the “tail” or talonid. Tritubercular teeth are allpurpose
teeth, providing both shearing and crushing surfaces. The addition of
another prominent cusp on the upper molars results in a four-cusped or
quadritubercular molar, an arrangement common in some insectivores and primates.
Omnivores frequently have bunodont molars. Often basically quadritubercular, these
teeth have low, rounded cusps. Effective crushing devices, they are found in pigs,
bears, raccoons, and many primates (including humans). The secodont dentition of
carnivores results from modification of certain cusps into an elaborate shearing
mechanism. A lophodont dentition, present in most herbivores, is identified by
ridges, or lophs, of enamel arranged in various ways between the cusps The tooth
may vary from having a simple ring-like ridge around the margin to having a complex
series of ridges and cross-ridges. When the ridges are formed in to two adjoining
triangles or rings on the same tooth, the arrangement is called bilophodont, as in
lagomorphs and some rodents. In most artiodactyls ridges of enamel take on a
crescent shape, and for this reason the molars are termed selodont.
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