Carnassial pair in a sabretooth cat (Smilodon)

The shearing action of the teeth in modern carnvores is generated when the inner surface of the fourth upper premolar (P4) passes outside the outer surface of the first lower molar (M1). The (P4 / M1) combination is referred to as the carnassial pair. This particular combination is characteristic of both feliform and caniform carnivores, and is thus a synapomorphy of these groups. The shearing teeth of extinct Miacid carnivores is a different combination, indicating separate ancestry.

Text material © 2005 by Steven M. Carr