Figure 3.

Angle measurement used to measure the patterning cascade mode of cusp development. The b-a-c angle should predict the height and number of short cusps (d, d₂, and b₂) because sharp teeth (small angle) should have fewer cusps and cusps that are more unequal in height than blunt teeth (large angle). The patterning cascade also makes some morphological variation rare or “forbidden,” such as a cusp missing in the middle of a cascade or a disproportionally large or small cusp, requiring a change in the patterning cascade parameters. The kinds of teeth (Fig. 1B) and variation in cusp positions (Figs. 4 and 5) encountered support the division between “allowed” and “forbidden” variation. Note that in many mammals, differential growth between cusps can alter cusp positions along the crown after their developmental initiation (19) and that the cascading pattern also can be obscured by conules (small cusps) that form between main cusps late in development.