Saki dentition is built for hard objects. The canines are large, sharply pointed and set at an outward angle, working as wedges that split a husk rather than as stabbing weapons. Behind them, the premolars and molars are low, thick-enamelled and broad, suited to crushing. The combination lets sakis harvest fruit weeks before it ripens, when its defences are at their strongest and competitors cannot open it.
The ecological consequence runs the other way from most primate frugivory. A monkey that grinds seeds kills them, so sakis act as predators on plant reproduction rather than as agents of it. In sandy-soil forests where fruiting is unreliable, this early access is what lets them persist.
The strong colour difference between the sexes is less well explained. Males are black with a striking pale face and females are cryptic brown, which is consistent with sexual selection or with different predation exposure, but neither has been demonstrated in the field.