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a Data compiled from Martin (1990), Swindler (2002), Tattersall (1982).

a Data compiled from Martin (1990), Swindler (2002), Tattersall (1982).

are good at arresting cracks once they start. Brittle foods are the opposite; they propagate cracks readily once they are initiated. Elastic modulus is a measure of stiffness or resistance to bending. Hardness is resistance to indentation. The relationship between toughness (R) and elastic modulus (E) describes how plants mount mechanical defenses against herbivory (Agrawal et al., 1998; Lucas, 2004; Lucas et al., 2000). Stress-limited foods (VeR) are brittle and shatter when sufficient stress levels are reached. A plant that invests in this type of defense relies on herbivores being unable to generate the required force to fragment it. Displacement-limited defenses (Vr/E) depend on predators being unable to strain the plant part to failure (Agrawal et al., 1998). Thin materials, such as leaves, tend to rely solely on toughness as a defense.

In order for herbivores to overcome physical plant defenses, it would be advantageous for them to possess morphologies that are suitable for fragmenting plant parts with distinct mechanical properties. Tough foods should require bladed features to initiate and guide crack formation since they do not easily propagate cracks. The carnassial teeth of carnivores represent a bladed system for fracturing soft, tough foods. Flat, tough foods such as leaves also require crests, though in a configuration that resembles a "milling machine" (Hiiemae and Crompton, 1985). Hard/brittle foods are best fractured with blunt cusps that can tolerate the high stresses involved in overcoming stress-limited defenses. In addition, fine reduction of hard foods would be made easier with a loose occlusal fit between a cusp and basin to locate weak areas in the food (Lucas, 1979). In this chapter, we examine this relationship between tooth form and diet in the varied dentition of lemurs.

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