title: Indentation as a technique to assess the mechanical properties of fallback foods.
abstract: A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods-nuts, seeds, and root vegetables-were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads.
authors.affiliation: Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052, USA. peterwlucas@gmail.com
authors.forename: Peter W
authors.initials: PW
authors.lastname: Lucas
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Constantino
authors.forename: Janine
authors.initials: J
authors.lastname: Chalk
authors.forename: Charles
authors.initials: C
authors.lastname: Ziscovici
authors.forename: Barth W
authors.initials: BW
authors.lastname: Wright
authors.forename: Dorothy M
authors.initials: DM
authors.lastname: Fragaszy
authors.forename: David A
authors.initials: DA
authors.lastname: Hill
authors.forename: James J-W
authors.initials: JJ
authors.lastname: Lee
authors.forename: Herzl
authors.initials: H
authors.lastname: Chai
authors.forename: Brian W
authors.initials: BW
authors.lastname: Darvell
authors.forename: Paul K D
authors.initials: PK
authors.lastname: Lee
authors.forename: Tony D B
authors.initials: TD
authors.lastname: Yuen
mesh_terms: D000818:Animals; D001732:Bite Force; D004032:Diet; D004548:Elasticity; D005247:Feeding Behavior; D006244:Hardness; D008422:Materials Testing / Q000379:methods*; D009754:Nuts / Q000737:chemistry; D035281:Plant Tubers / Q000737:chemistry; D011323:Primates / Q000502:physiology*; D012639:Seeds / Q000737:chemistry