Jaw movement and tooth use in recent and fossil primates

Abstract

Masticatory movements and molar wear facets in species of Tupaia, Galago, Saimiri, and Ateles have been examined using cinefluorography and occlusal analysis. The molars have been compared with those of a fossil series: Palenochtha, Pelycodus and Aegyptopithecus. The extant primates are almost identical in their feeding behaviour, the movements and timing of the masticatory cycle. Food is first puncture‐crushed where the cycle is elongated, the power stroke attenuated and abrasion facets are produced on the molars. Chewing follows, the movements are more complex, the power stroke has two distinct parts and attrition facets are produced. In the primitive forms (Tupaia, Palenochtha), shearing blades, arranged in series (en echelon) were used to cut the food during the first part (Phase I) of the power stroke as the lower teeth move into centric occlusion. This mechanism has been progressively replaced by a system of blade‐ringed compression chambers which cut and compartmentalise the food in Phase I. This is followed by an anteromedially and inferiorly directed movement away from centric occlusion (Phase II) in which the food is ground. In both extant and fossil series there has been a clear trend towards the elongation of Phase II with a corresponding reduction in Phase I. These results suggest that the observed changes in the morphology of the jaw apparatus have probably occurred within the limits set by a pre‐existing behavioral pattern.

Geometric Morphometric Investigation of Molar Shape Diversity in Modern Lemurs and Lorises

“…The relative location of shearing and crushing structures has direct implications for functional morphology. Occlusal wear patterns in primates have been discussed at length in the relevant literature (Kay and Hiiemae, 1974;Hiiemae, 1984) and suggest that during initial stages of Phase I occlusion, the cristid obliqua of the lower molar opposes the postparacrista on the upper molar (Fig. 10).…”

“…Previously, research into molar morphology and adaptation at several different analytical levels has provided a host of methods to apply to extant groups and the fossil record (refer to Ungar, 1998;Teaford, 2000 for comprehensive reviews). Each of these methods address different aspects of function, be it an individual's dietary behavior during life as measured by microwear methods (for example refer to Ungar et al, 2003;Godfrey et al, 2004;Semprebon et al, 2004), shearing and/or crushing capabilities as investigated through comparative and quantitative studies of dental and mandibular morphology (for example refer to Kay and Hiiemae, 1974;Kay, 1975;Szalay, 1974, 1978;Hiiemae, 1978;Kay and Covert, 1984;Ungar and Kay, 1995;Ungar, 1998;Yamashita, 1998a;Strait, 2001;Kirk and Simons, 2001;Ungar et al, 2003, 2004 andreferences therein), or the development of functional dental models (Spears and Crompton, 1996;Evans and Sanson, 2003;Polly, 2004;Evans, 2005 and references therein). Molar function has also been included in larger analyses of mastication dynamics and patterns (refer to Hiiemae, 1984 and references therein).…”

Brief Communication: Intertooth and intrafacet dental microwear variation in an archaeological sample of modern humans from the Jordan Valley

“…Microwear features on facet 9 are most probably created during the chewing cycle from a combination of both compressive forces during phase I of the power stroke and grinding forces (shear and compression) during phase II (Kay and Hiiemae, 1974), though they may not necessarily form in equal measures during the different phases (e.g., Hylander et al, 1987). The intertooth microwear pattern suggests that different locations on the facet experience relatively more or less of these forces.…”

Computational biomes: The ecometrics of large mammal teeth

“…The boreal-temperate moist zone is dominated by several species of deer, which have lophed teeth but never become hypsodont (Heywood, 2010). The lophedness of molar surface reflects the tooth's cutting capacity per unit action (Kay and Hiiemae, 1974). A high cutting capacity in combination with low hypsodonty suggests high functional demands without increased tooth wear, which is characteristic of cool and vegetated habitats, where the major available plant food during the cold season consists of tough, but not very abrasive structural plant parts.…”