Seed‐breaking forces exerted by orang‐utans with their teeth in captivity and a new technique for estimating forces produced in the Wild

Peter W. Lucas · Charles R. Peters · Stewart R. Arrandale

145 citations0/0 files storedAmerican Journal of Physical Anthropology

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Primate Behavior and Ecology Wildlife Ecology and Conservation Plant and animal studies

Abstract

Orang-utans (Pongo pygmaeus) at the Singapore Zoological Gardens were presented with two thick-shelled edible seeds, Mezzettia parviflora (Annonaceae) and Macadamia ternifolia (Proteaceae) in order to estimate their maximum bite forces. The orang-utans could break the Macadamia seeds in one bite, while those of Mezzettia required repeated attempts. Examination of shell fragments showed that many had scratches and some had clear, but small (ca. 1-2 mm diameter), impressions on them. Building upon this information, semi-imitative tests were performed on the seeds in a universal testing machine by loading them in compression with either flat plates or metal casts of orang-utan cheek teeth. The maximum forces required to break the seeds were similar with both the flat plates and the metal teeth; the average for the Macadamia seeds being about 2,000 N (which forms a minimum estimate for the maximum bite forces in orang-utans) and for the Mezzettia seeds, 6,000 N. The work done with the metal teeth was much greater than with the plates. A mechanical analysis showed that this extra work went into producing permanent impressions ("bite marks") in the shell with the tooth cusps. These impressions were larger than those found on the shells of seeds bitten by the orang-utans. Nevertheless, it is shown theoretically that the size of these indentations can given an estimate of the bite forces used. The maximum force developed in the machine tests with the metal teeth was correlated with the force calculated from analysis of the bite marks. The method is suitable for use in field studies where the marks left on remnants of hard foods eaten by primates may be used to estimate, very roughly, the forces used to produce them.

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References

1984Five New World Primates 1979Mandibular function in Galago crassicaudatus and Macaca fascicularis: An in vivo approach to Stress Analysis of the mandible 1990Hardness as a basis of fruit choice in two sympatric primates 1980Seasonal Variations of Diet Related to Species and Sex in a Community of Cercopithecus Monkeys 1988Bite force, diet, and cranial morphology of fossil hominids 1977The Adaptive Significance of Eskimo Craniofacial Morphology 1983The orang utan. Its biology and conservation 1990Alternative seed-handling strategies in primates: seed-spitting by long-tailed macaques (Macaca fascicularis)

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