Pw. Lucas et al., SEED-BREAKING FORCES EXERTED BY ORANGUTANS WITH THEIR TEETH IN CAPTIVITY AND A NEW TECHNIQUE FOR ESTIMATING FORCES PRODUCED IN THE WILD, American journal of physical anthropology, 94(3), 1994, pp. 365-378
Orang-utans (Pongo pygmaeus) at the Singapore Zoological Gardens were
presented with two thick-shelled edible seeds, Mezzettia parviflora (A
nnonaceae) and Macadamia ternifolia (Proteaceae) in order to estimate
their maximum bite forces. The orang-utans could break the Macadamia s
eeds in one bite, while those of Mezzettia required repeated attempts.
Examination of shell fragments showed that many had scratches and som
e had clear, but small (ca. 1-2 mm diameter), impressions on them. Bui
lding upon this information, semi-imitative tests were performed on th
e 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 b
eing about 2,000 N (which forms a minimum estimate for the maximum bit
e forces in orang-utans) and for the Mezzettia seeds, 6,000 N. The wor
k done with the metal teeth was much greater than with the plates. A m
echanical analysis showed that this extra work went into producing per
manent 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 th
at the size of these indentations can give an estimate of the bite for
ces used. The maximum force developed in the machine tests with the me
tal teeth was correlated with the force calculated from analysis of th
e bite marks. The method is suitable for use in field studies where th
e marks left on remnants of hard foods eaten by primates may be used t
o estimate, very roughly, the forces used to produce them. (C) 1994 Wi
ley-Liss, Inc.