Predicting bite force in mammals: two-dimensional versus three-dimensional lever models

Abstract

SUMMARYBite force is a measure of whole-organism performance that is often used to investigate the relationships between performance, morphology and fitness. When in vivo measurements of bite force are unavailable, researchers often turn to lever models to predict bite forces. This study demonstrates that bite force predictions based on two-dimensional (2-D) lever models can be improved by including three-dimensional (3-D) geometry and realistic physiological cross-sectional areas derived from dissections. Widely used, the 2-D method does a reasonable job of predicting bite force. However, it does so by over predicting physiological cross-sectional areas for the masseter and pterygoid muscles and under predicting physiological cross-sectional areas for the temporalis muscle. We found that lever models that include the three dimensional structure of the skull and mandible and physiological cross-sectional areas calculated from dissected muscles provide the best predictions of bite force. Models that accurately represent the biting mechanics strengthen our understanding of which variables are functionally relevant and how they are relevant to feeding performance.

Accuracy of mandibular force profiles for bite force estimation and feeding behavior reconstruction in extant and extinct carnivorans

“…These results support the long-held suspicion that Thomason's (1991) jaw musculature method greatly underestimates bite force (see Therrien, 2005a;Ellis et al, 2008;Davis et al, 2010). However, the congruence between empirically determined and hollow-model-derived bite force values expressed relative to P. leo suggests that the jaw musculature method might produce accurate bite force estimates for this felid (see Sakamoto et al, 2010).…”

“…However, the congruence between empirically determined and hollow-model-derived bite force values expressed relative to P. leo suggests that the jaw musculature method might produce accurate bite force estimates for this felid (see Sakamoto et al, 2010). The poorer performance of the jaw musculature method has been ascribed to a variety of issues, such as the fact that the method: (1) does not account for interspecific variation in jaw muscle pennation, (2) assumes that muscle cross-sectional area and lever arm length correlate directly with bite force, and (3) considers the mandible as a two-dimensional object only, which overestimates the crosssectional area of the masseter and pterygoid muscles and underestimates the cross-sectional area of the temporalis muscle in many carnivorans (Wroe et al, 2005;Ellis et al, 2008;Davis et al, 2010;Tseng and Binder, 2010). Thus mandibular force profiles, particularly the hollow mandible model, are a more accurate and far simpler method to estimate bite force than Thomason's (1991) jaw musculature method.…”

Sex reversal induces size and performance differences among females of the African pygmy mouse, Mus minutoides

“…Most of these studies have clearly demonstrated the link between osteology, muscular activity and biting performance at the intraspecific as well as interspecific levels (e.g. Herrel et al, 1999;Aguirre et al, 2002;Davis et al, 2010;Santana et al, 2010). Morphology has also been shown to be a driver of performance and fitness via intra-sexual competition (Herrel et al, 2010;Lailvaux et al, 2004).…”

Go big or go fish: morphological specializations in carnivorous bats

“…Separated by at least 55 Myr of evolution [41], the two piscivorous species in the dataset (Noctilio leporinus and Myotis vivesi) have converged in cranial morphologies characterized by a short, broad and tall or dorsally projected rostrum, and broad zygomatic arches. This morphology results in a shorter out lever that is suited for producing high bite forces at low gapes [71,72], and potentially confers more resistance during cyclical molar chewing [73]. Consistent with these specializations, piscivorous bats feed using narrow gapes and masticate their prey for a prolonged period of time [25]; fishes are laterally compressed and contain sharp bones that could be harmful if not chewed meticulously before swallowing.…”