Spatial variation in mandibular bone elastic modulus and its effect on structural bending stiffness: A test case using the Taï Forest monkeys

Abstract

While our sample did not demonstrate species differences in the degree of spatial autocorrelation of elastic moduli, there may be mechanical effects of heterogeneity (relative strength and rigidity) that do distinguish at the species or subfamilial level (i.e., colobines vs. cercopithecines). The potential connections of heterogeneity to diet and/or taxonomy remain to be discovered.

Diet, feeding behavior, and jaw architecture of Taï monkeys: Congruence and chaos in the realm of functional morphology

“…Le and coauthors offered improved versions of this beam model by first substituting the maximum second moment of area ( I max ) for corpus depth under three successively more accurate (but also more computationally intensive) models . The first of these assumed that bone material stiffness (which covaries positively with mineral content) is homogeneous within and across species.…”

“…Using elastic modulus data determined from microhardness investigations, Le et al then weighted I max by the average elastic modulus ( E ) in each specimen . This effectively incorporates both material and structural information in assessing stiffness; i.e., a mandible with a high I max and high E is stiff and presumably strong.…”

“…Finally, Le et al considered the distribution of E in the mandible and its effect on overall stiffness . This model explored the extent and nature of spatial dependence on overall stiffness and asks the question as to whether material variation serves to mitigate or exacerbate strain gradients in a given jaw .…”

“…Nontargeted remodeling, because it is fulfilling a systemic function, is expected to be diffuse and stochastic. The presence and density of secondary osteons has been investigated in the same taxa examined by Le et al 33 Lad and coauthors found that Taï colobine mandibles tended to have more secondary bone than their cercopithecine compatriots, although the remarkable variation of observed osteon densities within species invites skepticism as to the strength (or existence) of this interspecific signal. 44 Proceeding again from the axiom that a p-value below .05 confers license to unfettered speculation, we can offer the following support for the alternative fatigue strategies outlined previously.…”

“…Le and coauthors offered improved versions of this beam model by first substituting the maximum second moment of area (I max ) for corpus depth under three successively more accurate (but also more computationally intensive) models. 33 The first of these assumed that bone material stiffness (which covaries positively with mineral content) is homogeneous within and across species. This assumption is expedient and wrong but is the operative one in all comparative stud- What does the combining of material and structural data reveal about function, other than providing a more accurate calculation of corpus stiffness?…”