Quantification of enamel decussation in gracile and robust capuchins (Cebus, Sapajus, Cebidae, Platyrrhini)

Abstract

Multiple behavioral and biomechanical analyses have demonstrated that capuchin monkeys (Cebus and Sapajus) are specialized for breaking down hard-object foods as compared to other cebid monkeys. In addition to a complex suite of craniodental adaptations, it has specifically been demonstrated that capuchins possess highly complex dental enamel, with extensive Hunter-Schreger banding and other decussation, that likely serve as an adaptation to resist crack propagation during hard-object feeding. Furthermore, it has been demonstrated that robust capuchins (Sapajus spp., formerly Cebus apella) demonstrate further adaptation for hard-object feeding than other capuchins, routinely breaking down extremely mechanically challenging foods. However, there has been no comparison of dental enamel complexity in robust versus gracile capuchins, to assess whether the dental enamel in Sapajus follows this same pattern of further specialization. Therefore, this study compares dental enamel complexity in images of dental thin sections from a sample of robust versus gracile capuchins using image compression ratio (ICR) analysis. ICR is a variable that correlates with enamel complexity, such that higher ICR values are indicative of increased complexity in the form of enamel decussation. We found no significant difference between robust and gracile capuchins when assessing all teeth in our sample together, however, we did find that robust capuchins have significantly higher ICR values than gracile capuchins for canine teeth, specifically.Our results support prior studies suggesting that robust capuchins are specialized to generate increased masticatory loads with their anterior dentition, specifically, as compared to gracile species.

A novel image processing procedure for the quantitative evaluation of dental enamel prism arrangement

“…Quantitative evaluation of optical micrographs taken with circularly polarized light has proven to be useful for HSB analysis (Hogg & Richardson, 2019). This technique revealed differences of enamel complexity in case of different monkey species, which was attributed to different masticatory loads (Hogg & Elokda, 2021). Mouse enamel was investigated using SEM micrographs by measuring precisely the angle and number of prisms and the complexity of their arrangement was discussed (Smith et al, 2019).…”

Sagittal suture strain in capuchin monkeys (Sapajus and Cebus) during feeding

“…and the untufted forms represent Cebus sp. The more robust morphology of Sapajus relative to Cebus is characterized by larger teeth, thicker mandibular corpora and symphyses, prominent and anteriorly positioned feeding muscles, greater temporalis physiological cross‐sectional area, and more sinuous sagittal sutures (Figure 1; Anapol & Lee, 1994; Byron, 2009; Chai, 2020; Daegling, 1992; Kinzey, 1974; Masterson, 1997; Hogg and Elokda, 2021; Silva Jr., 2001, 2002; Spencer, 2003; Taylor & Vinyard, 2009; Teaford et al, 2020; Wright, 2005). These features are probable adaptations for consumption of tougher foods in Sapajus relative to Cebus , and a seed predation strategy including obdurate foods, such as palm nuts (Cole, 1992; Defler, 1979a; Defler, 1979b; Freese et al, 1981; Izawa, 1979; Kinzey, 1974; Teaford, 1985; Teaford et al, 2020; Wright, 2005).…”

How mangabey molar form differs under routine vs. fallback hard-object feeding regimes

“…With respect to enamel decussation, i.e., the crisscrossing of prisms in enamel, we assessed “enamel complexity”, defined as “any microanatomical feature of dental enamel that increases the heterogeneity of enamel crystallite orientations” ( Hogg & Elokda, 2021 ). The greater the heterogeneity of enamel prism orientations, the more difficult it is for cracks to propagate along prism boundaries ( Hogg & Elokda, 2021 ; Bajaj & Arola, 2009 ). Decussation appears to be more complex in the enamel of mammalian species that experience high loading forces on their teeth ( Hogg & Elokda, 2021 ).…”

“…The greater the heterogeneity of enamel prism orientations, the more difficult it is for cracks to propagate along prism boundaries ( Hogg & Elokda, 2021 ; Bajaj & Arola, 2009 ). Decussation appears to be more complex in the enamel of mammalian species that experience high loading forces on their teeth ( Hogg & Elokda, 2021 ). For example, marked enamel complexity in the canines of robust capuchins has been linked ( Hogg & Elokda, 2021 ) to the high bite forces this species uses to process hard foods ( Wright, 2005 ; Alfaro, Silva Jr & Rylands, 2012 ).…”

“…Decussation appears to be more complex in the enamel of mammalian species that experience high loading forces on their teeth ( Hogg & Elokda, 2021 ). For example, marked enamel complexity in the canines of robust capuchins has been linked ( Hogg & Elokda, 2021 ) to the high bite forces this species uses to process hard foods ( Wright, 2005 ; Alfaro, Silva Jr & Rylands, 2012 ). Although complex decussating enamel resists crack propagation, it is not as wear-resistant as enamel in which prisms are arranged in parallel with the direction of abrasion ( Rensberger, 2000 ).…”