The Adaptive Significance of Enamel Loss in the Mandibular Incisors of Cercopithecine Primates (Mammalia: Cercopithecidae): A Finite Element Modelling Study

Abstract

In several primate groups enamel is reduced or absent from the lingual (tongue) side of the mandibular incisor crowns akin to other placental and marsupial mammalian groups such as rodents, lagomorphs and wombats. Here we investigate the presumed adaptation of crowns with unilateral enamel to the incision of tough foods in cercopithecines, an Old World monkey subfamily, using a simulation approach. We developed and validated a finite element model of the lower central incisor of the rhesus macaque (Macaca mulatta) with labial enamel only to compute three-dimensional displacements and maximum principal stresses on the crown subjected to compressive loads varying in orientation. Moreover, we developed a model of a macaque incisor with enamel present on both labial and lingual aspects, thus resembling the ancestral condition found in the sister taxon, the leaf-eating colobines. The results showed that, concomitant with experimental results, the cercopithecine crown with unilateral enamel bends predominantly towards the inside of the mouth, while displacements decreased when both labial and lingual enamel are present. Importantly, the cercopithecine incisor crown experienced lower maximum principal stress on the lingual side compared to the incisor with enamel on the lingual and labial aspects under non-axial loads directed either towards the inside or outside of the mouth. These findings suggest that cercopithecine mandibular incisors are adapted to a wide range of ingestive behaviours compared to colobines. We conclude that the evolutionary loss of lingual enamel in cercopithecines has conferred a safeguard against crown failure under a loading regime assumed for the ingestion (peeling, scraping) of tough-skinned fruits.

A Novel Method for Assessing Enamel Thickness Distribution in the Anterior Dentition as a Signal for Gouging and Other Extractive Foraging Behaviors in Gummivorous Mammals

“…1). This differential distribution of enamel may be a means to resist tensile stress during extractive foraging, while also serving as an adaptation to preserve a sharp incisal edge on these teeth in a fashion similar to that observed among rodents and in Daubentonia, which completely lack enamel on the lingual aspect of the incisors [Noble, 1969;Rosenberger, 1978;Shellis and Hiiemae, 1986;Vinyard et al, 2009;Hogg et al, 2011;Kupczik and Chattah, 2014].…”

Standing on the shoulders of apes: Analyzing the form and function of the hominoid scapula using geometric morphometrics and finite element analysis

“…FEA studies of the scapula have been mostly restricted to orthopedic studies focusing principally on the generation of models of the implanted glenoid (e.g., Friedman et al, ; Lacroix et al, ; Gupta and van der Helm, ; Gupta et al, ; Yongpravat et al, ; Campoli et al, ; Hermida et al, ). Even though other FEA studies have been used in comparative primatology and paleoanthropology, they have been predominantly devoted to the analysis of the craniofacial system during mastication (Kupczik et al, ; Wroe et al, ; Strait et al, ; Curtis et al, ; Dumont et al, ; O'Higgins et al, ; Fitton et al, ; Kupczik and Lev‐Tov Chattah, ). There have been fewer attempts applying FEA to analyze different primate scapulae (Ogihara et al, ), so the present study probably represents one of the first analyses of this anatomical structure using an explicit comparative framework.…”

Evolutionary and Functional Implications of Incisor Enamel Microstructure Diversity in Notoungulata (Placentalia, Mammalia)

“…The loss of lingual enamel could be associated with the category Benamel-band hypsodonty^(Koenigswald 2011), which comprises hypsodont teeth that have enamel only on one or two sides, while the dentine surface covers more than one third of the circumference of the tooth. Stiff enamel is less favored in incisors that need to be more elastic to prevent breakage, as observed in rodents and a few primates (Druzinsky et al 2012;Kupczik and Chattah 2014). The selection of the loss of lingual enamel is Fig.…”