Taxonomic Implications of Molar Morphology Variability in Capuchins

Abstract

Tooth morphology has been widely used to infer taxonomic affinities. Both morphological and genetic analyses have revealed significant differences among capuchins, suggesting that two distinct monophyletic groups exist: the gracile capuchins (Cebus) and the robust capuchins (Sapajus). We developed a geometric morphometrics (GM) model to determine if the two groups also show distinct molar shapes and to explore the influence of size, phylogeny, and biogeography in shaping molar morphology. We characterized first and second molar crown shape variability in seven species representative of the two genera (Cebus albifrons, C. olivaceus, Sapajus apella, S. robustus, S. libidinosus, S. nigritus, and S. xanthosternos), using two-dimensional (2D) and three-dimensional (3D) GM. The results showed that 2D GM discriminated the two groups better than 3D GM, possibly because it accounted for cusp position and crown contour, but not cusp height, which may be a useful trait for inferring adaptive foraging ecology but presents a risk of homoplasy. In addition, the presence of a phylogenetic signal in the first molar shape (2D) is likely to reflect similarity to the ancestral condition and provides evidence of gradual evolution of molar robustness in the robust clade. We suggest that the shape of the first molar is informative about phylogenetic affinities, whereas the shape of the second molar is more informative about biogeographic variability. However, molar shape similarities may be affected by convergent evolution, as environmental factors in different biogeographical regions may have a significant effect on molar morphology, as seen in the closely related capuchins. Int J Primatol

Further morphological evidence on South African earliest Homo lower postcanine dentition: Enamel thickness and enamel dentine junction

“…A study on molar GM in capuchins suggests that molar shapes reflect different influences depending on molar position (i.e., M 1 represents phylogenetic affinities and M 2 indicates biogeographic variability; Delgado et al, 2015), probably due to differences in biomechanical demands and the magnitude of biting forces involved in food processing (Spencer, 2003). Our observed differential expression of EDJ morphology in hominin postcanine dentition related to tooth position could also, therefore, represent different influences.…”

Three‐Dimensional Geometric Morphometric Analysis of Treeshrew (Scandentia) Lower Molars: Insight into Dental Variation and Systematics

“…Geometric morphometric analysis of primate molars has contributed to the assessment of species‐level relationships within the order (e.g., Delgado et al, , , ; Gamarra et al, ). Many previous studies using geometric morphometrics have made use of two‐dimensional methods, capturing landmarks on photographs (White, ; Delgado et al, , , ; Gamarra et al, ). Although three‐dimensional methods require the use of unworn teeth, they have also been employed to effectively characterize variation (Skinner et al, , , ; Cooke, ; St. Clair and Boyer, ; Buser et al, ; Martin et al, ) and likely serve as a better means to interpret questions of phylogeny because more aspects of coronal morphology can be captured, such as relief (St. Clair and Boyer, ).…”

“…Geometric morphometric analysis of primate molars has contributed to the assessment of species-level relationships within the order (e.g., Delgado et al, 2014Delgado et al, , 2015Delgado et al, , 2016Gamarra et al, 2016). Many previous studies using geometric morphometrics have made use of two-dimensional methods, capturing landmarks on photographs (White, 2009;Delgado et al, 2014Delgado et al, , 2015Delgado et al, , 2016Gamarra et al, 2016). Although three-dimensional methods require the use of unworn teeth, they have also been employed to effectively characterize variation (Skinner et al, 2008(Skinner et al, , 2009b(Skinner et al, , 2009aCooke, 2011;St.…”

Diversidad morfológica mandibular de los monos capuchinos: un análisis morfométrico

“…J. DEL RIO ET AL./REV ARG ANTROP BIOL 20(2), 2018. doi:10.17139/raab.2018.0020.02.07 concuerdan con los obtenidos con técnicas de morfometría geométrica sobre los molares 1 y 2 de las mismas especies estudiadas en este trabajo y que han sido interpretados principalmente como cambios graduales a lo largo del proceso de divergencia filogenética, entre otros factores (NovaDelgado et al, 2015).Por otro lado, en nuestros resultados se puede observar que las especies de Cebus presentan una gran distribución en el CP1, extendiéndose principalmente en el extremo negativo, pero también en el positivo, y esto se observa también en los especímenes asignados a Sapajus(Fig. 2).…”