Dietary Inference from Upper and Lower Molar Morphology in Platyrrhine Primates

Abstract

The correlation between diet and dental topography is of importance to paleontologists seeking to diagnose ecological adaptations in extinct taxa. Although the subject is well represented in the literature, few studies directly compare methods or evaluate dietary signals conveyed by both upper and lower molars. Here, we address this gap in our knowledge by comparing the efficacy of three measures of functional morphology for classifying an ecologically diverse sample of thirteen medium- to large-bodied platyrrhines by diet category (e.g., folivore, frugivore, hard object feeder). We used Shearing Quotient (SQ), an index derived from linear measurements of molar cutting edges and two indices of crown surface topography, Occlusal Relief (OR) and Relief Index (RFI). Using SQ, OR, and RFI, individuals were then classified by dietary category using Discriminate Function Analysis. Both upper and lower molar variables produce high classification rates in assigning individuals to diet categories, but lower molars are consistently more successful. SQs yield the highest classification rates. RFI and OR generally perform above chance. Upper molar RFI has a success rate below the level of chance. Adding molar length enhances the discriminatory power for all variables. We conclude that upper molar SQs are useful for dietary reconstruction, especially when combined with body size information. Additionally, we find that among our sample of platyrrhines, SQ remains the strongest predictor of diet, while RFI is less useful at signaling dietary differences in absence of body size information. The study demonstrates new ways for inferring the diets of extinct platyrrhine primates when both upper and lower molars are available, or, for taxa known only from upper molars. The techniques are useful in reconstructing diet in stem representatives of anthropoid clade, who share key aspects of molar morphology with extant platyrrhines.

Smooth operator: The effects of different 3D mesh retriangulation protocols on the computation of Dirichlet normal energy

“…Developments in 3D scanning and image processing technologies over the past 15 years have enabled the digital reconstruction of tooth surface topography (Allen, Cooke, Gonzales, & Kay, ; Boyer, ; Ungar & Bunn, ; Ungar & M'Kirera, ; Ungar & Williamson, ; Winchester et al, ). When combined with new software tools for the analysis of surface topography and surface complexity, these approaches add a novel quantitative component to the study of occlusal surfaces.…”

“…Freedom from the constraints of identifying these landmarks allows more flexibility in contrasting tooth morphologies among disparate taxa. As with landmark‐based datasets, these new measures likely contain functional information about the masticatory performance of teeth, as evidenced by the systematic variation among species with different dietary habits, irrespective of taxonomic propinquity (Allen et al, ; Boyer, ; Bunn et al, ; Evans et al, ; Winchester et al, ). Implementation of these new measures relies on segmented 3D meshes of tooth crown surfaces, which—thanks in large part to online digital archives such as MorphoSource (Boyer, Gunnell, Kaufman, & McGeary, in press)—are becoming more widely available (see also Copes, Lucas, Thostenson, Hoekstra, & Boyer, ; Skinner, Kivell, Potze, & Hublin, ).…”

Introducing molaR: a New R Package for Quantitative Topographic Analysis of Teeth (and Other Topographic Surfaces)

“…Researchers interested in the form-function relationship of mammalian dentitions have begun supplementing traditional morphological measures with new metrics designed to reflect aspects of occlusal surface topography (e.g., Zuccotti et al 1998;M'Kirera and Ungar 2003;Evans et al 2007;Boyer 2008;Plyusnin et al 2008;Evans and Janis 2014;Winchester et al 2014;Allen et al 2015 Evans et al 2007). These metrics assess different aspects of dental surface topography over entire tooth crowns (or tooth rows) without requiring identification of homologous anatomic features or investigator-defined landmarks.…”

Ancestral resurrection of anthropoid estrogen receptor β demonstrates functional consequences of positive selection

“…Understandably, while there are several methods of measuring the different aspects of dental topography, when available, comparisons using both upper and lower molar morphologies provide a more accurate dietary inference than when just one of the two teeth is available (Allen et al, 2015). However, while hundreds of rodent fossils have been found in the same locale as Perupithecus , the discovery of the much smaller primate fossils is much less common and future fossil discoveries may change our view of early platyrrhine diet (Bond et al, 2015).…”