From outer to inner structural morphology in dental anthropology: integration of the third dimension in the visualization and quantitative analysis of fossil remains

Is the deciduous/permanent molar enamel thickness ratio a taxon-specific indicator in extant and extinct hominids?

“…As lateral enamel thickness topography has a profound effect on crown morphology, it is expected to bring a taxon-specific signature, even if likely diluted compared to that provided by total enamel thickness that includes occlusal enamel (e.g., Kono and Suwa, 2008;Macchiarelli et al, 2013;Suwa et al, 2009). To quantify lateral enamel, the bestfit plane across the cervicoenamel line was firstly set on each crown and the tooth material below this basal plane eliminated (Olejniczak et al, 2008a).…”

“…To quantify lateral enamel, the bestfit plane across the cervicoenamel line was firstly set on each crown and the tooth material below this basal plane eliminated (Olejniczak et al, 2008a). Then, a parallel plane to the former, tangent to the lowest enamel point of the occlusal basin, was defined and all material above it was also removed (Macchiarelli et al, 2013;Toussaint et al, 2010). Only the enamel and dentine portions between these two planes was preserved to estimate tissue proportions.…”

“…To visualize similarities vs. differences in enamel thickness topography within an assemblage of such variably sized and shaped teeth, ad hoc imaging techniques were used to virtually unroll lateral enamel and to project it into standardized morphometric maps Bondioli et al, 2010;Macchiarelli et al, 2013; for similar imaging techniques, see also Dowdeswell et al, 2017;Morita et al, 2016Morita et al, , 2017Puymerail, 2011;Puymerail et al, 2012aPuymerail et al, , 2012bTsegai et al, 2017). Because each morphometric map (MM) is scaled according to the maximal value of the analysed tooth, the patterns expressed by the dm2s and the M1s are independent from the absolute and relative enamel thickness values.…”

“…Martin for measurement procedure and standardization (Martin, 1985), the bi-three-dimensional assessment of tooth enamel thickness has become routine in taxonomic and adaptive/evolutionary studies of fossil and extant primates (e.g., Alba et al, 2013;Kono, 2004;Kono et al, 2014;Macchiarelli et al, 2004Macchiarelli et al, , 2009Macchiarelli et al, , 2013Olejniczak et al, 2008aOlejniczak et al, , 2008bOlejniczak et al, , 2008cOlejniczak et al, , 2008dPan et al, 2016;Skinner et al, 2015;Smith et al, 2003Smith et al, , 2005Smith et al, , 2011Smith et al, , 2012Suwa et al, 2009;Zanolli et al, 2015Zanolli et al, , 2016a. Commonly used to infer durophagy and considered as a proxy of the dietary niches exploited by extinct species (e.g., Constantino et al, 2011Constantino et al, , 2012Lucas et al, 2008;Martin et al, 2003;Schwartz, 2000a;Teaford, 2007;Teaford and Ungar, 2015;Vogel et al, 2008), occlusal enamel thickness is seen as intimately related to dietary abrasiveness and selectively responsive to lifetime dental wear resistance (Pampush et al, 2013;Rabenold and Pearson, 2011).…”

“…Most studies on enamel thickness have primarily considered the permanent teeth, especially the molar series, while the extent of covariation in tooth enamel thickness between deciduous and permanent counterparts has been the object of limited quantitative analyses, including in hominids (for a recent synthesis and review of studies on deciduous enamel thickness in humans, see table 1 in Mahoney, 2013; additionally, among other contributions, see Benazzi et al, 2011;Fornai et al, 2014Fornai et al, , 2016Macchiarelli et al, 2006Macchiarelli et al, , 2013Peretto et al, 2015;Zanolli, 2015a;Zanolli et al, 2010aZanolli et al, , 2012Zanolli et al, , 2014. Accordingly, quantitative support to answer a number of questions remains so far elusive.…”