A new approach to quantify enamel thickness distribution and the enamel-dentine junction topography in primate teeth
Résumé
Dental inner structural organization is a key diagnostic element for assessing fossil primate
taxa. It is now recognized that throughout hominid evolution, and especially in Homo, enamel
thickness (ET) varied quickly and repeatedly, thus more closely reverberating
microevolutionary fluctuations. In contrast, the more stable and conservative underlying
dentine, more accurately reflects macroevolutionary changes. In fact, while ET is generally
considered an indicator of taxonomic affinities, it varies with respect to a number of bio-
ecological determinants, such as life span, sexual dimorphism, and of course dietary habits.
However, the prevalent signal of enamel (i.e., taxonomic vs. functional) remains uncertain.
Conversely, the enamel-dentine junction (EDJ) is a reliable proxy to discriminate hominid taxa,
even at sub-specific level. In dental (paleo)anthropology, ET and EDJ are routinely assessed
separately, characterizing the former using "average" estimates (such as the relative ET index)
and qualitative evaluation of its distribution cartographies, and the latter by advanced
morphometric methods. Here we introduce an original surface matching-based approach to
quantify and statistically compare chromatic cartographies representing ET distribution and the
EDJ shape. We applied this method to a limited set of unworn maxillary and mandibular M1s
(N=39) representing the extant hominids. By using PCA and between-group PCA, we
distinguish the four great ape taxa either for the ET or EDJ maps. When the results from both
tooth tissues are combined, even if some taxa overlap, a taxonomic signal is still detectable.
This exploratory study highlights the promising prospects of this method, notably to investigate
the primate fossil record.
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