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

In Primates, enamel thickness variation stems from an evolutionary interplay between functional/adaptive constraints (ecology) and the strict control mechanisms of the morphogenetic program. Most studies on primate enamel thickness have primarily considered the permanent teeth, while the extent of covariation in tooth enamel thickness distribution between deciduous and permanent counterparts remains poorly investigated. In this test study on nine extant and fossil hominids we investigated the degree of covariation in enamel proportions between 25 pairs of mandibular dm2 and M1 by a so-called “lateral enamel thickness diphyodontic index”. The results did not provide an unambiguous picture, but rather suggest complex patterns likely resulting from the influence of many interactive factors. Future research should test the congruence of the “diphyodontic signal” between the anterior and the postcanine dentition, as well as between enamel and the enamel-dentine junction topography.