Uniform, circular, and shallow enamel pitting in hominins: Prevalence, morphological associations, and potential taxonomic significance.

This study explores a particular form of enamel pitting originally identified in Paranthropus robustus. We call this uniform, circular, and shallow (UCS) pitting to distinguish it from more irregular and nonuniform defects often associated with enamel hypoplasia. We pose the hypothesis that UCS pitting is unique to the genus Paranthropus. We test this by investigating hominin dental remains from the ca. 3.4 Ma to ca. 1.1 Ma fossiliferous sequence at Omo, Ethiopia (n = 76) to look for evidence of UCS pitting in an assemblage that includes at least three hominin genera (Australopithecus, Paranthropus, and Homo). We also examine the correlation between UCS pitting, tooth size, enamel thickness, and cusp proportions in samples from both eastern Africa (Omo) and southern Africa (Drimolen Main Quarry ∼2.04-1.95 Ma, Swartkrans ∼1.9-1.4 Ma, and Kromdraai ∼1.95-1.78 Ma). In the Omo specimens, we found UCS pitting similar to that seen in P. robustus. While we observed this pitting on five of 24 permanent teeth and two deciduous molars from both Paranthropus aethiopicus and Paranthropus boisei, we also identified UCS pitting on five of 13 non-Paranthropus hominin permanent posterior teeth from Member B (∼3.0 Ma). Our correlation studies yielded no association between the presence of UCS pitting and variation in tooth size, enamel thickness, or cusp proportions. The consistent appearance and characteristics of UCS pitting suggest a shared etiology. Our findings also suggest that UCS pitting may result from a genetic effect related to enamel formation, potentially in association with specific environmental or dietary factors.