Further morphological evidence on South African earliest Homo lower postcanine dentition: Enamel thickness and enamel dentine junction

Abstract

The appearance of the earliest members of the genus Homo in South Africa represents a key event in human evolution. Although enamel thickness and enamel dentine junction (EDJ) morphology preserve important information about hominin systematics and dietary adaptation, these features have not been sufficiently studied with regard to early Homo. We used micro-CT to compare enamel thickness and EDJ morphology among the mandibular postcanine dentitions of South African early hominins (N = 30) and extant Homo sapiens (N = 26), with special reference to early members of the genus Homo. We found that South African early Homo shows a similar enamel thickness distribution pattern to modern humans, although three-dimensional average and relative enamel thicknesses do not distinguish australopiths, early Homo, and modern humans particularly well. Based on enamel thickness distributions, our study suggests that a dietary shift occurred between australopiths and the origin of the Homo lineage. We also observed that South African early Homo postcanine EDJ combined primitive traits seen in australopith molars with derived features observed in modern human premolars. Our results confirm that some dental morphological patterns in later Homo actually occurred early in the Homo lineage, and highlight the taxonomic value of premolar EDJ morphology in hominin species.

Intra‐individual metameric variation expressed at the enamel‐dentine junction of lower post‐canine dentition of South African fossil hominins and modern humans

“…Moreover, as revealed by our bivariate plots, modern human M 3 s show a large scale of shape variability. This is consistent with previous observations using conventional tools (Garn, Lewis, & Kerewsky, ; Townsend, Richards, & Hughes, ) or geometric morphometrics (Morita et al, ; Pan et al, ). It has been suggested that in modern humans, the inter‐individual differences are larger for the M 2 s than for the M 1 s (Braga et al, ).…”

Late Pleistocene hominin teeth from Laoya Cave, southern China

“…The AET3D of LYC1 (Table 5) falls within the range of variation for both Neanderthals and recent H. sapiens (values from Pan et al (2016)). The value of LYC1 is higher than the mean value of Neanderthals provided in Olejniczak et al (2008).…”

“…Overall, the thickest enamel falls around the buccal groove in the occlusal aspect of the buccal surface. M 3 s of recent modern humans show a similar pattern (see also SI Figure 4 in Pan et al (2016)), with the buccal surface being thicker than the lingual aspect. Typically, the occlusal third of the hypoconid's buccal surface has thick, evenly distributed enamel in recent H. sapiens; however, it is the mesial aspect of the hypoconid that shows the thicker enamel in LYC1.…”

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

“…The existence of interspecific differences in molar enamel thickness has been ascertained within the australopith clade (e.g., Grine and Daegling, 2017;Grine and Martin, 1988;Olejniczak et al, 2008b;Pan et al, 2016;Skinner et al, 2015), but their consideration here is far beyond the specific purposes of our present work. Details about the composition and origin of the mandibular dm2 and M1 specimens/samples are provided in Table 1.…”

“…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).…”