Three-dimensional enamel thickness of the fourth deciduous premolars in Middle-to-Late Pleistocene Pongo
Received date: 2025-06-20
Revised date: 2025-10-13
Online published: 2026-04-17
Enamel thickness holds significant implications for studies on primate phylogenetic evolution and dietary adaptations. Previous studies have systematically explored the enamel thickness of permanent teeth in great apes (e.g., Pongo, Gorilla, and Pan), whereas research on deciduous teeth enamel thickness remains relatively limited. Although a recent work has reported two-dimensional (2D) enamel thickness measurements of fossil Pongo deciduous premolars, their three-dimensional (3D) enamel thickness characteristics remain unclear. High-resolution micro-CT data (voxel size: 15.82~23.42 μm) was employed here to conduct a quantitative analysis of the 3D enamel thickness in 16 Middle-to-Late Pleistocene Pongo fourth deciduous premolars (dP4) from Guangxi, consisting of 7 dP4s and 9 dP4s. The enamel thickness results of fossil Pongo were compared with that of human taxa (Java Homo erectus, Middle Pleistocene hominin, Neanderthals, and modern humans) and extant Pongo. Results show that the three enamel thickness indices of dP4 are greater than those of dP4. Specifically, the mean values of 3DAET, 3DRET, and 3DRED for dP4 are 0.62 mm (0.54~0.78 mm), 9.74 (8.04~12.92), and 7.62 (7.11~8.35), respectively. The corresponding values for dP4 are 0.51 mm (0.44~0.65 mm), 7.94 (6.54~10.27), and 7.16 (6.68~7.95), respectively. Statistical analyses also reveal that fossil Pongo exhibits significantly thicker enamel in dP4 than in dP4 (p<0.05). This significant difference is primarily due to the significantly greater enamel volume in dP4 compared to dP4 (p=0.03), whereas it shows no significant correlation with the differences in the enamel-dentine junction area (p=0.92) or dentine volume (p=0.68). Furthermore, according to the 3DRET results, the fossil Pongo dP4 can be classified as having thin enamel, whereas the dP4 falls into the category of hyper-thin enamel. For comparison, the dP4 enamel thickness in human taxa can be classified into various categories, ranging from thin to intermediate thick. Therefore, the 3D enamel thickness of the fossil Pongo dP4 is generally thinner than that of human taxa, which is consistent with the findings in permanent teeth. Finally, the mean 3DAET and mean 3DRET of the extant Pongo dP4 are 0.41 mm and 7.51, respectively, both of which are lower than the corresponding values in fossil Pongo. While Middle-to-Late Pleistocene Pongo dP4s may exhibit thicker enamel than their extant counterparts, this hypothesis requires further validation with additional data from extant Pongo. The primary data provided in this study are expected to lay a foundation for future comparative researches on 3D enamel thickness in hominid deciduous teeth.
Key words： Fossil Pongo; deciduous premolars; 3D enamel thickness; South China
YI Zhixing , QIU Ruoxuan , WANG Wei , LIAO Wei , LIANG Hua , TIAN Chun , MIERADILI · Tuerxunjiang , ZHANG Yijing , YAO Yanyan . Three-dimensional enamel thickness of the fourth deciduous premolars in Middle-to-Late Pleistocene Pongo[J]. Acta Anthropologica Sinica, 2026 , 45(02) : 248 -257 . DOI: 10.16359/j.1000-3193/AAS.2025.0116
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