Phylogenetic Influences on Tooth Mineral Density in Primates

Abstract

In primates, the size of teeth at birth is inversely related to body size. Here, we test the hypothesis that dental mineralization follows this same pattern. Forty-eight newborn primates were microCT scanned at a resolution of 20.5 μm. From the scans, grayscale intensity was converted to hydroxyapatite (HA) density (mg HA/cm3) using a linear conversion of grayscale values to calibration standards of known HA density (R2=0.99). Using Amira software, mineralized dental tissues were captured by segmenting the tooth cusps first, and then capturing the remainder of the teeth at descending thresholds of gray levels. Correlations and regression analyses were used to assess the relationship of HA density to cranial length, a proxy for head size. Results reveal that in strepsirrhines (lemurs and lorises), peak HA density of the first permanent molar (M1) negatively correlates with cranial length. In contrast, the HA density of M1 positively correlates with cranial length in monkeys. This supports the hypothesis that natural selection acts independently on dental growth as opposed to mineralization, and indicates clear phylogenetic differences among primates. Other phylogenetic differences relate to the location of peak dental HA density. In monkeys, anterior teeth are more mineralized than postcanine teeth. In most strepsirrhines, postcanine teeth are the most highly mineralized. In addition, mineralization was highly localized to the cusp in strepsirrhines, while in monkeys the mineralization is more widespread, including the basins of deciduous teeth. These findings suggest that monkeys have a more prolonged process of dental mineralization that begins with non-grinding teeth, while mineralization of postcanine teeth, especially M1, is delayed until after birth. This may in part be a result of relatively later weaning in anthropoid primates. Support or Funding InformationNSF # BCS-1231717, NSF # BCS-1231350, NSF # BCS-0958438 Peak hydroxyapatite (HA) density of postcanine deciduous teeth and the first permanent molar (M1) in newborn primates.