How Neandertal molar teeth grew

Laboratoire de Géobiologie, Biochronologie et Paléontologie Humaine, UMR 6046 CNRS, Université de Poitiers, 86022 Poitiers, France.
Nature (Impact Factor: 41.46). 01/2007; 444(7120):748-51. DOI: 10.1038/nature05314
Source: PubMed


Growth and development are both fundamental components of demographic structure and life history strategy. Together with information about developmental timing they ultimately contribute to a better understanding of Neanderthal extinction. Primate molar tooth development tracks the pace of life history evolution most closely, and tooth histology reveals a record of birth as well as the timing of crown and root growth. High-resolution micro-computed tomography now allows us to image complex structures and uncover subtle differences in adult tooth morphology that are determined early in embryonic development. Here we show that the timing of molar crown and root completion in Neanderthals matches those known for modern humans but that a more complex enamel-dentine junction morphology and a late peak in root extension rate sets them apart. Previous predictions about Neanderthal growth, based only on anterior tooth surfaces, were necessarily speculative. These data are the first on internal molar microstructure; they firmly place key Neanderthal life history variables within those known for modern humans.

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    • "The scale-free 3D relative enamel thickness (3D RET) was computed following Olejniczak et al. (2008a,b,c); (see also, Kono, 2004; Macchiarelli et al., 2006). For the LM3 of IGF4351, the worn enamel apex and dentine horn of the protoconid and the enamel apex of the metaconid were virtually reconstructed for 2D RET using as a reference model the outline of the nearly unworn LM3 FS1996#Fi97 (Fig. 1A), thus allowing a more realistic assessment of its RET value (cf. "
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    Comptes Rendus Palevol 06/2015; DOI:10.1016/j.crpv.2015.02.001 · 1.19 Impact Factor
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    • "We investigated two components of enamel microstructure of the Moula-Guercy remains: perikymata and linear enamel hypoplasia. Perikymata are enamel surface manifestations of internal growth increments known as striae of Retzius (Hillson, 1996) representing 7 or 8 days' worth of enamel growth in Neanderthals (Macchiarelli et al., 2006; Smith et al., 2009; Smith et al., 2010). Perikymata cover the surface of lateral enamel, forming shallow grooves or waves approximately 100 lm apart (Hillson and Bond, 1997). "
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    • "The neonatal line is an accentuated marking created at birth and retained within enamel (Rushton, 1933). The marking can temporarily reduce secretion rates (e.g., Macchiarelli et al., 2006). "
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    ABSTRACT: Correlation between the timing of permanent first molar eruption and weaning age in extant primates has provided a way to infer a life history event in fossil species, but recent debate has questioned whether the same link is present in human infants. Deciduous incisors erupt at an age when breast milk can be supplemented with additional foods (mixed feeding), and weaning is typically complete before permanent first molars erupt. Here, I use histological methods to calculate the prenatal rate by which enamel increases in thickness and height on human deciduous incisors, canines, and molars (n = 125). Growth trajectories for each tooth type are related to the trimesters and assessed against the eruption sequence and final crown height. Analyses show that central incisors initiate early in the second trimester with significantly faster secretion rates relative to canines and second molars, which initiate closer to birth. Even though initial extension rates were correlated with crown height and scaled with positive allometry within each tooth class, the relatively short incisors still increased in height at a significantly faster rate than the taller canines and molars. The incisor prenatal "fast track" produces a greater proportion of the crown before birth than all other tooth types. This growth mechanism likely facilitates early incisor eruption at a time when the mixed feeding of infants can be initiated as part of the weaning process. Findings provide a basis from which to explore new links between developmental trends along the tooth row and mixed feeding age in other primates. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.
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