Variation in daily enamel increments in fossil hominins

Fossil teeth contain a longitudinal record of their growth in the form of incremental layers or markings of different time scales. Objective: We have measured daily incremental markings or cross striations in enamel in the largest sample of Plio-Pleistocene hominin specimens studied so far. Methods: We used portable confocal scanning optical microscopy on natural tooth fractures, and polarized light microscopy on ground sections. Results: Our results indicate that there is marked variation in daily growth rates across hominins within this temporal period. Conclusion: As in modern humans and other primates, daily rates increased from inner to outer enamel and decreased towards cervical end of the tooth. We also compared the megadontia quotient, which is indicative of relative tooth size in relation to body size, with daily rates. Our results show that taxa with the larger tooth size also display higher daily rates of enamel growth. High secretion rates are in keeping with the need to maintain total crown formations times within the constraints of the growth period.