Extension rates and growth in tooth height of modern human and fossil hominin canines and molars.
The aim of this study was to describe similarities and differences in the way modern and fossil hominin teeth grow in height. Measurements from longitudinal ground sections of 7 modern human canines and 19 first permanent molars were used to calculate extension rates in the crowns and roots and to plot distance curves for growth in tooth height. These were compared with identical data for 3 fossil hominin teeth attributed respectively to Paranthropus robustus, Homo erectus and Homo neanderthalensis. Enamel extension rates in each of the three fossil taxa fell within the range of modern humans. Root extension rates in the fossil taxa also fell within modern human ranges but differed in their pattern with either an early or late marked increase in root length. Extension rates in the canine crowns were higher in cuspal enamel than in lateral enamel. Combinations of high or low cuspal enamel extension rates, with either longer or shorter times taken to form lateral enamel, explain how crown formation times may vary independently of completed crown heights.