Figure 6

Diagrammatic representations of a P. robustus M3, based on SK 835, showing successive ¼ fraction stages of time between crown initiation (Ci) and root completion (RC) as well as ¼ fraction stages of crown height and root height. Either stages of time fractions or of height fractions can be matched to any developing hominin M3, which ever fits best, and to the formation time estimated for SK 835 (given here in years). Adding a 3-year range (from 4 to 7 years) for M3 initiation times to the age given for any fractional stage provides a range of chronological ages for dental development that, although wide, may bracket the undoubted variation there would be in M3 growth and development generally. Supplementary Table S4 lists 21 Plio-Pleistocene hominins with incomplete M3s. Note that crown completion (CC) and root completion (RC) are identical in both formation stage sequences.