Histological reconstruction of dental development and age at death in a juvenile gibbon (Hylobates lar).

Although research on dental development in great apes and modern humans has provided comparative models for life history, growth and development in hominin evolution, almost nothing is known about dental development in their sister group, the hylobatids. Hylobatids are of interest because they differ in important life history variables from other catarrhines of similar body mass, and can help to provide more general models for the factors underlying patterns of dental development. This study uses histological techniques to reconstruct developmental sequence, crown formation times, root extension rates, daily rates of enamel and dentine formation, and age at death in a single specimen of Hylobates lar. Thin sections were prepared of permanent mandibular teeth and analyzed by polarized light microscopy. Age at death was determined to be 2.88 yrs calibrated from a pattern of accentuated growth increments. At this age, permanent teeth in occlusion include I1, I2, and M1. Developing permanent teeth include C1, P3, P4, and M2. P3 lags behind P4 in development, and there is no indication of M3 present in the crypt. Differences between the gibbon specimen and great apes include greater prenatal development of M1, accelerated incisor development relative to molars and prenatal development of I1, no overlap between M2 and M3 crown development, shorter crown formation times, and slower root extension rates of 4-5 micron daily in the molars. Root extension rates are higher in the incisors. The periodicity of growth increments is four days, more similar to macaques than to other hominoids. Daily formation rates for enamel of 1.2-4.9 micron and dentine of 1.7-4.9 micron are similar to those reported for other catarrhines.