Enamel hypoplasia in the deciduous teeth of early Miocene catarrhines: evidence of perinatal physiological stress

Abstract

Enamel hypoplasia (EH) is a deficiency in enamel thickness due to physiological insults that compromise ameloblast function during the secretory phase of amelogenesis. The prevalence of EH in the deciduous teeth of nonhuman primates is largely unknown. One exception is the recent discovery of EH in the deciduous teeth of extant great apes which exhibit significant differences in prevalence between genera (Lukacs, 1999 a, 2000 a, Am. J. phys. Anthrop.110, 351–363). EH in deciduous teeth of other primates, living and fossil, remain undocumented. This communication describes a “plane form'’ type of EH known as localized hypoplasia of primary canines (LHPC) (Skinner, 1986 a,Am. J. phys. Anthrop.69 , 59–69) in early Miocene catarrhines from Kenya. Specimens were examined macroscopically, with a 10× hand lens and with a variable power (10–30×) binocular microscope. Fédération Dentaire International (FDI)/Defects of Dental Enamel (DDE) standards were employed in recognition and recording of enamel defects (Fédération Dentaire International, 1982, Int. Dent. J.32, 159–167; Clarkson, 1989, Adv. Dental Res.3, 104–109). Size, shape and location of defects were measured and recorded on an outline drawing of the tooth crown. The Kenya National Museum study sample includes six genera of early Miocene catarrhines (n=66 specimens, with n=80 teeth). Seven deciduous teeth were afflicted with EH, yielding an overall prevalence of 8·75%. Two taxa, Kalepithecus (n=1 deciduous canine) and Proconsul (n=3 deciduous canines), were affected with LHPC. Expression of LHPC in fossil catarrhines is consistent with the expression of EH observed in skeletal samples of extant great apes. This report establishes an ∼17–23Ma antiquity for EH among early catarrhines and suggests that the neonatal stage of ontogenetic development was sufficiently stressful physiologically to produce disruption in amelogenesis. These physiological stresses impacted neonates of fossil taxa with a wide range of adult body sizes, from large-bodied Proconsul major (∼75kg) to one of the smaller-bodied catarrhines, Kalepithecus (∼5kg).