Rapid dental development in a Middle Paleolithic Belgian Neanderthal

Abstract

The evolution of life history (pace of growth and reproduction) was crucial to ancient hominin adaptations. The study of dental development facilitates assessment of growth and development in fossil hominins with greater precision than other skeletal analyses. During tooth formation, biological rhythms manifest in enamel and dentine, creating a permanent record of growth rate and duration. Quantification of these internal and external incremental features yields developmental benchmarks, including ages at crown completion, tooth eruption, and root completion. Molar eruption is correlated with other aspects of life history. Recent evidence for developmental differences between modern humans and Neanderthals remains ambiguous. By measuring tooth formation in the entire dentition of a juvenile Neanderthal from Scladina, Belgium, we show that most teeth formed over a shorter time than in modern humans and that dental initiation and eruption were relatively advanced. By registering manifestations of stress across the dentition, we are able to present a precise chronology of Neanderthal dental development that differs from modern humans. At 8 years of age at death, this juvenile displays a degree of development comparable with modern human children who are several years older. We suggest that age at death in juvenile Neanderthals should not be assessed by comparison with modern human standards, particularly those derived from populations of European origin. Moreover, evidence from the Scladina juvenile and other similarly aged hominins suggests that a prolonged childhood and slow life history are unique to Homo sapiens.

Fig. 1.

Developmental stress matched across the anterior dentition of the Scladina juvenile (gold-coated casts). (A–C) Maxillary dentition: central incisor (A), lateral incisor (B), and canine (C). (D–F) Mandibular dentition: central incisor (D), lateral incisor (E), and canine (F). The first stress event (blue arrow) was identified in the histological section of the upper first molar at 2.4 years of age, with the number of subsequent perikymata after this event indicated on each tooth. The number of periradicular bands between the cervix and subsequent stress event (green arrow) is indicated, with an average of 113 lines between events (904 days). Thus, this second event occurred at 4.9 years of age.

Fig. 2.

Developmental chronology of the Scladina juvenile illustrating crown formation (gray) and root formation (black). The positions of two stress events used to register teeth (see Fig. 1 and SI Fig. 4) are indicated (dotted vertical lines), as is death (solid vertical line). Given that the upper lateral incisor and first molar had completed root formation before death, it was not possible to determine the end of root formation (indicated by question marks).

Fig. 3.

Comparison of the degree of development in the similarly aged fossil juveniles. (A) From Jebel Irhoud (33). (B) From Scladina (right mandible mirrored for comparison). Note the absence of the second molar in the early H. sapiens juvenile and the advanced stage of second molar eruption in the Neanderthal from Scladina.