We report here revised chronological ages at death of immature fossil hominids demonstrating for the first time that Plio-Pleistocene hominids had markedly abbreviated growth periods relative to modern man, similar to those of the modern great apes. Previous estimates of age at death for fossil hominids have principally been based on dental eruption, maturation and dental wear criteria for modern man and hence reflect their age in 'human' years. We are now able to estimate the absolute duration of permanent incisor crown formation by observing gross incremental growth features in enamel and thereby apply a timescale to dental developmental events for specimens representing four Plio-Pleistocene fossil hominid taxa. Thus we have derived more reliable-species-specific-estimates of age at death that provide a more secure model on which to base studies of the palaeodemography, growth and maturation of early hominids.
Growth and development are both fundamental components of demographic structure and life history strategy. Together with information about developmental timing they ultimately contribute to a better understanding of Neanderthal extinction. Primate molar tooth development tracks the pace of life history evolution most closely, and tooth histology reveals a record of birth as well as the timing of crown and root growth. High-resolution micro-computed tomography now allows us to image complex structures and uncover subtle differences in adult tooth morphology that are determined early in embryonic development. Here we show that the timing of molar crown and root completion in Neanderthals matches those known for modern humans but that a more complex enamel-dentine junction morphology and a late peak in root extension rate sets them apart. Previous predictions about Neanderthal growth, based only on anterior tooth surfaces, were necessarily speculative. These data are the first on internal molar microstructure; they firmly place key Neanderthal life history variables within those known for modern humans.
On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth.
Adult mandibles of 317 modern humans and 91 great apes were selected that showed no pathology. Adult mandibles of Pan troglodytes troglodytes, Pongo pygmaeus pygmaeus and Gorilla gorilla gorilla and from 2 modern human populations (Zulu and Europeans from Spitalfields) were reliably sexed. Thirteen measurements were defined and included mandibular height, length and breadth in representative positions. Univariate statistical techniques and multivariate (principal component analysis and discriminant analysis) statistical techniques were used to investigate interspecific variability and sexual dimorphism in human and great ape mandibles, and intraspecific variability among the modern human mandibles. Analysis of interspecific differences revealed some pairs of variables with a tight linear relationship and others where Homo and the great apes pulled apart from one another due to shape differences. Homo and Pan are least sexually dimorphic in the mandible, Pan less so than Homo sapiens, but both the magnitude of sexual dimorphism and the distribution of sexually dimorphic measurements varied both among and between modern humans and great apes. Intraspecific variation among the 10 populations of modern humans was less than that generally reported in studies of crania (74.3 % of mandibles were correctly classified into 1 of 10 populations using discriminant functions based on 13 variables as compared with 93 % of crania from 17 populations based on 70 variables in one extensive study of crania). A subrecent European population (Poundbury) emerged as more different from a recent European population (Spitalfields) than other more diverse modern populations were from each other, suggesting considerable morphological plasticity in the mandible through time. This study forms a sound basis on which to explore mandibular variation in Neanderthals, early Homo sapiens and other more ancient fossil hominids.Key words : Hominoids ; mandible ; sexual dimorphism. In recent years, a number of important fossil mandibles attributed to both Neanderthals and early Homo sapiens have been recovered. At the same time debate about human evolution has come to focus more sharply on the origins of modern Homo sapiens. Potentially, fossil mandibles such as those, for example, from Heidelberg in Germany, Klasies River Mouth in South Africa, and those from Tabun, Kebara, and Qafzeh in Israel, which differ considerably in their size and morphology, may help shed light on this key issue. However Neither is it clear how certain fundamental mandibular dimensions such as height, breadth and length, relate to mandibular size and to each other and to what extent apparently contrasting mandibular morphologies may simply be a consequence of body size and sexual dimorphism. Despite the fact the mandible is better represented in the the hominid and hominoid fossil record than most other bones there are still many more comparative studies of the cranium than there are of the mandible.To explore these issues we have undertaken a
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.