The Developing Dentition and Tooth Structure in Hominoids

An understanding of the patterns of maturation that characterize earlier hominines would markedly increase our understanding of human evolution. Earlier reports suggesting that the australopithecines had a pattern of growth and development similar to that of modern humans have been challenged in recent years by a variety of studies. These studies have focused on dental enamel microstructure in attempts to characterize the time frame of enamel calcification. When the latter are combined with data on root development and the sequence of dental calcification and eruption, a picture emerges that attempts to characterize modern human, early hominine,l and ape dental maturation.One of the major features that distinguish modern humans from other hominoids is the increased length of the childhood dependency period. Many writers have looked at this time as an important element in the basic adaptive strategy of humans (Gould, 1976;Dobzhansky, 1962;Mann, 1972;Lovejoy, 1981). A prolonged dependency period provides time for the transmission of complex information about the environment, its resources, and the methods of resource procurement from one generation to another. A lengthened time of dependency can permit the young to internalize information about a number of different, seasonally exploited habitats and the techniques most useful in finding and harvesting the resources in each area. Prolonged dependency also provides time for the young to learn the cues underlying the successful employment of the vast repertoire o f social hehaviorq that govern the peaceful and harmonious interactions of members of a society. It is possible that even the development of language is founded on the lengthened learning period of childhood.The precise biological mechanisms that were modified in the course of human evolution to bring about the prolongation of the dependency period are unknown, although Gould (1976) suggests that a relatively small number of changes in the regulatory genes controlling ontogenetic processes would be all that was necessary. Holloway (1969) has argued that the adaptive value of a prolonged time of maturation need not be directly related to an increase in brain size. In this view, an enlarged parietal association cortex, which he has described in early hominine endocasts (Holloway, 1981(Holloway, , 1983(Holloway, , 1984(Holloway, , 1985 Holloway and Kimbel, 1986; but see 'In this paper, we follow Weiss (1987) and Weiss and Mann (1990) in employing the subfamily IIomininae, rather than the family Hominidae, to describe humans and our close immediate ancestors and relatives. 0 1990 Wiley-Liss, Inc. PHYSICAL, ANTHROPOI,OGY lV0l 33,1990 Falk, 1987, for a contrasting view), would provide the essential neurological foundation for an extended childhood dependency to evolve. An understanding of when the prolonged childhood dependency period appeared in hominine evolution would be extremely useful for our comprehension of human evolution. In 1948 Dart initially suggested that the South African australop...

Section: Striae Of Retziusmentioning

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Section: Appraisal Of Crown-formation Times and Developmental Inferementioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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See 3 more Smart Citations

Patterns of ontogeny in human evolution: Evidence from dental development

Mann

Lampl

Monge

1990

Longitudinal study of dental development in chimpanzees of known chronological age: Implications for understanding the age at death of Plio-Pleistocene hominids

Anemone

Mooney

Siegel

1996

107

Reconstruction of life history variables of fossil hominids on the basis of dental development requires understanding of and comparison with the pattern and timing of dental development among both living humans and pongids. Whether dental development among living apes or humans provides a better model for comparison with that of Plio-Pleistocene hominids of the genus Australopithecus remains a contentious point. This paper presents new data on chimpanzees documenting developmental differences in the dentitions of modern humans and apes and discusses their significance in light of recent controversies over the human or pongid nature of australopithecine dental development. Longitudinal analysis of 299 lateral head radiographs from 33 lab-reared chimpanzees (Pan troglodytes) of known chronological age allows estimation of means and standard deviations for the age at first appearance of 8 developmental stages in the mandibular molar dentition. Results are compared with published studies of dental development among apes and with published standards for humans. Chimpanzees are distinctly different from humans in two important aspects of dental development. Relative to humans, chimpanzees show advanced molar development vis a vis anterior tooth development, and chimpanzees are characterized by temporal overlap in the calcification of adjacent molar crowns, while humans show moderate to long temporal gaps between the calcification of adjacent molar crowns. In combination with recent work on enamel incremental markers and CAT scans of developing dentitions of Plio-Pleistocene hominids, this evidence supports an interpretation of a rapid, essentially "apelike" ontogeny among australopithecines.

Permanent tooth calcification in chimpanzees (Pan troglodytes): Patterns and polymorphisms

Kuykendall

Conroy

1996

Tooth calcification is an important developmental marker for use in constructing models for early hominid life history, particularly for its application to the fossil record. As chimpanzees are commonly utilized in interspecific comparisons in such research, this study aims to improve available baseline data for tooth calcification patterns in chimpanzees (Pan troglodytes), and to quantify basic patterns and polymorphisms. We present an analysis of developmental patterns for the left mandibular dentition (I1-M3) based on intraoral radiographs obtained from a cross-sectional sample of chimpanzees (58 males, 60 females) housed at LEMSIP (NYU Medical Center) and Yerkes (Emory University). No significant differences with previous descriptions of the basic sequences of tooth calcification in chimpanzees were found, but variation in such patterns was documented for the first time. In the overall sequence, polymorphisms between the canine and the group (M2 P4 P3) reached significant levels. This is due to the relative delay in canine crown formation compared to other teeth. Differences in the basic sequence between males and females were recorded, but are due to minor shifts in the percentages of occurrence for polymorphic sequences which are common to both genders. Perhaps our most important findings are that a) different polymorphic sequences occur in tooth calcification and tooth emergence in chimpanzees, and b) developmental relationships among teeth fluctuate throughout tooth calcification. Thus, characterizations of dental developmental patterns based on particular stages of development cannot necessarily be extrapolated to other stages without supporting data.