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Molar development in common chimpanzees (Pan troglodytes).
T M Smith1, D J Reid, M C Dean
1Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany. tsmith@eva.mpg.de
Journal of Human Evolution
|November 7, 2006
Summary
This study redefines chimpanzee molar growth standards, revealing significant variation in enamel formation time and eruption rates. Understanding this developmental variation is crucial for interpreting fossil hominoid dental evidence.
Area of Science:
- Paleoanthropology
- Primate Dental Development
- Biochronology
Background:
- Limited understanding of intraspecific variation in hominoid molar incremental features.
- Previous histological studies suggested an unlikely short interval between chimpanzee molar crown completion and eruption.
Purpose of the Study:
- To redefine growth standards for chimpanzee molar teeth.
- To examine variation in incremental features like Retzius lines and enamel thickness.
- To establish accurate formation and extension rates for chimpanzee molar development.
Main Methods:
- Histological analysis of a large sample of chimpanzee molars.
- Determination of Retzius line periodicity.
- Measurement of cuspal enamel thickness and daily secretion rates.
- Analysis of cuspal initiation and completion sequences.
- Calculation of coronal and root extension rates.
Main Results:
- Retzius line periodicity established at 6 or 7 days.
- Significant variation found in cuspal enamel thickness and molar formation times (2-3 years).
- Daily enamel secretion rates varied from 3-5 microns/day (inner to outer enamel).
- Coronal and root extension rates showed variation by molar type and jaw (M1 > M2/M3; mandibular > maxillary).
Conclusions:
- Chimpanzee molar development exhibits considerable intraspecific variation.
- Established growth standards provide a more accurate baseline for comparative studies.
- Developmental variation must be considered when interpreting fossil hominoid dental samples.
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