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Evolution of anthropoid jaw loading and kinematic patterns.
M J Ravosa1, C J Vinyard, M Gagnon
1Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611-3008, USA. m-ravosa@nwu.edu
American Journal of Physical Anthropology
|August 5, 2000
Summary
Crown anthropoids evolved distinct jaw structures, featuring longer ascending rami and higher jaw joints compared to strepsirhines. These adaptations support unique masticatory patterns crucial for their evolutionary success.
Area of Science:
- Primate Paleontology
- Comparative Anatomy
- Biomechanics
Background:
- Primate evolution involved significant changes in skull and masticatory systems, particularly in crown anthropoids.
- Understanding mandibular loading and kinematic patterns offers insight into phylogenetic and adaptive pathways.
Purpose of the Study:
- To perform allometric analyses of masticatory function parameters in strepsirhines and anthropoids.
- To compare mandibular and cranial morphology between these primate groups.
- To integrate findings with existing data on primate skull form.
Main Methods:
- Allometric analyses of metric parameters related to masticatory function.
- Comparison of 47 strepsirhine and 45 anthropoid species, including basal anthropoids.
- Integration of morphological and experimental data on primate skull form.
Main Results:
- Crown anthropoids possess a vertically longer ascending ramus and higher glenoid/condyle compared to strepsirhines.
- Despite differences in ramus and joint height, both groups show similar ratios of condylar to glenoid height, suggesting comparable force distribution.
- Anthropoids exhibit more vertically oriented masseters and greater isognathy/isodonty than strepsirhines.
Conclusions:
- Differences in jaw-joint height are linked to facial height variations driven by encephalization, basicranial flexion, and facial kyphosis in anthropoids.
- The anthropoid masticatory pattern, characterized by vertical masseters and increased isognathy/isodonty, evolved stepwise during early anthropoid radiation.
- This pattern likely facilitated a more transverse and powerful masticatory stroke in early anthropoids.