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Basicranial flexion, relative brain size, and facial kyphosis in nonhuman primates
1Department of Biological Anthropology and Anatomy, Duke University Medical Center, Durham, North Carolina 27710.
American Journal of Physical Anthropology
|July 1, 1993
Summary
The study found that in haplorhine primates, a larger brain size relative to basicranial length correlates with a less flexed cranial base. This suggests brain size, not just posture, influences basicranial flexion in primates.
Area of Science:
- Primate Anatomy
- Evolutionary Biology
- Comparative Morphology
Background:
- Interspecific variation in basicranial flexion is explained by multiple hypotheses, including brain size and postural behavior.
- Previous research suggests a link between basicranial flexion, brain size, and orbital orientation.
Purpose of the Study:
- To test hypotheses relating basicranial flexion to brain size, postural behavior, and facial orientation in primates.
- To investigate the anatomical and evolutionary factors driving differences in cranial base flexion across primate species.
Main Methods:
- Measured cranial base angle, palate orientation, and orbital axis orientation from lateral radiographs of 68 primate species.
- Combined morphometric data with linear and volumetric measurements of the neocortex and telencephalon.
- Utilized bivariate correlation and partial correlation analyses across different taxonomic levels.
Main Results:
- Within haplorhines, a larger cranial base angle (more flexion) correlates with increased neurocranial volume relative to basicranial length.
- Cranial base angle is positively correlated with facial kyphosis and orbital axis orientation in haplorhines.
- No significant correlations were found between cranial base angle and the examined variables in strepsirhines.
Conclusions:
- The findings support the hypothesis that increased relative brain size contributes to basicranial flexion in haplorhines.
- Orbital approximation in ancestral haplorhines likely integrated the medial orbital walls and pre-sella basicranium, influencing cranial base morphology.
- The study corroborates Gould's hypothesis regarding the role of large brain size and a short basicranium in the highly flexed cranial base of Homo sapiens.