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Anthropoid cranial base architecture and scaling relationships
1Doctoral Program in Hominid Paleobiology, Department of Anthropology, The George Washington University, 2110 G St., NW Washington, DC, 20052, USA. mccart@gwu.edu
Journal of Human Evolution
|January 5, 2001
Summary
Human cranial base length and flexion influence relative brain size calculations. While Homo sapiens have shorter cranial bases, their brain size relationship remains comparable to other anthropoids, challenging simple spatial packing hypotheses.
Area of Science:
- Paleoanthropology
- Comparative Anatomy
- Evolutionary Biology
Background:
- The "spatial packing" hypothesis suggests basicranial flexion maximizes braincase volume relative to basicranial length in haplorhines.
- Previous studies indicate Homo sapiens may have less basicranial flexion than expected, implying other factors influence hominin cranial base variation.
Purpose of the Study:
- To investigate how basicranial length and cranial base angulation measures impact the relationship between basicranial flexion and relative brain size in anthropoids, including Homo sapiens.
- To assess if Homo sapiens' Index of Relative Encephalization (IRE) is inflated due to shorter basicranial length (BL).
Main Methods:
- Midline cranial floor sections from 157 specimens across 18 anthropoid species were scaled relative to the cube root of endocranial volume.
- Analysis focused on the posterior cranial base and planum sphenoideum lengths and various cranial base angles.
Main Results:
- Homo sapiens exhibit significantly shorter posterior cranial bases and planum sphenoideum compared to other anthropoids, contributing to higher IREs.
- Including the cribriform plate in BL measurement alters the comparison of Homo sapiens' basicranial flexion versus IRE with other anthropoids.
- Despite shorter BL and elevated IRE, Homo sapiens do not significantly deviate from the general anthropoid trend for basicranial flexion versus relative brain size for two tested angles.
Conclusions:
- Shorter basicranial length in Homo sapiens contributes to elevated relative brain size indices.
- The equivocal findings on basicranial flexion in Homo sapiens highlight the impact of measurement choices for cranial base angulation.
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