Although endocasts from fossil primates have been extensively examined in several previous studies, relatively little is currently known about the genetic and environmental factors that affect brain development in extant non-human primates. We examined the effects of age and sex on brain size and external morphology in a large sample of rhesus macaque endocasts from the Cayo Santiago skeletal collection. Using a repeated measures design, we demonstrated that brain sulcus lengths can be reliably assessed with current computer input technology and careful trait definition. Age and sex variation in sulcus lengths and endocranial capacity were also analyzed using ANCOVA and maximum likelihood estimation methods. Our cross-sectional data indicated that total cranial capacity increases postnatally in the macaque, while the cortical sulci appear to have reached their adult length at or soon after birth. Cranial capacity reaches its adult volume at 3·57 years in females, but not until 6·08 years in males. We also found considerable sexual dimorphism in brain sulcus lengths with males larger than females, particularly for the more posteriorly located sulci. The dimorphism is, however, a function of overall brain size. After controlling for cranial capacity, there is no sexual dimorphism for sulcal lengths.
- brain sulci
- rhesus macaque
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics