Endocranial suture closure in rhesus macaques (Macaca mulatta)

Area of Science:

• Comparative Anatomy
• Primate Osteology
• Craniometry

Background:

• Cranial sutures are crucial for skull development and growth.
• Understanding suture closure patterns aids in age estimation and evolutionary studies.
• Previous research has established suture closure sequences in humans.

Purpose of the Study:

• To determine the sequence of cranial suture closure in rhesus monkeys (Macaca mulatta).
• To compare macaque suture closure patterns with those of humans.
• To assess the utility of suture closure for aging rhesus monkeys.

Main Methods:

• Analysis of endocasts from 330 rhesus monkeys of known age.
• Scoring of closure in nine bilateral and three unilateral cranial sutures.
• Statistical testing to establish relationships between age, suture closure, and side asymmetry.

Main Results:

• A strong correlation exists between age and suture closure stages, but precision diminishes in older macaques.
• The basilar suture closes earliest; masto-occipital and squamosal sutures close latest in both macaques and humans.
• Significant differences in closure timing were observed for the sphenofrontal and rostral squamosal sutures between species.
• Two sutures (rostral squamosal, masto-occipital) and potentially the lateral lambdoid suture show right-sided closure preference.

Conclusions:

• Macaque cranial suture closure sequences are established, revealing both similarities and differences with human patterns.
• Endocranial suture closure is a reliable indicator of age in younger macaques but less precise in older individuals.
• Directional asymmetries in suture closure may be linked to subtle asymmetries in brain and skull morphology (petalias).