Longitudinal study of cranial base shape changes in Macaca nemestrina

Area of Science:

• Primate morphology
• Developmental biology
• Biometrics

Background:

• The primate cranial base (CB) is a complex 2D structure challenging to quantify using traditional methods.
• Conventional metrical approaches (angles, distances) are insufficient for describing its intricate shape.

Purpose of the Study:

• To apply elliptical Fourier functions (EFF) for quantitative analysis of primate cranial base shape.
• To document shape changes in the Macaca nemestrina cranial base from 1 to 8 years.
• To identify age-related and sexually dimorphic shape variations.

Main Methods:

• Utilized a longitudinal sample of 181 Macaca nemestrina lateral headfilms (1-8 years).
• Applied elliptical Fourier functions (EFF) with 20 harmonics to digitized CB outlines.
• Generated expected distances from the centroid to the CB boundary for shape analysis.

Main Results:

• Statistically significant shape differences were observed based on age and sexual dimorphism.
• Age-related changes included anteroposterior lengthening and superoinferior narrowing of the CB.
• Specific changes noted: lengthening of the dorsal clivus and anterior migration of the hypophyseal fossa.

Conclusions:

• Elliptical Fourier functions (EFF) offer a powerful method for quantifying complex 2D morphologies like the primate cranial base.
• This approach enables detailed visual and numerical documentation of developmental shape changes.
• The study highlights significant ontogenetic and dimorphic variations in primate CB development.