Modeling the functional morphologic relationship between orbital hypertrophy and choanal dimensions: A 3D geometric morphometric study of the owl monkey

The owl monkey (genus Aotus) is well known for its orbital hypertrophy, possessing the largest orbit size among anthropoid primates. This study used Aotus as an anatomical model to test the relationship between orbit size and choanal morphology. Three‐dimensional landmark coordinate data were collected from a dry cranial sample representing Aotus (n=116) and a taxonomically diverse out group of other New World (platyrrhine) genera (n=371). Coordinate data was subjected to Procrustes scaling so that linear, angular, and volumetric measures could be directly compared with Student's T‐tests (Bonferroni‐adjusted). Males and females were pooled as no dimorphism in orbital or nasopharyngeal morphology was detected. Restults show that Aotus was found to possess significantly (p<0.05) greater orbital dimensions (width and area of the orbital rim and orbital depth). However, its choanal height, width, area, and angulation were found to be nested among other platyrrhines. Orbital volume showed a relatively weak (r2=0.42) but significant (p<0.0001) correlation with choanal width, which was more strongly correlated with upper facial height (r2=0.56, p<0.0001). The results indicate that orbital hypertrophy in Aotus does not share a strong functional morphologic relationship with choanal morphology. This portion of the upper respiratory tract thus appears functionally constrained among the taxa sampled. Grant Funding Source : Center for Anatomy and Functional Morphology