Hyoid Bone Size and Its Implications for Social Organization and Sexual Selection in Alouatta pigra and the Elusive Alouatta macconnelli

The purpose of this research paper is focusing on the hyoid bone in Alouatta pigra and Alouatta macconnelli and determine its role in affecting the social organization and sexual selection of the individuals in these species. This includes the discussion on the dimensions of the hyoid between the males and females as well as an analysis of observed social behaviour patterns and the sexual selection process. It was found that female Alouatta pigra had a larger hyoid than males of the species and that Alouatta macconnelli males had a hyoid nearly twice the size of females. The hyoids were measured from the Mammal Biodiversity collection at the Royal Ontario Museum. The bones dimensions were taken using plastic calipers and their circumference measured using a soft tape measure. Based on the sexual selection and social organisation of Alouatta pigra which is multi-male/multi-female with the occasional unimale with multiple females, the null hypothesis must be accepted as the larger hyoid is not found in males but in females and the size of the hyoid does not affect the social organization in this species. In Alouatta macconnelli, there is little information on this species but the null hypothesis is rejected as males have much larger hyoids than females and the social organization is that of a uni-male with multiple females.