Figure 2.

Variation in Hyoid Morphology among Howler Monkey Species

(A) Phylogeny of the howler monkey (Alouatta) species studied, with Ateles fusciceps as an outgroup. Numbers at the nodes indicate the estimated dates for splitting events (Ma), where known (data from [21]).

(B) 3D models showing the variation in size and shape of average hyoids in males (left) and females (right), corresponding to the species in (A) (hyoids were not available for Alouatta pigra females).

(C) Computed tomography surface models, showing the hyoid (red) and thyroid cartilage (green). The left side of the mandible has been made transparent to make the hyoid bone fully visible.