Cranial shape variation in adult howler monkeys (Alouatta seniculus)

In this study we quantitatively analyzed the cranial shape variation in Alouatta seniculus, to evaluate possible influences and constraints in face and braincase associated with airorhynchy. We also considered the structural role of the pteric area within the cranial functional matrix. We applied landmark‐based analysis and multivariate statistics to 31 adult crania, computing shape analyses based on 3D coordinates registration as well as the analysis of the Euclidean distance matrix to investigate patterns of intraspecific morphological variability. Our results suggest that allometry is the main source of variation involved in shaping cranial morphology in howlers, influencing the degree of facial proportions and braincase flattening, and generating the main sexual differences. Larger individuals are characterized by a higher degree of airorhynchy, neurocranial flattening, and expansion of the zygomatic arch. Allometric variations influence the skull as a whole, without distinct patterns for face and braincase, which behave as an integrated morphological unit. A preliminary survey on the pteric pattern suggests that the morphology of this area may be the result of variations in the vertical growth rates between face and braincase. Future studies should be dedicated to the ontogenetic series and focus on airorhynchy in terms of differential growth among distinct cranial districts.
Source: American Journal of Primatology - Category: Psychiatry & Psychology Authors: Tags: RESEARCH ARTICLE Source Type: research