Cranial Structure and Evolution in 'Alouatta': Temporal Fossa and Interorbital Morphology

The genus 'Alouatta' is characterised by a peculiar cranial morphology, in which the splancnocranium appears as sagittally rotated with respect to the neurocranial axis. This process is called 'airorhynchy' and distinguishes the genus 'Alouatta' from all the other atelids. Previous analyses suggested that airorhynchy in 'Alouatta' is associated with the relationship between basi-cranial flexion and neurocranial development. Within this process, changes at the temporal fossa may represent a major structural rearrangement. In this paper, the area of the pterion in 'Alouatta' is investigated through Procrustes superimposition and thin-plate spline. The anatomy of the interorbital area has also been examined and described, since it represents a further source of variation among the atelids. The structural role of the temporal fossa is evidenced, while the interorbital morphology supports some phylogenetic hypotheses. Results are discussed considering the debate on the phylogenetic position of 'Paralouatta varonai' from the Quaternary of Cuba.