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Neurocranial narrowness across nonhuman anthropoid primates

Mormile, Isabel1; Percival, Christopher1; Rossie, James1

Published Feb 28, 2026 on Dryad. https://doi.org/10.5061/dryad.r4xgxd2r0

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Abstract

Body size allometry has been proposed to explain neurocranial shape variation across platyrrhine monkeys, including the extreme neurocranial narrowness (NCN) of small-bodied taxa. However, catarrhine primates do not align with the proposed platyrrhine allometry, suggesting that body size alone may not explain anthropoid NCN variation. We measured NCN in platyrrhine and catarrhine anthropoids, and identified inter-clade differences in degree and allometric scaling of NCN using GLS pANCOVA, a method combining generalized least squares analysis and phylogenetic analysis of covariance. We further performed character history analysis using extant anthropoid data and fossil evidence to estimate neurocranial shape in anthropoid ancestors. We found no unified allometry of NCN across platyrrhines or across anthropoids as a whole, and there was no significant correlation between body mass and NCN across platyrrhines or catarrhines. At the subfamily level, callitrichine and possibly cebine platyrrhines differ from other anthropoids in degree and allometric scaling of NCN. Character history analysis suggests that higher NCN is the ancestral platyrrhine condition, and broader neurocranial shape evolved independently in catarrhines and larger-bodied platyrrhines. Our results support the hypothesis that body size does not explain anthropoid NCN variation, and provide a foundation for future research into potential correlates of anthropoid NCN.