Patterns of cranial shape variation in the Papionini (Primates: Cercopithecinae)

Area of Science:

• Primate evolution
• Comparative anatomy
• Morphometrics

Background:

• Traditional classifications of Old World monkeys (tribe Papionini) considered mangabey genera (Cercocebus and Lophocebus) as sister taxa.
• Molecular studies reveal a diphyletic nature, with Cercocebus and Mandrillus forming a distinct clade, challenging traditional views.

Purpose of the Study:

• To evaluate the hypothesis that allometric scaling contributes to craniofacial similarities among papionin taxa of similar size.
• To describe patterns of allometric and size-independent cranial shape variation in relation to phylogeny and development.

Main Methods:

• Employed geometric morphometrics, bivariate, and multivariate analyses.
• Examined cranial shape variation, considering allometric scaling and size-uncorrelated differences across papionin genera.

Main Results:

• Confirmed significant allometric scaling (positive facial, negative neurocranial) across adult papionins.
• Identified homogeneity in scaling but also significant differences, particularly between Cercocebus and Lophocebus, which share a slope but have distinct allometric lines.
• Size-uncorrelated shape variation did not strongly support molecular phylogenies but highlighted differences between mangabey genera when size effects were controlled.

Conclusions:

• General allometric trends explain substantial cranial shape variation in Papionini, influencing traditional morphological phylogenies.
• Lophocebus exhibits a distinct morphometric pattern, separate from other papionins, including Cercocebus.
• Findings clarify cranial variation patterns in extant Papionini and inform studies of fossil taxa.