Does ulnar curvature covary with locomotion and substrate use in cercopithecids?

Area of Science:

• Comparative anatomy
• Primate locomotion
• Functional morphology

Background:

• Ulnar curvature is a known indicator of mammalian locomotor behavior.
• Cercopithecids (Old World monkeys) display diverse quadrupedalism, making them ideal for studying ulnar curvature and locomotion.
• Mediolateral ulnar curvature remains understudied compared to anteroposterior curvature.

Purpose of the Study:

• To comprehensively assess ulnar curvature (anteroposterior and mediolateral) in extant cercopithecids.
• To test the hypothesis that ulnar curvature covaries with habitual substrate use (terrestrial vs. arboreal) and locomotor behaviors (suspension, climbing).
• To investigate inter- and intraspecific morphological variation in ulnar curvature.

Main Methods:

• Analysis of ulnar curvature in a diverse sample of 23 cercopithecid species (167 individuals).
• Examination of both anteroposterior (sagittal) and mediolateral (coronal) ulnar curvature.
• Correlation of ulnar morphology with known locomotor behaviors and substrate use.

Main Results:

• Confirms previous findings: terrestrial quadrupeds have anteriorly convex ulnae; arboreal taxa have anteriorly concave ulnae.
• Arboreal taxa show lateral ulnar convexity; terrestrial quadrupeds exhibit complex sigmoid mediolateral curvature.
• Suspensory taxa possess anteriorly concave ulnae, contrary to expectations; climbers show intermediate morphologies, making distinction difficult.

Conclusions:

• Ulnar curvature differentiates arboreal and terrestrial locomotion, but moderate covariation suggests distinct biomechanical drivers.
• Mediolateral curvature patterns in terrestrial cercopithecids may reflect adaptations to varied hand postures.
• Ulnar morphology alone is insufficient to reliably infer climbing behavior in cercopithecids.