Do forelimb shape and peak forces co-vary in strepsirrhines?

Area of Science:

• Primate anatomy and biomechanics
• Evolutionary biology
• Paleontology

Background:

• Strepsirrhine primates exhibit diverse arboreal locomotion and forelimb morphologies.
• Understanding the relationship between bone shape and mechanical forces is crucial for interpreting fossil evidence and evolutionary adaptations.

Purpose of the Study:

• To investigate the covariation between forelimb long bone shape and ground reaction forces during horizontal walking in strepsirrhines.
• To determine how locomotor mechanics influence skeletal morphology in arboreal primates.

Main Methods:

• Quantified forelimb long bone shape using geometric morphometrics.
• Measured peak vertical, mediolateral, and horizontal ground reaction forces during arboreal locomotion in eight strepsirrhine species.
• Analyzed covariation between bone shape and forces within a phylogenetic framework.

Main Results:

• Significant differences in ground reaction forces and bone shape were observed among strepsirrhine groups (e.g., lorises, sifakas, lemurs).
• Propulsive and medial peak forces most strongly influenced humerus shape.
• Covariation between long bone shape (humerus and ulna) and ground reaction forces was detected, independent of body mass.

Conclusions:

• Locomotor forces, particularly propulsive and mediolateral components, significantly shape forelimb bone morphology in strepsirrhines.
• Functional interpretations of primate skeletal morphology should consider a broader range of limb-loading forces beyond peak vertical forces.
• These findings necessitate a re-evaluation of osseous morphology and functional interpretations in primate evolution.