Energetic benefits and adaptations in mammalian limbs: scale effects and selective pressures

Differences in limb size and shape are fundamental to mammalian morphological diversity; however, their relevance to locomotor costs has long been subject to debate. In particular, it remains unknown if scale effects in whole limb morphology could partially underlie decreasing mass-specific locomotor costs with increasing limb length. Whole fore- and hindlimb inertial properties reflecting limb size and shape – moment of inertia (MOI), mass, mass distribution, and natural frequency – were regressed against limb length for 44 species of quadrupedal mammals. Limb mass, MOI, and center of mass position are negatively allometric, having strong potential for lowering mass-specific locomotor costs in large terrestrial mammals. Negative allometry of limb MOI results in a 40% reduction in MOI relative to isometry for our largest sampled taxa. However, fitting regression residuals to adaptive diversification models reveals that co-diversification of limb mass, limb length, and body mass likely r...