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Variations in humeral and femoral strains across body sizes and limb posture in American alligators

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posted on 2024-12-08, 10:12 authored by Masaya IijimaMasaya Iijima, David Munteanu, Richard Blob

Bone loading is a crucial factor that constrains locomotor capacities of terrestrial tetrapods. To date, limb bone strains and stresses have been studied across various animals, with a primary emphasis on constant bone loading in mammals of different sizes and variations in loading regimes across different clades and limb postures. However, the relationships between body size, limb posture, and limb bone loading remains unclear in animals with non-parasagittally moving limbs, limiting our understanding of the evolution of limb functions in tetrapods. To address this, we investigated in vivo strains of the humerus and femur in juvenile to subadult American alligators as they walked with various limb postures. We found that principal strains on the ventromedial cortex of the femoral midshaft increased with larger sizes among the three individuals displaying similar limb postures. This indicates that larger individuals experience greater limb bone strains when maintaining similar limb postures to smaller ones. Axial and shear strains in the humerus were generally reduced with a more upright limb posture, while trends in the femur varied among individuals. Given that larger alligators have been shown to adopt a more upright limb posture, the transition from sprawling to upright limb posture, particularly in the forelimb, might lead to or result from the evolution of larger body sizes in archosaurs. Moreover, both the humerus and femur experienced increased shearing compared to axial loads with a less upright limb posture, suggesting proportional changes in bone loading regimes throughout the evolution of limb posture.

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Japan Society for the Promotion of Science

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