Meeting Abstract

8.3  Jan. 4  Musculoskeletal scaling of the hindlimb of kangaroos and wallabies (Superfamily Macropodoidea) MCGOWAN, C. P.*; SKINNER, J.; BIEWENER, A.A.; University of Colorado at Boulder; University of South Australia; Harvard University mcgowac@colorado.edu

This study seeks to extend prior analysis of the locomotor mechanics and physiology of marsupial hopping by examining how the hindlimb musculoskeletal system scales with body mass in species of Macropodoidea, the superfamily containing wallabies and kangaroos. We do this to provide a broader context for interpreting empirical results obtained from experimental studies carried out on a more restrictive sample of members of this group. A morphometric analysis was conducted on cadavers of 15 species and skeletal specimens of 21 species spanning a size range from 0.8 to 27 kg, which included representatives of 12 of 16 extant genera of this group. The results of this analysis indicate that macropodoids are able to match increasing force demands associated with increasing body size primarily through a combination of a disproportionate increase (positive allometry) in muscle area and muscle moment arms, with relatively little change in locomotor limb posture. In contrast, isometric scaling of the primary long bones of the hindlimb suggest that larger animals experience relatively greater bone stresses. As previously observed, muscle to tendon area ratios of the ankle extensors scaled with strong positive allometry indicating that peak tendon stresses also increase with increasing body size, but to a lesser degree than previously reported. Consistent with previous morphological and experimental studies, large macropodoids are therefore better suited for elastic strain energy recovery, but operate at lower safety factors which likely poses a limit to body size. Our data suggests extinct giant kangaroos (~250 kg) were likely quite limited in locomotor capacity.