A digital biomechanical contribution to the debate on whether giant kangaroos could hop

Abstract

<p>Recently the hopping capability of Sthenurinae, extinct short-faced kangaroos, has become heavily debated. While much of the research has centred on skeletal morphology, there has been little work on the biomechanics of Sthenurinae. This thesis investigates whether one of the larger macropodoids, <em>Simosthenurus occidentalis</em>, would be capable of withstanding the forces that would be required for an animal of such size to hop.</p><p> This thesis is innovative to the topic of sthenurine locomotion and to a broader extent macropodoid locomotion, as it is the first to specifically incorporate finite element analysis to the hind limbs of <em>S. occidentalis</em> and many other macropodoids. This research is broken into three parts. First, a comparison of peak ground reaction force in the femur of <em>S. occidentalis</em> and thirteen other macropodoids, comparing the stresses generated during hopping at equal moment arm and equal internal loads relative to body mass. Secondly, I investigated muscle moment arms by reconstructing the muscular of <em>Macropus giganteus, Dengrolagus lumholtzi</em> and a possible muscular system for <em>S. occidentalis</em> based off of the musculature of the two extant species (<em>M. giganteus</em> and <em>D. lumholtzi</em>). These models were then compared to determine at what joint angle muscle moment arms would be the largest, and at what joint angle the greatest percentage of muscles would produce their largest moment arm in order to determine a probable limp posture for optimal body support in <em>S. occidentalis</em>. Finally, I conducted a second FEA on muscle forces which investigated if the forces required by the muscles during hopping would generate reasonable stress for <em>S. occidentalis</em>.</p><p> By comparing ground reaction force, results indicated that despite the relatively gigantic size (compared to many extant species of Macropodoidea today) <em>S. occidentalis</em> would generate stress equivalent to a species roughly 25 times smaller in body mass, In addition analysis of muscle moment arms indicated that <em>S. occidentalis</em> would produce its largest moment arms at joint angles closer in similarity to <em>D. lumholtzi</em> than to <em>M. giganteus</em> and would do so at limb postures relatively more up right than the two extant species. Finally in comparing muscle forces, results again indicated lower than predicted stress for <em>S. occidentalis</em>. Based on my results, I suggest that <em>S. occidentalis</em> might be capable of hopping but might also use striding for lower speed travel.</p>