Osteoderm distribution has low impact on the centre of mass of stegosaurs

Abstract. It has been hypothesized that the pronounced differences of stegosaur humeral shapes, with large forms having more slender and small forms having more robust humeri, may be explained by a difference in relative centre of mass (COM) placement caused by differing distributions of osteoderms. To test this hypothesis, digital 3-D models of the bones and osteoderms of the Tanzanian stegosaur Kentrosaurus aethiopicus and of the North American stegosaur Stegosaurus armatus were used to create a 3-D computer-aided design life reconstruction. On these models osteoderm placement was varied drastically, recreating both existing and hypothetical forms. These models show that COM position varies somewhat with realistic osteoderm distributions, but insufficiently to explain major differences in humeral shape. The uniform weight distribution between forelimbs and hindlimbs found between the two taxa also casts doubt on the hypothesis that differences in relative COM position caused by other factors than osteoderm distribution can explain differences in humeral robustness.