Abstract
The origin of aerial birds from terrestrial dinosaurs is a well accepted theory. However, understanding how this transition occurred requires knowledge of which intermediate forms where able to fly and how proficient that flight was. Such knowledge can be gleaned, to some extent, from gross morphological studies but, at times factors such as unpreserved feathers can lead to inconclusive results. In recent years compact bone microstructure was found to differ in bones that experienced consistently distinctive loads. Here we experimentally tested how differently fore- and hind-limbs are loaded during flight and running and if such loading leads to predictably differing bone microstructure. Groups of Helmeted Guinea Fowl (Numida meleagris) were subjected to flying or running exercise throughout growth while a third group had their movements restricted. Bone strain was measured in the fore- and hindlimbs of all three groups. Bone microstructure parameters such as vascular orientation, bone density, bone deposition rate, secondary remodeling rate and cross sectional geometry were compared between groups. Results indicate that bone microstructure does differ predictably between animals that are running and those that are flying. These results are compared to other bone microstructure studies that observe flying and running species. Commentary will be given on how best to apply these results to better understand the origin of flight in birds.