 A competing hypothesis is that , rather than being principally a feeding adaptation , the distinctive saddle shape and longer extremities might have been a secondary sexual characteristic of saddleback males . Male competition over mates is settled by dominance displays on the basis of vertical neck height rather than body size ( see below ) . This correlates with the observation that saddleback males are more aggressive than domed males . The shell distortion and elongation of the limbs and neck in saddlebacks is probably an evolutionary compromise between the need for a small body size in dry conditions and a high vertical reach for dominance displays . 
