How do the ankle bones of artiodactyls differ from those of other mammals?

The ankle structure of artiodactyls is distinct from that of other mammals primarily due to the unique morphology of the astragalus.

In most mammals, the astragalus features a single rounded articulation situated above a constricted neck. In contrast, the artiodactyl astragalus lacks this constricted neck and instead possesses both upper and lower rounded articulations. Additionally, the artiodactyl astragalus includes an articulation on its rear surface for the calcaneum (heel bone). These three articulations are arranged in nearly parallel planes, which allows the bone to rotate vertically.1

This increased rotation of the astragalus is a key adaptation for fast running, as it enhances propulsive thrust at the ankle and facilitates a quicker recovery at the end of a stride. Furthermore, while some artiodactyls like pigs, hippopotamuses, and camels retain separate navicular and cuboid bones in the ankle, many other lineages have evolved a fused naviculo-cuboid bone to better withstand the strain of impact on uneven ground.2