The foot pads of many mammals provide cushioning using hydrostatic structures, essentially working as fluid-filled cushions.
"Human heel pads and other mammalian foot pads make use of hydroskeletal support; our pads, which provide impact damping, some energy storage, and protection for bones, work as fluid-filled cushions--see, for instance, Ker (1999). They're complexly viscoelastic--if you want a stable reading of your height, you should stand for almost two minutes to allow your pads to creep into stability (Foreman and Linge 1989)." (Vogel 2003:417)
Learn more about this functional adaptation.