The elephant is also the only mammal with four knees.
It is impossible to jump without knees.
Based on this information, I can only assume that in order for a mammal to jump it must possess at least one, but less than four knees. In other words,
More research is needed on one and three legged mammals, but I think the basic concept of my theory is pretty solid. Feel free, biologists, evo-devos and mathematicians to expound on my work, but please have the courtesy to give credit where credit is due when using my equation(s).