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"Reverse knees" is a funny term for ankles. Penguins are another unique animal, they have very low ankles (and high knees, hence the waddling) and also seem to

• iggldiggl 5y ago
  And kangaroos? Okay, so their knees are possibly somewhat more inconspicuous, but looking at a kangaroo skeleton, what to my eyes looks like their ankles also actually is their ankles. Whereas with birds the confusion comes in because a) they're walking on their toes, so what to us looks like an ankle is in fact a toe joint, and then moving further up what we think looks like a "reverse knee" is in fact the actual ankle, and b) their true knees are usually hidden somewhere beneath their feathers
• usrusr 5y ago
  And even we humans switch to "heel up" for high intensity bipedalism. Are we are secret members of the reverse knees club?