Are there any birds whose legs fold the same way human legs do, in a knee, instead of an elbow which is what all the birds I know have?


The joint you are thinking of is not a knee, nor is it an elbow, instead it is an ankle which is bending the same way as us humans. You can see from the below diagram that the knee - the joint between the femur and tibia - is just further up the leg normally hidden by feathers.

Birds have a comparatively elongated metatarsus which gives the impression that the knee bends backwards more like an elbow, but it's just the ankle. (Image from here)

enter image description here

I also liked this diagram from a blogpost on a similar theme... enter image description here

To follow up there appears to be no animals whose ankles bend the "wrong" way.




Though these are far from conclusive resources. I'd guess the way knee is defined (it means something to humans but not to nature (a bit like the species being a concept which has weak biological bounds)) has something to do with that

  • $\begingroup$ Good point, thank you! It didn't occur to me. However, the joint I'm talking about is between Tibia and Metatarsus (ankle, right)? Are there any birds whose ankles bend backwards? $\endgroup$ – Violet Giraffe Oct 21 '14 at 16:12
  • $\begingroup$ according to the blogpost mentioned above no, no tetrapods do this $\endgroup$ – rg255 Oct 21 '14 at 16:14
  • $\begingroup$ @violetgirraffe edits made $\endgroup$ – rg255 Oct 21 '14 at 18:54
  • $\begingroup$ +1 Nice answer. You should add a reference to the first figure thought. $\endgroup$ – fileunderwater Oct 22 '14 at 10:51
  • $\begingroup$ Did you replace the first illustration? You shouldn't have, the other one was much larger and clearer; I can hardly read anything on this one. $\endgroup$ – Violet Giraffe Oct 22 '14 at 15:06

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