# Why Are Birds' Knees Backwards?



## Vishatrove (Feb 10, 2014)

I've always wondered why birds have knees that are backwards. Or is it humans that have the backwards knees? :laugh: But, it looks as if birds' knees go in the opposite direction as ours. Or am I wrong here? To me, they look like they bend backwards. But, the definitely bend backwards at the halfway mark. Or is this their ankle? Is the top bone of their leg the femur? I've watched my neighbor's chickens walk and their knees (or maybe ankles) bend backwards. Maybe it's just our knees that are weird! I guess it's all biological. You would think that our knees would be higher up to distribute our body weight, right? This is why birds have knees that are higher up, right? Maybe it's that way so they can lay their eggs easier. Maybe I'm just confused and am looking at their ankles. Their wings are bent in the opposite direction from our arms, too. I guess I"m just curious and wanted to know why their knees bend backwards. Or why theirs bend the right way and our bend backwards. :laugh: If I'm wrong, sorry for wasting your time. I could very easily be wrong. It looks like their knees. But, I could be looking at the ankle. I'm not a vet. Chickens just look like they walk weird! :laugh:


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## Ceiling Kitty (Mar 7, 2010)

Vishatrove said:


> I've always wondered why birds have knees that are backwards. Or is it humans that have the backwards knees? :laugh: But, it looks as if birds' knees go in the opposite direction as ours. Or am I wrong here? To me, they look like they bend backwards. But, the definitely bend backwards at the halfway mark. Or is this their ankle? Is the top bone of their leg the femur? I've watched my neighbor's chickens walk and their knees (or maybe ankles) bend backwards. Maybe it's just our knees that are weird! I guess it's all biological. You would think that our knees would be higher up to distribute our body weight, right? This is why birds have knees that are higher up, right? Maybe it's that way so they can lay their eggs easier. Maybe I'm just confused and am looking at their ankles. Their wings are bent in the opposite direction from our arms, too. I guess I"m just curious and wanted to know why their knees bend backwards. Or why theirs bend the right way and our bend backwards. :laugh: If I'm wrong, sorry for wasting your time. I could very easily be wrong. It looks like their knees. But, I could be looking at the ankle. I'm not a vet. Chickens just look like they walk weird! :laugh:


It's their ankle.

They do have knees like us, but they are higher up and obscured by feathers. You can easily see them on a plucked whole chicken from the supermarket.


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## Vishatrove (Feb 10, 2014)

I was thinking it could be their ankle! I thought maybe the higher joint was the knee. I can't say I've ever plucked a bird!


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## Ceiling Kitty (Mar 7, 2010)

Vishatrove said:


> I was thinking it could be their ankle! I thought maybe the higher joint was the knee. I can't say I've ever plucked a bird!


Well pop 'whole chicken' into Google images and you can see for yourself.


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## Vishatrove (Feb 10, 2014)

Okay, I see what you mean.


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## Phoenix24 (Apr 6, 2013)

Birds knees are thought to have evolved to be more within the body as a space-saving, aerodynamic function - the less leg poking out the less drag when they fly. Obviously some birds have since lost the ability to fly, but leg structure remains largely similar.

eg

http://www.animalcorner.co.uk/wildlife/graphics/ostrich.jpg

You can clearly see the knee joint of the ostrich by the body.

If you look at archaeopteryx - thought to be the earliest ancestors of birds - the knee joint is still free.

https://www.google.co.uk/search?q=a...2y7Ab-nIG4DA&ved=0CAkQ_AUoAQ&biw=1454&bih=704

A bird's leg structure is much reduced overall - again for flight - with several bones fused (plus their hollow centres) to reduce weight. The tibiotarsus, for example, comprises of the tibia (our shin bone) with the tarsals (foot bones) - this is above the ankle joint.

http://people.eku.edu/ritchisong/birdskeleton.jpg

There is a similar reduction in the birds wing, whereby the wrist bones are reduced (the carpometacarpus), and the phalanges (finger bones) are reduced to just three.

Hope that helps - i'm in a bit of a hurry or else would have given you a much more detailed answer


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## Vishatrove (Feb 10, 2014)

That is very interesting. I wonder why flightless birds have such similar legs to flighted birds. The knees on an ostrich are what I would assume to be the hipbone. I cant really tell where the knee is on an archaeopteryx. I guess fusing some bones would make flight much easier. The skeletal picture helped a lot. I appreciate your answer.


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## Phoenix24 (Apr 6, 2013)

They also have a completely different pelvic structure.

Skeletal Adaptations of Birds for Flight Has some information on a birds skeletal adaptations for flight.

As for flightless birds - secondary loss of flight doesn't necessarily mean they need to 'lose' structures associated with flight. Ostriches and other flightless birds still have feathers - though in some groups the feather structure has altered (eg become loose and fluffy as they no longer need to be stiff for flight). They still have wings, too, though they might be much reduced in size (eg the kiwi). The ostrich has other adaptations for running (reduction in toes) but apparently there is no benefit in altering knee position, which must have taken a few million years in itself to evolve.

Archaeopteryx (and other pre-birds/early birds) pretty much looks like a dinosaur with feathers. Think of the likes of veloceraptor, T-rex and similarly shaped dinos - they have knees like archaeopteryx.


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