Are there any "skeletons" I can use as a base for humanoid animation and possibly quadruped animiations?
I can recommend Poser. The older versions are sometimes available for free on the web.
The completely free alternative would be Makehuman, however i don't know how far they are in terms of animation
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You could use Pivot to position the animation skeleton-wise then draw graphics over it <img src="{SMILIES_PATH}/icon_e_smile.gif" alt=":)" title="Smile"> http://pivotanimator.net/Download
Otherwise Spriter has Construct 2 support: http://www.brashmonkey.com/