Thanks to my friend Jill, the mystery bone has been identified! It is a Guinea Fowl pelvis! A couple weeks ago we lost 3 birds to critters, and here I said "two other bones were by it that looked like chicken leg bones...." and I still didn't figure it out! Duh!
This is a site I found with a rough drawing:
Here is another site that shows how the pelvis sits on the legs.
Until later...Karen and Tripp