Odd Bone Formation

[LMJEREZ]

HI: i was given this odd (and what I thought was just a wierd rock) about 30 years ago. I used to own a small thrift shop and I traded this rock for a coat with someone who said that he was from North Dakota and that his family owned alot of land and as a kid he and his brother would go out and just dig. One day, he said that they started digging and found this massive skelton of something. While both were digging, he was only able to get loose this piece of what I have pictured. So, I still have no other knowledge of what I have told you. As you can see from the pics, it looks to be a part of vertebrae or, as my best friend, she thinks it looks like a very large piece of a foot. She said that you can clearly see the toes and I was wondering if anyone could please identify this mystery stone/bone that I have.

[Auspex]

It is anatomically unlike any bone I have seen; I wonder whether it might be a geologic artifact?