Its a Thoratic Vertebrae from a Bison!
I realize what an odd title and post this is. To make any sense of it scroll down to the picture of Roman holding a large bone that he dug up at a lake.
After the last post I got the brilliant idea to do some research on the Internet...(in case you think I'm a little slow on the draw with that idea ...I guess I am. We have dial-up so looking up anything on the Internet is a time consuming process).
The bone is exactly the bone in the diagram below. I had no idea that Bison had bones that stuck up like that. I guess I should visit more with the Bison ranchers around us. I always assumed that hump was just fat, but you can see from the picture about how that ridge of bone shows on his back.
The mystery is solved.
I still have no idea how old the bone is. It is completely a brown color and has a strange porous consistency. It is likely at least a couple hundred years old since wild Bison haven't wandered the prairies in a long long time.
A pretty cool discovery for a 5 year old.