Possible ancient bison bones

[Creek - Don]

These bones were found just above Cretaceous gravel layer at a local DFW creek today.    One the leg bones measures almost 17 to 18 inches in length.   Leg bone width on this one is around 3 to 4 inches.   I also found vertebra bone of bison as well. They look juvenile.  These are probably either adult steppe bison bones or juvenile bones.  Earlier this month, at a another creek, I also found steppe bison dorsal vertebra with rib bones within similar layer.  Your opinion helps.   

 

[Creek - Don]

I identified that big old leg bone.  It's a horse femur.  Not sure whether recent or ice age. Horses were here during Pleistocene period, but became extinct.