I found this on the Yellowstone River after high water, it had washed onto an island on the river and gotten caught in an old tree that was also beached on the island. It is 22" from tip to tip and heavier than I would have expected as if it has begun mineralization. The base of the horn cones are 3 1/8" at their largest dimension. Could this be a Bison Antiquus? Any insight would be greatly appreciated.