The mad scientist community is...mad, to put it kiddie-appropriately. Their logic has the tendency to make 0% sense 100% of the time (provided, of course, that they ever bring it up.)
So you can imagine a field scientist's confusion when the community tasked him to imagine a hybrid between a wild bison (they never specified which species) and a wild aurochs through their bones alone because hybrids between wild bison and domesticated aurochs are so done before. The problem with that is that the scientist has observed only live bison and never once studied their skeletons, and he had never seen a live wild aurochs. (In fairness, NO ONE has seen a live wild aurochs for roughly three centuries.) In short, he couldn't tell the two species apart just by looking at their bones.
In order to save his skin, he would need help from a higher power (that's us.) So, comprehensively speaking, just by looking at the bones alone, how would the field scientist differentiate a wild bison from a wild aurochs?