Step 15 (optional): For a cleaner look, erase as much as you can of the initial guide lines. Don't worry about erasing all of them. It's okay to leave some behind. Also re-draw any final sketch lines that you may have accidentally erased.
Final Step (optional): Add some shading to your drawing to give it more dimension and volume. Pick the direction of the light source when shading so that the shadows are consistent with it. Vary the pressure on your pencil to get different degrees of tonal value.
Add a cast shadow underneath. This helps ground the bison so it doesn't appear to be floating.
You can add more value throughout your bison drawing for extra detail. It's a good idea to use reference to be as accurate as possible.