Honestly I think stone could do it. I would use thick stone points made from some tough, uncooked stone. You want the point to maintain as much mass and cutting edge as possible. Of course a powerful bow and heavy arrows are definitely called for here. If you've got enough weight for your arrow it will drive that point deep into the vitals. But you'd also have to be close, and even with a double lung shot that beast is gonna take some time to die.