Jābir reports the Messenger of Allah forbade the use of camel bones or droppings for wiping (after excretion).
-Sunnah (Tradition) of Sahīh Muslim (9th C CE), Book 2:263
That makes perfect sense, there being so many smoother objects found on the Darb. Ostrich shells, petrified wood, Siyal leaves, Colocynth gourds. As a Tradition never put it, When holding a hammer in the desert, what doesn’t look like a nail might still scratch your ass.