Unidirectional air flow, whats the big d… oh.
Imagine your blood flow was not unidirectional. Not arteries and veins, just… vessels for both directions. You’d like – have to pump blood down into your extremities one heartbeat, and with the next one draw it back towards the heart. With the added malus that you only get partial replacement of blood, because you cant completely constrict your vessels.
You probably couldnt even leave your bed, let alone stand on two legs that way.
bone is less heavy than stone, also you can see bone has different surface structure.
Source: asked an archaeologist who thinks that although some people she knows do lik the bone, it’s not necessary.