You're going to want to call the PA Game Commission, because laws in this state are weird. Shed hunting (collecting dropped antlers) is legal, as long as you aren't trespassing, but you cannot collect antlers attached to a head/skull (meaning you can't take them from a dead animal). Obviously bones aren't quite the same as antlers, but you'd be best off calling them to make sure you don't run afoul of any weird rules like that.