1) Deer antlers are made of bone, but rhino horns consist entirely of keratin (the same stuff as your nails).
2) Most people have 24 ribs in total, but one in 200 people have an extra one. This is more common in females than males.
3) Most primates including chimpanzees have a bone inside their penis called the baculum (which is Latin for stick or staff). While the remnants of the coccyx tailbone have remained during our evolutions, humans don’t even have a trace of the penis bone left.