Way I heard it, Cubone lives and wears his mother's skull as a sign of mourning. So we have never seen the faces of Cubone or Marowak.

I love how Lavender Town is so creepy, Nintendo has never made anything like it since, it adds to the legend. Personally, I think they knew exaclty what they were doing back at Game Freak, they must have known players would get attached to their Pokemon, but lose a few to errors, entire games to batteries dying... so, here is a virtual shrine to all the lost pokemon, and there has been a pokemon cemetary in every games since.