I doubt I'm the first person to think of this, but I've had it floating around for a while now...
You ever notice how weird the Cubone line is, as a concept? Cubone is a nondescript animal thingy that wears its mother's skull on its head. Someone thought of that, folks.
But I think I've figured out where the idea might come from. You see, between the brain and skull lie the meninges - three membranes that function to protect the brain from mechanical injury, contain cerebrospinal fluid, and other fun stuff. The three membranes, going from inside out, are called the pia mater, arachnoid mater, and dura mater. They take the mater name from their actions of protecting and enveloping the brain - because mater is Latin for mother.
So really, all of us wear our mothers on our heads, protecting our brains.