"??????? I'm going to say they are not primitive. The slots and glue joints look too precise (modern saw). I was thinking strap on horns but the decorations would not face forward and the holes?????????.
I thought maybe the slot was for a ruler…"
"Hollow like a bored hole connecting the two or hollowed out cone shaped clear down to the slot? More pix might help. Loving the puzzle. Any smell of smoke? Where the holes drilled or burned in? Do they stand up straight?"