When animals lose something,
be it a tail, finger, limbs, eyes or teeth, usually a vestige is left behind.
When turtles lost their ancestral teeth,
they should have left empty alveoli along their jaw rims. And the place to look for empty alveoli in turtles is in the most primitive turtle in the large reptile tree, the late-surviving Niolamia (Fig. 1), one of the great horned meiolaniid turtles.
along the maxilla (Fig. 1) seem to show where tiny teeth once erupted in Niolamia.
Earlier we looked at similar alveoli in the jaw tips of a gray whale where desmostylian tusks once emerged.