What the ??????

I was beachcombing for Seaglass at Auds request, and playing with a macro lens.
Turning over a rock I found this tiny crab.
No bigger than my little finger nail.
Took the photo and almost discarded it .
Over the next hour or so I took several much better macro images
Back at Base, I was reviewing these images for a blip and had to look twice at this.
Are those fossilised teeth?
Finding that rock will be like looking for a needle on a haystack, only harder.