Dear AS: I have seen squirrels grasp nuts, showing use of thumb. My daughter had
a pet coon that would gently take hold of dog's eyelid, and peek into eye. Dog knew
better than to move, fortunately. I have seen racoons grasping crayfish when eating
them. And dabbling food in water prior to eating.
But an anthropology site requires more than this to qualify for "opposable thumb":
"opposable thumb: an anatomical arrangement in which the fleshy tip of
the thumb can touch the fleshy tip of all the fingers."

I very much doubt that squirrels or coons can touch pad of thumb to tip of pinky.