In the animal kingdom there is a striking variety of pupil shapes, with great variety among relatively close relatives. Cats have vertical slits. Siberian tigers have round pupils. Cuttlefish have a W shape. Goats have what I would call a horizontal bar. Many foxes have vertical slits, many dogs have round ones.
I just started paying attention to it and I was looking at some good pictures of both Japanese and European squirrels. I sometimes feel that I see a round irregularity at the centre, but can never be sure.