>>17856228 (OP)>Did they?Maybe.
There's a condition that makes women look like that called "Steatopygia"; it causes a woman's ass to stick out so much it looks like a shelf, and is associated with gigantomastia (hyper breasts), and a more flush/thicker labia and an overall increase in penis size (longer and thicker) in men.
This gene is still commonly present in southern african populations, and some south east asian populations, but isn't otherwise as present as it "may have been" during Mesolithic caveman times when those figures were being carved. They may also be depicting "fat farming": where a girl is fed large quantities of starch and milk in order to become morbidly obese for marriage - a tradition still practiced in those aformentioned areas as well.