As someone who is writing one and went off a deep end in doing so, basically --
Southern Minotaurs are the ones Brint and Brienne belong to. Their men are on average large, muscular behemoths that have more of a resemblence to the minotaur of myth wih their cow heads, furried bodies and hooves. Their women are shorter by quite a bit, possesing humanoid faces instead of snouts. The men tend to be more dommy while women more subby.
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Northern minotaurs basically just switch roles. Their women are the large, strong ones (albeit more fluffy) while their men are mostly human faced twinks. Their women tend to be more dominant, their men more subservient.
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Basically this.