The platypus’s mammary glands lack teats, with milk released through pores in the skin. The milk pools in grooves on the mother’s abdomen, allowing the young to lap it up.[16][71] After they hatch, the offspring are milk-fed for three to four months.
It’s thought that this was the ancestral state, and that specialized ducts (eventually nipples) evolved later on eutherian mammals.
Edit: I recognized my error moments later when I realized that marsupials have nipples too. So this evolved after marsupials and eutherians split from monotremes.
Wow, TIL.
https://wikipedia.org/wiki/Platypus
It’s thought that this was the ancestral state, and that specialized ducts (eventually nipples) evolved later on eutherian mammals.
Edit: I recognized my error moments later when I realized that marsupials have nipples too. So this evolved after marsupials and eutherians split from monotremes.