I believe this is an example of parental care. Mammals nurse their young ones by giving them milk produced from the mammary glands. In all mammals except monotremes, the milk is transferred from the mammary gland to the baby's mouth through the a nipple. In monotremes the Echidna and the platypus, the milk is secreted onto the surface of the skin like sweat and licked off the body hairs by the young.
