Answer: monotremes

AnswerCrossword Clue
monotremesA primitive mammal that lays large yolky eggs and has a common opening for the urogenital and digestive systems. Monotremes are now restricted to Australia and New Guinea, and comprise the platypus and the echidnas
monotremesMONOTREME, a primitive Australian egg-laying mammal, eg a duck-billed platypus