Monotremes,like the duck-billed platypus,are egg-laying mammals covered in hair,have mammary and skin glands,have three ear ossicles,are diphyodont,and possess dentary-squamosal jaw articulation.Marsupials,such as kangaroos and koalas,are pouched mammals that have a vertical tympanic membrane in addition to possessing characteristics observed in monotremes.Eutherians,such as humans,are placental mammals that have a vertical tympanic membrane in addition to possessing characteristics observed in monotremes. What one shared derived trait sets marsupials and eutherians apart from monotremes?