Monotremes, like the duck-billed platypus, are egg-laying ma…
Monotremes, like the duck-billed platypus, are egg-laying mammals (oviparous), covered in hair, have mammary and skin glands, three ear ossicles, are diphyodont (their permanent teeth replace their “baby” teeth), and possess dentary-squamosal jaw articulation (the jaw bone hinges with the squamosal bone of the skull). Marsupials, such as kangaroos and koalas, are pouched mammals that have a vertical tympanic membrane in addition to being covered in hair, have mammary and skin glands, three ear ossicles, are diphyodont, and possess dentary-squamosal jaw articulation. Eutherians are the placental mammals that most people easily recognize as mammals. They are covered in hair, have mammary and skin glands, three ear ossicles, are diphyodont, possess dentary-squamosal jaw articulation, and have a vertical tympanic membrane. What traits are shared derived traits for monotremes, marsupials, and eutherians?
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