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?

Question

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Mammary and skin glands, three ear ossicles, diphyodont, and dentary-squamosal jaw articulation are traits shared by all three groups - monotremes, marsupials, and eutherians. Egg-laying is a unique trait to monotremes, and a placenta is a unique trait to eutherians. A vertical tympanic membrane is a trait shared by both marsupials and eutherians. Therefore, the only choice that includes traits shared by all three groups is A.

Monotremes,like the Duck-Billed Platypus,are Egg-Laying Mammals (Oviparous),covered in Hair,have Mammary