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Lecture 6 ANIMAL EVOLUTION: THE VERTEBRATES. Three Lineages of Mammals. (monotremes) egg-laying mammals (marsupials) the pouched mammals (eutherians) placental mammals. Monotremes : . The only egg-laying mammals
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Three Lineages of Mammals • (monotremes) egg-laying mammals • (marsupials) the pouched mammals • (eutherians) placental mammals.
Monotremes: • The only egg-laying mammals • Egg; reptilian structure contains yolk to nourish the developing embryo. • Have hair and produce milk. • Mixture of ancestral reptilian characteristics indicates monotremes descended a very early branch in the mammalian genealogy. • The platypuses & anteaters