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2005_campbl34b - Chapter 34b Vertebrates(mammals Mammalia...

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Chapter 34b: Vertebrates (mammals)
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Mammalia Though mammals predate the dinosaurs, it was only once the dinosaurs were mostly gone that the mammal adaptive radiation began in earnest The defining features of extant mammals are their hair, mammary glands, larger brains, extended parental care, differentiated teeth, modified jaws, etc. The mammal lineage predates the mammals with the synapsids: the mammal- like reptiles
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Various Synapsids
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Non-Reptilian Jaws
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Recall: Synapsids
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Temporal Openings: Jaw Muscle Attachment Anapsid: No hole in skull! Synapsid(?): One hole in skull! Diapsid(?): Two holes in skull! Euryapsid?
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Well Differentiated Teeth Differentiated dentition All teeth ~same
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Mammals: Monotremes
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Monotreme: Echidna Fertilized eggs become covered with a shell and are then laid, which the echidna then carries around in a pouch
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Monotreme: Platypus Duck-billed platypuses are aquatic so keep their eggs warm in burrows until hatching
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Mammals: Marsupials
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Marsupial Reproduction Both the marsupials' ovaries produce eggs, and they have a double womb. Once fertilised, the egg spends between 12 and 28 days in the womb, feeding from a yolk sac and absorbing nutrients secreted by the womb lining. “The youngster is then born in an embryonic state, with only the front limbs developed. It attaches to one of the females' nipples, which are often surrounded by a protective flap of skin forming a pouch. The teat swells slightly in the youngster's mouth so that it stays firmly in place, and there it stays, growing… “Marsupial mothers put very little into producing their youngsters at first, and can quite easily expel them from the pouch if they are pursued by a predator or conditions become difficult… ” http://www.bbc.co.uk/nature/animals/mammals/explore/marsupials.shtml
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Examples of Marsupials
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Mammals: Eutherians Eutherians are the placental mammals, i.e., the majority of mammals are eutherians
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Euterian Reproduction Placental mammals have a single womb into which eggs are shed from both ovaries. Once fertilised, the egg remains in the womb and a placenta develops. “This organ allows the embryo's and the mother's blood to pass so close to each other (without mixing) that nutrients and oxygen can pass to the developing youngster from the mother and she can absorb its waste products.
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