evolution of flight ?

You are talking about the evolution of flight with a friend. Your friend says “Birds and bats are both tetrapods. Without fossil evidence we should assume that flight evolved only once.” Explain how your friend is both right and wrong,

Update:

Using key terms like  homology, homologous structures, divergent evolution, convergent evolution, homoplasy. please HELP ASAP!!!!!

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  • 2 months ago
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    I was going gangbusters on this until you mentioned the key terms that have to be used.  I can only give a few hints, and if you copy/paste my answer, you will not get high marks.

    o My friend is right that birds and bats are both vertebrate tetrapods.  You can look at the skeletons and see the bones of four limbs with the hips and shoulders and forelimbs and hindlimbs in corresponding locations.  These limbs show "homology" and are "homologous structures," as limbs, right?

    o My friend is wrong about flight only evolving once (without looking at fossils).  Have a look at insects.  Plenty of those fly, and they're distinctly not vertebrate tetrapods.

    Check it out.  Many many placental mammals do not show any flight adaptations, nor any vestiges of that, at all.  It's a slam dunk that the common ancestor of placental mammals did not fly.  Bat flight is a later feature;  bats diverged from other mammals, and that's "divergent evolution."

    Birds are distinctly not placental mammals and do not have placental mammal ancestors.  The egg-laying is a big clue to that.

    You can also look at the anatomy of the wings.  Birds support only the leading edge with arms, hands, fingers.  Bats support the wing with arms and hands, but the fingers are spread out to support wing membrane in several additional places.  It's pretty much slam-dunk that these *wings* are analogous, not homologous, structures.  It's a "convergent evolution" homoplasy for flight.

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