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RE: Polyphyletic

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Posted by: CKing at Thu Oct 2 12:29:16 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  
   

>>Sorry for being vague. By "limb", I mean a limb comprised of a humerus, radius, ulna, etc... with or without some parts fused or lost. If we are grouping things using symplesiomorphies, this should work fine. Please re-evaluate my grade.>>

Sorry, your new answer is not any better. The limb bones of tetrapods are derived from fish, so your "limb" now would include the fins of some fishes. "Limb" (per your definition) is now a symplesiomorph of a more inclusive group than tetrapods. Even if we restrict your new definition of "limb" to tetrapod limbs, we end up with Tetrapoda, not your nameless taxon of frogs plus birds. That is because a paraphyletic group must include all organisms that possess that symplesiomorph, not just some. You can exclude snakes and legless lizards and other limbless vertebrates from a paraphyletic group, defined as having "limb comprised of a humerus, radius, ulna, etc..." because the limbless vertebrates have evolved a new character state: loss of limb. But you cannot exclude other tetrapods from this group because they still have limbs. "Limb comprised of a humerus, radius, ulna, etc..." is not a symplesiomorph or synapomorph of frogs plus birds. It is the sympleisomorph of a more inclusive group.

Therefore even if you were allowed to retake the test, your grade remains an F.


   

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