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Mission Impossible 2F (was Re: New dinosaur articles)

Tracy Ford wrote...

>…On the other hand, it must be pointed out that cladistic result is based on the assumption of the principle of parsimony >which is, however, philosophically untestable...in other words, theoretically there is no single dinosaurian character in >Caudipteryx that could not have been reversed from its presumable avian ancestor…

    Testing if Caudipteryx is plesiomorphically cursorial (according to parsimony) should be no more "philosophically untestable" then if it is secondarily cursorial, although it would require committing the ultra-strict cladism no-no of considering interpretations about functional morphology.  Phylogenetic analysis with parsimony is a good enough starting point from which to start tweaking around with the tree using functional inferences to see what sort of changes you get.

    Greg Paul's idea that a cursorial lifestyle in dromeosaurs is secondarily aquired, and that flight originally evolved lower down within Coelurosauria, may receive wider consideration within the professional field then people realize.  I have heard at least a couple well-known professionals say they toy with the idea, although they are waiting for more fossils.  The "predatory snap" theory for the semi-lunate carpal always seemed awfully ad-hoc to me, as did the idea that Unenlagia being able to swing its arms out straight sideways was an adaptation for balancing when running.  I think what really got me taking it seriously was the pygostyle in the oviraptid.  You can only pile on so many features which are known to be adaptive for flight with ad-hoc explanations for how they might have been preadaptive (rather then secondarily retained) in a cursor, before it starts getting suspicious.  Secondarily flightlessness being as common as it is within birds, there is nothing all that extraordinary about secondaily flightless coelurosaurs being tossed off in the early days before a lot of the specializations had even evolved.  However, Dinogeorge's add-on to Paul's idea, that there is significant evidence flight and arboreality controlling theropod evolution all they back into the Triassic, is in my opinion still pretty weak.

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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
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