Re: Quo vadis, T. rex? [long]

[Jeffrey Martz <martz@holly.ColoState.EDU>]

> The two scenarios you outline above are not parallel.  Tyrannosaurs and 
> dromaeosaurs are rather different critters (more scientifc jargon).  Toe 
> claws are not the only things keeping dromaeosaurs out of the 
> tyrannosauridae.  The two taxa are also roughly coordinate.  Birds are a 
> *subset* of dinosaurs, barred only by their flight adaptations from being 
> universally considered such.

     I admit it was a crappy example.  A better one would have invloved the 
segnosaurs and thier questionable affiliations.
 
> The same argument could just as easily be 
> used to separate bats or whales from the rest of the Mammalia, if all 
> terrestrial mammals were to die off and all we had were their fossils.  
> Yet that is not the way we classify them.  Bats and whales are merely 
> two examples of the broad spectrum of mammalian adaptation, just as birds 
> are merely an example of the broad spectrum of dinosaurian adaptation.

     We have living, breathing bats and whales.  We don't have living 
breathing dinosaurs to compare to birds, so determining with certainty 
that birds and dinosaurs shared a physiology is not possible.  
Pinpointing the point at which endothermy evolved in the bird 
lineage is no more possible at this point that pinpointing when 
feathers evolved.  
     There is at least some indication that there were 
differences.  Birds occupy a size range that extends below that of the 
smallest dinosaur.  Birds survived the K-T extinction, while dinosaurs did 
not.  Feathers are known for birds, while scales are known for at least 
some dinosaurs.  Endothermy is known for birds, while the indications of 
endothermy (or at least what we would call endotermy in modern birds and 
mammals) for dinosaurs is questionable.  Uncertainties are great, and 
there are at least slight indications of important differences.  
Seperating them is the safest bet given what is known. Being able to include 
birds in with the dinosaurs the way we include modern bats and whales with 
the mammals would be nice, but the fossil record does not allow it.    
 
LN Jeff