Re: New alvarezsaurid

["Matthew Troutman" <m_troutman@hotmail.com>]

><Au contraire, mon ami. Although I haven't seen the paper yet, what I 
>gather from the dinosaur list postings is that Shuuvuia (or however you 
>spell it) is a perfect example of a flightless ground-dwelling form 
>descended from a flying dino-bird. Fits with BCF precisely. The big 
>problem is just where on the bird-theropod cladogram to place it.>
>
>Double atavism. I think I'm being redundant here, saying something 
>that's been said before. But if ratites are derived from volant forms, 
>which in turn were derived from cursorial forms, then it is highly 
>likely so were the Mongolian dinobirds (and all other alvarezsaurids). 
I 
>have no probelem with this.

    Mongolian dinobirds? Do you mean the dromaeosaurs, oviraptors,etc? 
If so, there is little evidence of flying ancestors ( at least from my 
opinion ). I have trouble thinking of some of the higher groups of 
theropods as being flightless descendents of " dinobirds " or even basal 
birds because these creatures show few paedomorphic features, a trend 
that is seen modern day flightless birds. None of the postulated 
"flightless" dinosaurs show paedomorphic flightless features such as a 
vestigal humerus, large orbits, etc. Now it can be said that perhaps 
that they did not evolve these features because they still were active 
predators like in the phorusrhacid case. But, what phorusrhacids show is 
that the forelimbs would have to go through a distinct carpometacarpus 
arrangement that prohibits movement and leaves the manus parallel to the 
radioulna if they used their forelimbs for predation. Theropods, and 
espcially the "flightless" ones still have mobile wrists which are 
incongruent with forelimb function as " prey holders ". 

>But when we have a 100 million year gap between *Protoavis* and the 
>first feathered fossils (Archie, *Sinornis,* etc.) this is either 
>attributable to ghost taxa (all too likely, considering the 
>champsosaurs) or that we have some really wierd archosaur (and who 
>knows, Greg may be totally right in postulating in PDW that he was a 
>herrerasaur, therefore a dinosaur, and that may be *Protoavis'* 
>cladistic placement).

    Protoavis is certainly enigmatic. An interesting thing about 
Protoavis is that its braincase features ( fenesta pseudorotunda, inner 
ear structure ) are not unique among Triassic creatures, they are also 
seen in crocodylomorphs. I am surprised Larry Martin did not ever ( at 
least to my knowledge ) bring this up. Regardless, Protoavis should be 
studied more so we can tell whether or not it is a dinosaur, bird, 
crocodylomorph, or chimera. ( And please note that I believe that I 
believe the BAMM, _ Birds Are Modified Maniraptorans_, theory and not 
the crocodylomorph theory).

>The case is open, with both sides having their qualifying points, so 
I'm 
>going to be the good little scientist and wait. (Actually, I'd like to 
>see the rest of *Protoavis'* skeleton.)

   Check out Chatterjee's book.

MattTroutman

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