Re: New alvarezsaurid

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

>Now suppose that the keel >did< evolve for flight, in a small, volant
>theropod, and was retained by at least one of the descendant lineages 
of this
>small theropod--the lineage that led to the allosaurids. Then we don't 
have to
>imagine an allosaurid trying to take off using its arms in order to 
account
>for the presence of a keel on its sternum. (The keel is not 
particularly well
>developed--it's about as prominent as the keel on the sternum of 
_Mononykus_.
>And we all know what the keel means in _Mononykus_, right?)
>

    It could have evolved in the allosauroid ancestor ( or even in 
allosaurs themselves ) for many reasons: climbing, prey handling, 
fighting, etc. 

As for alvarezsaurs, it could have been a holdover from volant 
ancestors, or could have been lost and regained for the same reasons as 
allosaurs. 

The presense of volant adapations is not direct evidence of volant 
ancestors. Take Longisquama, it has a furcula, but I think that it is 
clear that it is not a flightless descendent of volant ancestors. 
Basically in allosaurs and other theorpods with volant adaptations, you 
see no paedomorphic characteristics. Paedomorphic changes are always 
seen with the loss of flight.

MattTroutman

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