Re: New alvarezsaurid

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

>        I'm not convinced. A keel might have been part of a 
cartilagenous
>"bridge" between the sternal plates. Do you have data on how strong 
such a
>structure would be, or how strong it must be to support a keel? In any 
case,
>this seems rather speculative.

    It's ( in my mind ) a sort of common sense conclusion. What would be 
stronger: two plates held together by cartilage or a single sternum?

>        Out of curiosity, which avetheropods had paried sternal 
ossifications?

    Norell and Makovicky say that two sternal plates is primitive for 
Dinosauria and the ossification of the units may be diagnostic of Aves. 
This seems to be true for Maniraptoriformes but I'm not sure about the 
condition in allosaurs.

>>     If a basal member of a group has a feature that is seen in no 
other 
>>members of the group, then it only distuingishes that genus or family 
>>only.
>        But what if two members of the group have it, and evidence from 
most
>of the others is equivocal? Nothing is as simple as it seems...

    I wish everything was as simple as it seems.


>        If snakesdiverged first from the rest of Reptilia, and we only 
had
>one fossil snake to go on, would we consider limblessness to be present 
in
>the reptilian common ancestor? You have to be careful when making 
judgements
>as to whether a basal taxon is truly underived with respect to the 
other
>members of the clade in question.

    Good point. 

>>    Actually, it has no bearing on the hypothesis. Size and shape of 
the 
>>sternum in various bird groups is extremely variable. And in early 
birds 
>>the size is smaller than that of modern birds.
>        I'm afraid you misunderstand. I merely meant that your 
statement
>about a lack of an ossified sternal carina in _Arcaheopteryx_ was in 
error,
>which may affect your interpretation of the distribution of that 
character.

 Understood.

MattTroutman

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