Re: Bird vs. theropod dinosaur tracks/trackways

[smithjb@sas.upenn.edu (Joshua Smith)]

Dinogeorge@aol.com wrote:

> <<  I have seen theropod trackways that "waddle" in the Early Mesozoic 
>  on the east coast.  Hithcock's opinions aside, I think most of us feel 
>  that those tracks are not "birds." >>
> 
> And how do we know these >aren't< tracks of birds?
> 

        Oh we don't.  It is an a priori assumption, agreed upon by every 
ichnologist or paleontologist that I know of that has ever seen these 
footprints, that they are theropod rather than bird, thus why I said 
"most of us feel that those tracks are not 'birds.'"  This is based, as I 
understand it, entirely on the fact that we have no avian body fossils 
from the Hettangian or lower in the Newark Supergroup, never mind avian 
body fossils that are morphologically similar to these ichnogenera.  It 
does not necessarilly parallel reality.  
        However, since it has been acceptable (i.e., has been published 
in a peer reviewed journal) to say that a large cf. theropod footprint in 
the Maastrichtian of New Mexico is a _T. rex_ track simply because we 
don't have an osteological genus in those rocks large enough to make this 
track that ISN'T _T. rex_, then I don't feel too bad just agreeing with 
everyone else in assuming that these cf. theropod tracks in the Newark 
Supergroup are probably not avian in origin, rather than devoting a lot 
of energy towards trying to figure out a way to test this assumption. 


-- 
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Josh Smith
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