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Re: the birds and the crocs



 From: John Alroy <jack@homebrew.uchicago.edu>
 > 
 > In response to two points in Stan Friesen's latest:
 > 
 > > I do not know of any large crocodilian that actually *spans* the
 > > boundary.  The largest crocodilian ever dies at or near the
 > > boundary (Leidyosuchus, aka Phobosuchus).
 > 
 > Um, I thought this sounded a little strange because I've seen  
 > Leidyosuchus in many early Tertiary faunal lists. Turns out that  
 > Carroll (1988: Vert Paleo and Evolution) lists Leidyosuchus as  
 > ranging from Late Cretaceous to Eocene, and furthermore identifies  
 > Phobosuchus as a junior synonym of Deinosuchus, which is restricted  
 > to the Late Cretaceous (is Deinosuchus what you meant to say?).

Oops, you are probably right.  I knew Phobosuchus was now considered
a junior synonym of *something*, I just got confused as to what.

[Hmm, how big was Leidyosuchus?  My guess would be caiman sized,
but I am not sure].
 > 
 > > Apparently the small theropods ("coelurosaurs") could
 > > not compete effectively with birds, and lost out to them about
 > > the middle of the Cretaceous, if not sooner.
 > 
 > What makes you think that? 1) Birds fly; 2) Even the smallest  
 > coelurosaurs ("size of a large dog") would have been several orders  
 > of magnitude larger than the average bird;

The smallest "coelurosaurs" prior to birds being common were
chicken to turkey sized (perhaps even smaller).
[Check out Compsognathus].

 > 3) Most birds aren't  
 > carnivorous, they're granivorous, insectivorous, or frugivorous.
 >
Most small theropods were also probably insectivorous.

And most of the granivorous and frugivorous lineages of birds
are more derived, which combined with Archaeopteryx and the
other toothed birds, suggests that the original birds were small
carnivores and insectivores - which is exactly what the Late
Jurassic "coelurosaurs" were.


I find it very telling that Compsognathus sized "coelurosaurs"
dissapear rather shortly after the evolution of birds.  (Unless
you actually believe Chatterjee is right about Protoavis ...).

[Actually, some very specialized small forms, like Oviraptor,
continue into the mid to late Cretaceous, but even these were
gone by the Latest Cretaceous - to leave only mid-sized forms
like Troodon, or larger].

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.