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Re: large body size vs little dinos



 From: Flyinggoat@aol.com
 >      But what about the small-body mass dinosaurs?  Like Troodon,  or
 > Velociraptor Mongolensis?  We know that crocodilians survived the extinction,
 > and crocs can get much bigger than any recorded find of either of these two.

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).

What appears to have happened is that the large ones died, and then
new large forms re-evolved later.

 >   I may not be familiar with other types by name, but after 165 million years
 > of a dinosaur age there statistically had to be dinosaurs of small body mass,
 > like Hipsephaladon, but from the Late Cretaceous.   Where were the dinosaur
 > non-specialists?

Most of the small dinosaur types, except the protoceratopsids,
pachycephalosaurs, and troodontids had already died out long
since.  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.

Of these, only the protoceratopsids can really be said to be
generalists, and they seem to have been fairy rare (at least
there are not many specimens in the Late Maastrichtian beds).

The most thorough generalists left, the ornithomimids, were
both rather large and quite rare (probably rarer than proto-
ceratopsids).  So, since small population size is also a risk
factor, all of the remaining dinosaurs were in high risk categories.

 > Its the same law as the one about the number of books you
 > own will always be greater than the places you can put them, dinosaurs were
 > around so long that they had to evolve into every available niche.

Not so.  Many niches, especially those of the *small* generalists,
were, by the Late Cretaceous, filled by mammals and birds.

Think about this - Troodon was apparently the *smallest* dinosaur
during the Maastrichtian (the protoceratopsids were probably
heavier).  And *it* was the size of a large dog.

Everything smaller than the 100 lb. limit for animals ecologically
"small" animals was either a bird or a mammal.

 >    Its that genetic diversity thing again.  Unless the non-specialists were
 > out-competed by the mammals and birds in an earlier age, and replaced by
 > them. I'll give you that the small non-specialist dinosaurs could have
 > already been extinct at this time. 

They were.  No dinosaur clearly less than 100 lbs still existed.

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

The peace of God be with you.