large theropod body config and predation

[dunn1@IDT.NET]

OK, another big theropod question.

What 's the current theory about the differences between the body 
forms of the Carcharodontosaurids and the Tyrannosaurids?  Armed only 
with the dangerous weapon of "common sense," and a little reading,  I 
have intuited the following:

1) Car'ids were an evolutionary response of  allosaurids to 
increasing size in sauropods, and as such they pushed the frame to 
its limits, resulting in shorter legs to sustain the heavier weight.  
The heaviness decreased the likelihood that a Car'ids would be badly 
injured while approaching sauropod prey.  They continued to benefit 
from the blade-like teeth of the allosaurs because, despite their 
increased size, they were unable to bite into and hold  a 
sauropod in their jaws without a very good chance of being 
rendered two-dimensional.  

2) Tyrannosaurs developed because of the decline in numbers of the 
sauropods in the dinosaur fauna of Asia and North 
America; remaining large prey species were somewhat faster than 
sauropods had been, and Car'ids were unable to cope.  Coelurosaurs 
exploded into the empty large predator niche, rapidly developing what 
they needed to prey on large herbivores (thus explaining the 
forelimbs, which got left behind, so to speak).  The result: fleeter 
large predators with the longer legs of Coelurosaurs and teeth like 
railroad spikes rather than steak knives, with an emphasis on biting 
and crushing rather than slashing and retreating.

I'm sure there's plenty wrong with this analysis, which is why I'm 
posting it.  I'd welcome comment. Please comment on brain size 
differences as well; I assume the Tyrannosaurs benefitted from larger 
brains because they were Coelurosaurs, the bunch formerly 
smaller, and who thus had to be smarter (or otherwise better equipped 
to sort out sensory data).

Thanks,
Larry

"We are Pentium of Borg.
Arithmetic is futile.
Prepare to be approximated."

--from Intel, the Next Generation