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T. rex

Some comments on recent discussion of T. rex feeding habits:

Why have all the comparisons been with modern mammals and
birds? Is it taken for granted that dinosaurs had a mammalian
type physiology?  Even if you accept this (which I don't,
preferring the ectothermic inertial-homeothermy hypothesis)
they were endothermic reptiles, not mammals.  So, why not
include modern reptiles in the discussion?

Large reptiles such as crocodiles, freshwater turtles and
monitor lizards are true carnivores, but are also accomplished
scavengers, and carrion can be a major component of their
natural diet.  Cannibalism is also common.  Of the other large
reptiles, lizards other than monitors are largely herbivorous,
sea turtles are specialised feeders and the snakes are a bit
of a mystery.  Snakes probably rarely eat food they have not
killed themselves, but it is unusual to observe them feeding
in the field.  In captivity however, with very few exceptions
they readily take dead food - they probably don't get the
opportunity in the wild.  So large carnivorous reptiles
generally scavenge opportunistically.  

All reptiles which feed on vertebrate prey consume and digest
the whole animal, including bones - they have a high
requirement for dietary calcium.  None of them remove the
flesh from the bones.  If dinosaurs were similar, there would
be nothing left after a kill for a specialised scavenger (i.e.
the vulture niche would not have existed).  The modern
Serengeti may be a very poor model for Cretaceous ecology.  

I don't think continuous tooth replacement is any indication
of diet or behaviour - it is virtually universal in modern
diapsids except for those which are secondarily toothless,
such as turtles and birds.  I understand that the strongest
morphological argument for T. rex as a predator is the
reinforcement of the skull and neck, apparently to withstand
the impact of hitting prey at full speed with open jaws.

I would not have any problem with large adult sauropods and
ceratopsians being immune from T. rex predation (stegosaurs
are irrelevant, as they were not contemporaries), just as
elephants, rhinos, hippos, and large modern reptiles are free
from predation.  Young sauropods etc. are a different matter -
I can envisage T. rex charging a herd and snatching an
unguarded juvenile.  Why else would sauropod footprints
suggest guarding by adults?  Hadrosaurs are a better candidate
for a standard prey item - they were abundant and relatively
defenceless if taken by surprise.  It has been reported that
the currently impounded female T.rex skeleton (Sue) contained
hadrosaur remains in the stomach cavity.  Did anybody get a
chance to examine these remains?  They might show whether Sue
killed her own last meal. 

(Incidently, I have also heard that Sue had a healed fracture
of a hind leg - can anybody explain how a large biped with
mammalian endothermic metabolism could survive long enough
without food for such a serious injury to heal?)