T. rex limitations

["Colette H. Adams" <cadams@hh.gpz.org>]

The large size of T. rex is not "adaptive" for concealment, any more than
the large size of a Siberian tiger is adaptive for concealment.  It is
adaptive for feeding on large prey items.  Those who have a hard time
envisioning how a multi-ton animal can hide itself should spend some time
at the zoo.  I frequently am amazed at how difficult it can be to spot
elephants, giraffes, and rhinos in relatively sparse enclosures in which
you KNOW they reside.

It seems fairly obvious to me that tyrannosaurs have cursorial adaptations.
 Coombs classified them as "subcursors," comparable to dogs.  Others have
argued that they were in fact good runners.  It seems to me that the big
picture is being lost to some extent in the fine details.  Komodo dragons
use ambush to inflict wounds on cursorial mammals whose ability to
accelerate and sprint far exceeds them.  How?  By being very stealthy.  It
is no great miracle.  Canids use "pursuit and bite" to kill animals with
superior cursorial adaptations.  How?  By working in groups and having
superior stamina.  Again, no big problem.

We seem to have all these arguments trying to show in one way or another
how T. rex is inadequate to the task of predation, particulary on
ceratopsians.  It is too small, or it is too large.  Its bones are too
thin, or its claws are too blunt.  Its jaws are too weak, or its teeth are
too fat.

If we look at the skeleton of T. rex, with its "poorly designed" limb
joints and "weak" bones, we might easily come to the conclusion that it
could never walk, because walking leads to inevitable trips, and trips
require you move your foot under you speedily and support your entire
weight on it (even more if you have tripped badly).  But we have so much
evidence that it DID walk that such a conclusion is untenable.  Since we
know it had permanently flexed knees, we know we are not talking about the
simple resistance of bone to compression or shear.  There had to have been
very powerful muscles, which implies strong bones and joints.  If we have
to invoke a thick perosteum or strong joint ligaments to keep the structure
together, fine.  But it is no use saying the bones are too weak, or the
joints are too poorly made, to allow the animal to do what we KNOW it has
to do.

Could T. rex run?  I think so.  But if it didn't need to, it didn't.  I
remember reading somewhere (Horner's book I think) that T. rex's limbs were
constructed in a way that made it "primarily a walker, not a runner."  What
does this mean?  Is there some animal that goes through life in a run?  If
T. rex needed a suspended phase in its gait to catch its prey, it had it.
If it needed to run more like an ostrich than a duck to catch its prey, it
did.  But the way to approach the problem, it seems to me, is to start with
the context, the biology of the animal and its prey.  The biomechanical
aspects are interesting but we should be very cautious about putting limits
on the animals because of the way their skeletons are constructed.  Without
the soft tissues it is easy to jump to unwarranted conclusions.

While we're on the subject, tyrannosaurs are well designed for
stealthiness.  With just the tip of its snout reaching an animal trail, we
have to search about 20 feet back to find any part of the T. rex that is
within 8 feet of the ground.  Retracting its neck, the T. rex is poised to
swiftly strike forward and downward as a ceratopsian or hadrosaur passes
without even moving its legs significantly.  It has not escaped my notice
that a few ornithiscian skeletons show signs of dorsal wounds.

Best regards,

Dave