# Re: Running T. rex

```Hello all,

A month or two ago I spoke with Mr. Carrano concerning Sue's speed, and that
of T. rexes.  I feel I can properly recite it for the list, with relatively
little bias.  I will be quting Matthew Carrano, these calculations are not
my own work.  I merely am the messenger.  (I am allowed to reproduce a
personal correspondence, right, as long as I don't plaigiarize?  This was
not a published paper of his I read...)

The first consideration is that animals don't like running.  T. rex would
not run if it didn't have to.  So its prey, be it dead or alive, must have
moved slower than T. rex.  Mr. Carrano stated that there were no large prey
items that could move faster than T. rex in its environment.  (I would agree
that T. rex DID hunt, but that's another story, and based on my own
reasoning-I did not speak with Mr. Carrano concerning the hunting or
scavenging)  So we must keep in mind that T. rex would not race for the sake
of speed.

Next we take the stride length of T. rex.  A step covers fifteen feet, so a
stride covers thirty.  Now we assume that T. rex could take two steps per
second, a reasonable estimate.  If so, then T. rex would move 30
feet/second, which equals 20.45 miles per hour.  This is an acceptable
walking estimate for the animal.

Mr. Carrano mentioned that, assuming no aerial phase possible, then T. rex
could speed this up slighty by either increasing the stride or taking more
steps per second, both of which are very limited.  If T. rex managed to
cover five more feet per second, by whatever method, this would equate to 24
miles per hour.  But these calculations of fastest non-aerial-phase speed
verge on the subjective.

I asked about why no aerial phase is likely in this animal.  I also
mentioned the figures from Gregory S. Paul's _Predatory Dinosaurs of the
World_ that state T. rex having similar limb structure as ornithomimosaurs,
and so bone structure would allow for an aerial phase.  Mr. Carrano told me
that not only are the T. rex limbs and ornithomimosaur limbs similar, but
they are statistically identical to each other.  He told me that the
comparison doesn't help too much though, because both animals are extinct.

Another issue he brought up was that in an aerial phase, an animal would
have to sustain many multiples of its own weight in landing (which I
question, granted momentum makes the animal accelerate to the ground faster,
but many multiples seems too excessive).  This is why the bone structure
plays the great role it does.  Could T. rex support the weight of a run?
There is no definitive answer to this.

Next is propulsion.  Could the animal move itself that fast, does it have
the muscle?  Mr. Carrano cited research by John Hutchinson that shows T. rex
as not having the adequate muscle mass in its caudofemoralis to propel
itself into an aerial phase.  Mr. Carrano stated flatly, "So could Sue run?
I doubt it, but of course I cannot prove it."

Mr. Carrano mentioned that while the speed of twenty miles per hour seems
slow, because of its stride length and size and acceleration, it is possible
to envision T. rex catching smaller, seemingly faster animals.

Mr. Carrano was very kind to have his discussion with me, and was nothing
short of professional and considerate in speaking with me.  I appreciate his
educating me.

That is about it.  I feel as if I successfully repeated this without my bias
for a running T. rex getting too involved.  If this discussion continues, I
would like to hear the opinions of more experienced members of this list,
but I'm assuming this discussion has been had repeatedly, so most people
will not be interested in continuing it.  If anyone has any views, I too