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Re: Airbagged(was Dive!Dive!Dive!)



On Tue, 5 Nov 1996, Jeffrey Martz wrote:

> Rob Meyerson wrote:
> 
> > If I recall from when we had this discussion last year, someone mentioned
> >  that when an ostrich stumbles, it orients its body so it will land on it's
> >  side.   When it hits the ground, it expends the excess inertia by
> >  continuing to roll across the backbone, and onto it's other side (where it
> >  could easily get back on it's feet).  Perhaps T. rex used a similar
> >  strategy.  Twisting it's body sideways and rolling over it's spine to
> >  prevent a fatal fall.

        When I said that T. rex might "catch" itself, this is more along
the lines of what I was thinking. People catch themselves with their arms,
but prevented use of arms, I would assume that people would try to catch
themselves by landing on the shoulders, NOT smacking their faces into the
ground. It's what I'd do, anyway. T. rex's arms were relatively
small, although in absolute terms quite large and heavily muscled, and
perhaps not _completely_ useless in such a situation, but perhaps the
extremely large scapulae of T. rex were for exactly such a
shoulder-landing? Anyone who knows much about sports (not that I'm such a
person, but my brother was a wrestler) has probably learned that you have
to learn to take your falls. ( there's a reason cats land on
their feet!). T. rex might have been able to to pull its head back so that
it did not impact the ground, and the tail could have been very useful as
a large mass to push against and direct the motion of the body. This does
not, of course, eliminate the problem- there's a breaking point to bone
and certain laws of physics that T. rex can't escape, but it may have
allowed somewhat higher speeds than what Farlow has calculated. 
        I've come to accept that the thing probably ran at less than
Bakkerian speeds, but I still think it may have been quite fast for it's
size, faster than an elephant, perhaps.
        The reason I was asking about cortical bone is because I was
wondering if the formula takes into account it's placement. A given amount
of material resists breaking much better when formed into a tube than a
rod, and it may, or may not, be that T. rex differed from elephants in
this respect. The amount of bone is not the only factor- certainly,
pterosaurs were using very, very little bone in their big humeri, but they
were quite strong. 
        As for living in forests, this generalization may not
be accurate. Different animals can live in many different environments-
someone mentioned to me once (was it here?) that the East Coast forests
used to have BISON in them. I would be surprised to learn that T. rex was
not a widely ranging animal, and it may be that these environments were
forested to varying degrees. I believe that wolves sometimes prowl
forests, but are also known from wide-open spaces up in the Arctic, bears
may live in forests or may live where not a single tree is to be found
(and I know this from experience ;) having seen them in one, and run 
into them up close in the other). 
        I think that femur strength and falling are very convincing
arguments for lower T. rex speeds, but while they're a significant step
forward in figuring out how they moved, I don't think they're the end of
the story. I shouldn't hide the fact that I am very biased for high-speed
rexes, but I'm kind of cooling off a little and taking more of a look at
slower speeds. But the limb proportions are simply nothing like what you
see in an elephant or sauropod. The thigh bone is much shorter, the
metatarsals, much longer. This may still be due to fleet-footed ancestors,
but it doesn't look like a graviportal animal. And don't forget the bears,
which can run quite fast! I'd be interested in knowing how the
calculations for those work out.

        nick l.