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Re: A fundimental conundrum concerning gigantic theropods



Dinogeorge writes;

>Then why are the fastest extant terrestrial animals all quadrupeds? Gazelles,
>antelope, and cheetahs beat ostriches and smaller running birds and kangaroos
>for sure. This business about bipedality evolving >as an adaptation for
>increased speed< is too simplistic. Gotta look at physiology, stance,
>behavior, everything, not just speed. Almost all extant bipeds are highly
>derived animals with long evolutionary histories in which their bipedal
>stance has been exapted for all kinds of purposes, including but not limited
>to high-speed running. The question is, Why did they get up on their hind
>legs the >first< time? Maybe just to have a look around, or to intimidate a
>rival, or to mate, or to climb a tree. No way to choose among lots of
>plausible alternatives.

I don't mean to imply that speed is the reason for why things become
bipedal.  Personally, I would be rather skeptical of such a theory.
For the record, I have tried to keep most of my suggestions based on
the increased manuverability of the bipedal form.

As far as for how bipedalism evolved, I suppose there are as many
reasons as there are bipeds.  [For us, bipedalism appears to have been
an advantage for savannah living (or lagoon living, if you prefer).]
My point is that once the critter has become a habitual biped, it will
"discover" the greater manuverability of the new form, and the
advantages that go with it.  This "discovery" will give the animal an
edge in survival.

Finally, the reason why there are no extreme-speed extand bipeds is
because none of todays bipeds have a reason for it.  Ostriches feed on
small rodents and the like (things that aren't very fast to begin
with), and are preyed on by the biggest cats, which also are not known
for being speed demons (I don't think I've heard of cheetahs going
after an ostrich).  Therefore, the need for speed is not as crucial as
it would be in something like Utahraptor (an animal with the potential
for high speeds).

Rob Meyerson
Orphan Vertebrate Paleontologist

***
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