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Re: Triassic dinosaur evolution



> Mammalian hearing bones are more advanced, no? is the quadruped
>bauplan of a cat (tigers, sabercats, etc) better than a biped
>predator?

Probably all this is obvious to anyone here, but since noone is saying
anything along this lines...

Note that there is a crucial difference in the bauplan that makes a
quadruped dinosaurian runner less like, if I understand things
correctly: Somewhere in their evolutuion mammals changed their
backbone movement from left/right to up/down. Thus a cheetah gets some
part of its speed from this movement which was (please correct me if
I'm wrong here) not available to theropods.

So evolutionary constraints may simply make it less easy for dinosaurs
to become quadrupedal runners.

BTW, backbone movement is also the reason why whale fins are
horizontal, but ichthyosaur (not dinosaurs, I know) fins are vertical.

> It allows a lower profile when sneaking up on prey, cheetahs show us
>it can be every bit as fast or faster than a biped (cheetah >
>ostrich), so aside from freeing the forelimbs (which humans and birds
>made good use of), what good is a bipedal stance?

Well standing higher may also have its advantages as it allows to se farther. 



> Im surprised the Dinosaurs did as well as they did - size
>constraints suggest a quad predator could become larger than a biped
>predator, would be more "sure footed", and wouldn't have a large
>portion of its mass serving only as a counter balance.

OTOH, it only needs two big muscle groups instead of four - the fact
that fast runners are all in the same range of speeds (say 80km/h or so) may 
imply that there is not much advantage either way.

Martin.

                   Priv.-Doz. Dr. Martin BÃker
                   Institut fÃr Werkstoffe
                   Technische UniversitÃt Braunschweig
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