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Re: Diplodocus: Return to the Swamps????

>> You seem to miss the reality of
> > a swamp; sooner or later you _sink in_ no matter how
> 'spready' your feet are. At which point,
> > 'spready' feet are a serious _disadvantage_. Swamps
> often have sharp sticks, logs, even rocks
> > that can function as impalers or entanglers. If the
> area has a bottom you can reach, you WANT
> > compact feet that slide easily to it, and then
> _retract_ easily.
> Theropod feet spread on the way down, but fold up into a
> nice compact narrow shape on the way 
> back up. The spread foot makes it more difficult to sink
> into the mud to begin with (and less mass 
> doesn't hurt either). The more compact retracting shape of
> the foot means it's easier to extract it 
> from the mud than it was to push it in.

Spread toes are vulnerable to injury in deep mud when you weigh several tons. 
"...sharp sticks, logs,..."

> > And less power...
> Mass isn't necessarily a good measure of power. In fact,
> I'd go as far to suggest that theropods 
> had a greater proportion of locamotive muscle mass than
> sauropods had. A biped needs leg 
> muscles to actively keep it upright. A quadruped just has
> to lock up its leg joints when its not 
> moving, and it turns into a passive table. 

That is relative power. Mice have very high relative power, but cannot break 
free of a sticky trap... absolute power is what is needed in mud. Sauropods had 
the mass AND the leverage.

> >  ...When you are up to butt in mud, you have no
> worries about that...
> I'm not envisaging regularly moving through crotch-deep
> mud, since no sane animal would do that 
> very often. 

Nothing insane about being theropod-free when you have a long skinny neck and 
tons of tasty meat. Not to mention being thermally stable. Takes the weight off 
achy feet, too. Reach up, nip a few leaves, go back to sleep...

Big old mud-bug could have a good life.

> Rather, I'm suggesting that large theropods did
> better than sauropods on slippery 
> ground with no more than ankle-deep mud - something most
> dinosaurs would have encountered at 
> some point (as evidenced by trackways).

Certainly there was theropod-friendly terrain, and sauropod-friendly terrain. 
But what you describe is not a swamp by any definition I know of. Swamps, btw, 
don't preserve tracks per se, barring possible underprints...