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

[Dann Pigdon <dannj@alphalink.com.au>]

On Mon, Dec 14th, 2009 at 1:11 PM, don ohmes <d_ohmes@yahoo.com> wrote:


> Wrong. Mud that a theropod would sink up to it's crotch in would render it 
> nearly immobile, and
> quickly stomped flat as a fritter by the longer legged sauropod. 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.

> > Theropods probably also had less density than sauropods,
> > never mind the fact that they usually 
> > had less mass in an absolute sense. 
> 
> 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. 

>  ...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. 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).

-- 
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Dann Pigdon
GIS / Archaeologist                Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj
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