Re: Sloping terrain Re: Woman against Abelisaur

[Don Ohmes <d_ohmes@yahoo.com>]

On 7/25/2011 3:34 AM, David Marjanovic wrote:
> It would be that way if all else had been equal. But it wasn't.

True.

> The
> theropods had long, somewhat spreading toes; such feet don't sink in
> easily,

True again, but we are considering the case where sinking occurs, are we 
not?

> but are easy to pull out because the toes taper and can be
> brought together.

I have doubts about this model -- after all, the tridactyl foot 
logically has a much greater surface area per unit available power than 
the columnar one, and I question the idea that the 'drag profile' upon 
w/drawal is actually lower in absolute terms.

Further, consider a substrate wherein the overlying seds yield very 
easily to a depth of 1m, and then adequate footing is found -- in the 
event that the toe-tip catches on a root or rock while in transit to the 
bottom, you now have a short lever under great downward pressure -- if 
the root or rock does not give way, the toe might. If the underlying 
'bottom' is also uncertain, as most are, problems can easily begin to 
cascade.

In any case, the biped now is both at risk of injury, and/or on uneven 
footing, therefore unstable.

Again, the human body gives a chance to experience the reality -- push 
your open hand into soft mud and w/draw it -- then try it with closed fist.

The quadruped w/ columnar feet has no such problems. Splayed toes do 
help to prevent sinking, but once sinking occurs, they are a liability.

> All sauropods had compact feet and outright columnar
> hands that must have sunk in easily and must have created suction when
> pulled out.

At the risk of creating 'collateral humor', I have to state that suction 
is highly over-rated.

In most seds, wiggling a limb embedded in mud creates low density zones 
immediately surrounding the limb -- and (again, in most seds) these 
zones are temporarily filled w/ watery fluids that are less solid than 
the surrounding substrate.

In the unusual cases wherein solid components immediately rush in to 
fill the void, I assert based on personal observation that columns are 
easier to w/draw than splayed toes, even if the toes do 'fold up'. This 
concept, at least, can be thoroughly tested w/ mechanical models.

Lastly, a quad w/ columnar feet can apply much more withdrawal force per 
limb than a biped w/ tridactyl feet. More stable platform to pull from, 
more power per limb, and lower surface to power ratio...

The intuitive 21st century perceptions just do not work when examined 
closely.