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Re: Long-necked stegosaur (the reason for long necks?)



--- On Sun, 3/8/09, Jonas Weselake-George <paleo@ncf.ca> wrote:

> For adult members of the largest species one can definitely
> imagine issues emerging in a variety of situations. A sixty
> ton animal would require upwards of twenty tons on each of
> the three feet remaining on the ground (and the actual
> weight on some of the feet would be higher due to uneven
> distribution). The surface area which is in contact with the
> ground is alarmingly small. 

True, but not as bad as it seems. Most muds are a mix of solids (typically w/ 
some sand) and fluids. Once a foot is large enough to move the water and, uh, 
'oozier' elements aside, yet compress the solids (which are limited in lateral 
migration distance) what is left below the foot is essentially a column of 
sand. At this point, the yield stress number rises _sharply_.

In the 'bottom-less' case (a deep pool of uniform fluid): a large animal will 
'notice' a given viscosity less than a smaller one. Whereas pancake syrup might 
shut down a mouse or even a cat, an elephant would barely notice it...

Both of these cases are testable.

> The really interesting thing is that large sauropods have
> to deal with physical heterogeneity at a larger scales than
> most other animals. Being able to move feet to ideal
> locations before putting them down could be a real advantage
> (and having to find firm footing for all three feet could be
> impossible in some environments - even if there are secure
> places to put down a couple of them).

Not a problem if you are belly-deep in mud... :D. Heh. Sorry.

> It would be interesting to try to make estimates regarding
> the maximum height of a vertical obstacle that could be
> cleared, the maximum length of trench that could be stepped
> over and the maximum feasible radius within which a foot
> could be placed (without moving the body as well).
> Preliminary estimates should be possible for these areas
> using only the articulations of the bones (ie. avoiding
> potentially dodgy estimates of muscular force and joint
> strength).

Seems useful. Probably been done? Don't know, tho...

> The important point is that we should stop assuming that
> sauropods could easily plow their way through any forest.
> Even if I weighed sixty tons I'd think twice about
> knocking down a ten ton tree. I've seen enough people
> injured from trying to pull up saplings to imagine all sorts
> of ways that could go wrong... 

Well, it would depend on tree species and soil conditions, as well as tree 
size. Some stuff would be pretty easy. Where it is wet, root systems tend to be 
more limited, for example.

Back to necks; in my view, no animals have ever been better suited for chugging 
through deep swamps than sauropods, and long necks fit well in such a scenario. 
I note that few would agree w/ me, at least publicly, and know of no way to 
conclusively test this view. It would be interesting to know if sauropod necks 
show sign of being adapted to resist upward or posteriorly directed pressure, 
such as would occur if a sauropod was moving through very deep mud.

I also see no reason to think that the stegosaur in question was a 
swamp-dweller, am sorely lacking in time and so turn this thread over to the 
tender mercies of others, including those who argue that sauropods spent their 
days galloping through the countryside, necks as straight as flagpoles, 
vaporizing theropods w/ their tails, while flinging them like ragdolls w/ off 
of those mighty necks and avoiding mud like the plague. If there are any of 
those guys left...

And why do they seem to all be guys, I wonder?

Don