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Re: Sloping terrain Re: Woman against Abelisaur



On 7/25/2011 11:55 AM, Habib, Michael wrote:

However, even taking the concept that elephants are "mud adapted",

They are 'mud competent', which makes my point -- large animals can do well in the mud, and foot area (or effective foot area) relative to weight is not the 'gold standard' by which 'mud competence' is measured. As you demonstrate succinctly in your post.

I reiterate -- the case wherein sinking does not occur is irrelevant to this thread, or my thesis.

this is a case where the elephant to sauropod analogy is weak on the point of 
functional morphology (see below).

Is it as weak as, "they obviously mired because they were just so big"?

:D -- It amuses me that paleontologists who lived and worked in the era of animal propulsion did not seem to consider that "miring" due to size was a problem. It is only scientists who have never worked an animal in ANY environment, or even been in a swamp who insist that it is -- and perhaps wonder briefly how the people who lived in that techno-era could have possibly missed it.

However, the accommodation of compliant substrates is not merely a matter of 
stability.

Actually, that is what the thread is about. Stability, and now morphing into miring. Not relative overall locomotive efficiency.

Propulsive efficiency is also of great importance, and that depends (in part) 
on how much the substrate deforms.

See above.

and some of them would have been prone to miring on account of having very 
heavily loaded foot sections.

If you assume that a heavily loaded foot section leads to miring. I assert that it does not, when accompanied by power and limb length, which tend to increase along w/ loading.

Despite having passing similarities to elephants, the substrate stress per foot 
in most sauropods was many times greater.

Indeed. As is absolute power and limb length.

Elephants actually have relatively broad feet, while sauropods did not.

How does it work out size to size -- any sauropods whose lower limbs are known that approximate elephant mass?

More to the point, we don't see any specific adaptations in sauropods to moving 
on compliant terrain -

Sauropod foot morphs were constrained to maintain terrestrial competence due to reproductive habit -- the point is not whether they were 'mud-adapted', but simply were they functional?

As you point out, they certainly were.

Despite their bipedality, large theropods would be expected to move more 
effectively on compliant substrates and sink into them less.

Until they do, which is the case I am working with.

That trend holds (mechanically speaking) until we move to a substrate that is so compliant 
that all of the animals in question sink in it deeply, regardless of foot area (i.e. 
theropods sink fully, as well).  At that point, the most effective way to move is be able to 
touch harder sediment below, and that means simple height becomes the best determinate of 
propulsive ability - giving an advantage to tall animals like sauropods as long as they can, 
indeed, reach a less compliant medium below the "quick sand", as it were. >

So we are in agreement, at least in the case where a bottom can be reached. Good.

As the sediment becomes even more compliant, it effectively becomes a full 
fluid, at which point propulsion is swimming, and theropods again become more 
efficient, though I doubt they hunted while swimming very often.

Here we diverge strongly. As the hypothetical 'swimming fluid' becomes denser, and we are not talking about water, but mud, then the absolute power available to shear the fluid, and the power to 'drag profile' ratio determine the density at which the legs stop moving.

Higher buoyancy and what I perceive intuitively to be a superior hydrodynamic profile are likely advantages, too.

Advantage sauropod.

I can describe that all in mathematical terms, of course, but I'm not sure 
anyone here wants to read that...

Mike, w/ all due respect, you have assured me that your calculations indicate that "assisted running" is not possible -- empirical evidence contradicts that.

I am about at my limits today, time and quota-wise.

Maybe I can come back tomorrow.