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Re: Gastric stones of dinosaurs were not for milling food !




----- Original Message ----
From: Martin Baeker <martin.baeker@tu-bs.de>
To: don ohmes <d_ohmes@yahoo.com>
Cc: dinosaur@usc.edu
Sent: Tuesday, January 2, 2007 12:02:12 PM
Subject: Re: Gastric stones of dinosaurs were not for milling food !

Hi again,

just some other comments.


>>how much food would they be able to gather -- 200kg? 

--------------- Relative to maximum acquisition capability *and* daily 
nutritional requirements-- don't know, that was one reason for the original 
post; to my surprise, no one has come up with numbers or references. Surely 
someone has made a jaw-model to constrain possible acquisition of leaf/mass per 
day by large sauros, but so far, I can't find their work. But yes, 200 kg seems 
do-able to me from the very rough estimates I have made.

Do you really think your estimates are precise within less than a
factor of 2 or 3? (i.e., 200kg is possible, but 500-600 is not?)

==== All I was trying to do was set upper bounds using what I feel are very 
generous assumptions. BTW-- M Taylor posted a reference on this... thanks, Mike.

>>Can you really raise the nutritional value in a
>>plant by a factor of 2 or 3 just by increasing N2-content?

------------- Increases in n-value per *free nitrogen* are well-known. An 
increase in ambient free nitrogen due to 
ambient-free-nitrogen-to-atmospheric-N2 proportionality is speculation on my 
part, although it seems eminently logical. No idea what the curve would be. 
What is not so speculative is that lower evaporation rates would allow an 
increase in the CO2 intake per unit H2O lost for a given plant, which in turn 
would allow an intra-plant re-allocation of mass...

I don't know enough about plant physiology to comment on the
plausibility of this assumption. My question is simply this: To get
the factor of 2 or 3 you require, wouldn't this mean that the N2
content was a factror of 2 or 3 higher? 

===== Uh, which assumption? And, I must repeat, I am unaware of quantifying 
anything other than to point out that gathering in more than 600 kg/day would 
be very hard to do w/ sauropod jaws, even with very generous assumptions in 
terms of average leafmass per bite and average bites per minute. Marjanovich's 
comments not withstanding. Again, perhaps someone has a reference on jaw 
dimensions/tooth placement/tooth shape?

With corresponding change in
air pressure, wouldn't this have effects that could be measured
(completely different weather, completely different aerodynamics of
flyers - and we are not talking about the 15% or so that were
discussed a few weeks ago.)

===== Frequency and velocity of air circulation relative to temperature are 
inverse to pressure; as are evaporation rates. Free nitrogen generated by 
lightning seems inevitably proportional to N2 partial pressure, but I know of 
no reference. IMO, the plant record as a whole is a good qualitative fit 
relative to a hypothesis of gradually declining air mass. It is logical that 
relative wing loads would be higher, in fliers optimized to a denser 
environment than present-day. Outliers on the upper side of the Hartman (is 
that the right guy? I forget.) slope, if you will. I don't know the current 
fossil record well enough to comment, but there is good support for that idea 
in extant populations. I do know that insects that have insufficient wing area 
to achieve takeoff at 1 atm can fly if you increase the pressure. Again, you 
seem to be saying I have advanced some number that I am unaware of. Only 
numbers I have mentioned are to set upper OR lower bounds, *not* upper AND 
lower bounds.
 There is a big difference.

>2. Don't forget that there were other rather big critters existing,
>like Baluchitherium (or is it Indricotherium or Paraceratherium - I'm
>not too good with mammals...). These were in about the same mass-range
>as a sauropod (18 tons, I think, is a reasonable estimate), and
>obviously they were also able to gather enough food. So why should
>sauropods have that much bigger problems?

----------- I have been referencing *large*, that is, maximal sauropods. 
Correct me if I am wrong; the skull/jaws/teet
nown-as-Baluchitherium are considerably more robust than the much larger 
Diplodicus, et al?

O.k., take another example - Steller's seacow has been estimated to
need about 700kg of water plants per day - and its head was smaller
than that of a big sauropod. If they can do it, why not the sauropod?

==== I can't see any parallels between wallowing around in a kelp forest and 
harvesting leafs out of treetops. By really weird coincidence, I've done both. 
Quite extensively, as far as trees. BTW, is that wet weight?  Must have been an 
amazing animal, eating kelp plants like giant strands of spaghetti..

So, all-in-all, I think that your assumption is not very parmesaneous ;-)) 

==== Heh. Can I have some pasta w/ that? Just kidding. Your English is 
infinitely better than my Deutsch. 

Cheers,

Martin.




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