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Re: Gastric stones of dinosaurs were not for milling food !
Various clarifications interspersed below.
----- Original Message ----
From: Martin Baeker <martin.baeker@tu-bs.de>
To: David Marjanovic <david.marjanovic@gmx.at>
Cc: DML <dinosaur@usc.edu>
Sent: Monday, January 1, 2007 5:45:20 AM
Subject: Re: Gastric stones of dinosaurs were not for milling food !
Hi all,
I'm a little bit confused by this discussion, for two reasons.
1. IIRC, this came about by the sugestion that plants had more
nutritional value per mass in the past because of higher N2 values.
----------- Well, I would say speculation rather than suggestion, but yes. To
re-state the speculation; relative to present-day N2 mass (5.14 x1 0^21gm,
IIRC), more N2 mass in the paleo-atmosphere would lead to an increase in free
nitrogen, which would lead to an increased mass-specific nutritional value of
plant matter. Further, the speculation was that there would be more leaf area
per plant (due to lowered evaporation rates), and more biomass per hectare (due
to increased free nitrogen).
*But*, if the amount of food to be taken in by a sauropod is used as
argument, how much larger would the nutritional value have to be to
make this work? If you (Don) claim that it was impossible for
sauropods to get the required amount of food,
---------- Absolutely don't claim it was *impossible* for sauropods to
get the "required" amount of food; I do think the upper limit on the
amount of food large sauropods could gather in a day was constrained by their
jaws and
teeth, and I am interested in getting some empirical data on what that
limit was. It is fair to say I am skeptical of what I consider to be
overly-optimistic assumptions re possible kg/day leafmass "gathered" by those
itty-bitty sauro-heads. I feel quite certain that a 100 kg man armed w/ nail
clippers will gather less leafmass/time than a 50 kg boy w/ a bushhook }:D...
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.
And how much higher would N2-content have
to be to achieve this?
-------------- Don't know.
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...
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/teeth (and possible proboscis) of the
beast-formerly-known-as-Baluchitherium are considerably more robust than the
much larger Diplodicus, et al?
To make things more quantitative, does anyone know (from personal
observation or literature) how long an elephant chews each bite? Cause
if we subtract this time from the feeding time, we could find out how
much a non-chewing elephant might eat per day.
--------- I think this might be apples/oranges re sauropods, but the thing
seems workable.
--------- To sum-- biomass/hectare, ratio of leaf to total biomass, and nutriti
roportional to N2 atmospheric mass. Therefore, increased paleo-N2 at-mass would
have significant, possibly synergistic implications to the (evolutionary)
ecology of maximal sauropods (and just about everything else, but that is
another post).
-------- And Happy New Year to you, as well.
--------- Don
Happy new year,
Martin.
> > Heh. _Average_ 4 bites per minute. For 10 hours. No chewing time figured
> > in. Chewing takes a _long_ time.
>
> > [BTW-- cows don't really chew
>
> They do -- just later.
>
> > Open mouth-- 1 sec. Inhale leaf cluster-- 1 sec. Close mouth-- 1 sec. Pull
> > head back to "strip'-- 1 sec. Swallow-- 1 sec. That is 12 bites per minute
>
> As I said: much more than 4 bites per minute.
>
> > and doesn't not include time spent moving to a new stand, locating the next
> > mouthful, or pre-positioning of head. I think to meet these numbers, even
> > temporarily, is extraordinarily difficult in realistic scenarios re
> > abundance and quality of vegetation.
>
> At average sauropod size you're way beyond the point where, according to Marx,
> quantity changes into quality and... ;-) Seriously: the bigger an animal and
> the longer its gut, the worse the quality of food it can afford to live off.
> If cows can afford to live off grass, surely sauropods can afford living off
> conifer needles? Let alone fern or cycad fronds.
>
> > Do you really think they can average 8 bites per minute over the course of a
> > day?
>
> Of course. I repeat: with these mouthparts they didn't chew.
Priv.-Doz. Dr. Martin Bäker
Institut für Werkstoffe
Langer Kamp 8
38106 Braunschweig
Germany
Tel.: 00-49-531-391-3073
Fax 00-49-531-391-3058
e-mail <martin.baeker@tu-bs.de>