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Re: sauropod feeding dogma*



From: crpntr@ix.netcom.com (Kenneth Carpenter )

 > >1) The living relatives of some of the Mesozoic trees are in that
 >  >size range: consider Pseudotsuga, Sequoia, some Auraucaria spp,
 >  >among others.
 > 
 > These two points are similar to the argument that  "created" giant 
 > lakes in the Morrison Formation so that the sauropods could stand with 
 > only the top of their heads poking out, i.e., creating evidence to 
 > support a preconception.

Nope - the evidence is there in this case, in the form of fossil
pollen and leaves.  Also, note, this was my *least* important
argument.  Point #2 - that the tree heights suggested by the
sauropod structures is more on the order of 30 to 70 ft - was
a far more important point.

 >  In addition, there is a false assumption that 
 > trees of the Jurassic were so closely related to certain trees today 
 > that they did not evolve much. ... 

I agree with this in general.  However if we take this tack we cannot
draw any conclusions *either* *way* in the absence of fossil wood. The
fact that the living relatives have a certain growth form indicates that
the group has the potential for that form. Whether a particular extinct
species had that form or not can only be determined by other evidence.

I have not studied the Morrison plant fossils in enough detail to
say one way or the other for that time and place.

For the Late Cretaceous of North America, west of the inland sea,
I can site substantial evidence that Sequoia and it close relatives
were very similar in general habit to the living members of the
family Taxodiaceae. (Though the fossil Sequoia I know of seem to have
been ecologically closer to Taxodium than the living S. sempervirens).

 > As I wrote, the fossil evidence in the Morrison Formaion does not 
 > support the exsistence of many giant trees.

How about *small* to *medium* trees??

That is the size that really matters.  Even Amphicoelias would have
been hard pressed to reach up 100 ft under any circumstance.  The
highest they can be argues to have been able to reach would be about
half the total length, at best.

 > >Broad muzzles are indicitive of *non-selective* *bulk* feeders.... A
 > >narrow muzzle indicates a selective feeder, some of which are also
 > >grazers today and low browsers...Thus a broad muzzle does not nec
 > >essarily indicate a low feeder, only one that wolfs down its food
 > >without much selection.
 > 
 > Isn't that what I said? You can also check Carpenter, 1982, Canad. J. 
 > Earth Sci. 19, p. 695.

But you seemd to also imply this was evidence against them being
high browsers.  I was trying to point out it is not evidence either
way.

 > More false asumptions: 1, that all ecological niches of the past are 
 > present today (e.g., we don't have 30 ton terrestrial herbivores) or 
 > 2), that all morphological adaptions we see today can correctly set the 
 > limits behavioral interpretations of the past.

They do, however, give us the only basis we have for such interpretation.
Also, the general selective patterns will not have changed greatly.

 > But as veni, vidi, concreti 
 > pointed out:
 > 
 > >err, ostriches etc....um geese are grazers err swans (ok you could 
 > >look at these as upside down high level feeders...)
 > 
 > Thanks.
 > The point is that the giraffe model have been miss used, over used and 
 > abused.

Actually, ostriches are not really a good comparison.

As Dr. Holtz pointed out to me in e-mail, there is one other factor
that correlates with moderately long necks - long-legged ground
feeding forms.  In these the neck is often elongated to compensate
for the long legs.

One possiblity is that the long neck of the ostrich is due to this
factor.  Alternatively it could be a relic of a past specialization
to high browse, as I suggested might be the case for Apatosaurus.
(I prefer the first idea).

Now, if we look lt long-necked ground-feeding forms we see that the
neck is generally about as long as the legs, but vey little longer.
This applies to the ostrich, horse (Dr. Holtz's example), and also
to herons, storks and other long-legged wading birds.

Sauropods are not long-legged by any stretch of the imagination,
and their necks *far* exceed the leg length, especially in the
diplodocids and euhelopodids.  Thus none of these models can be
considered germane at all.  The set of models to consider in estimating
what sorts of selective pressures might cause this sort of neck
elongation is the set of terrestrial species with highly elongate
necks without cursorial or wading specializations.

Note, I do need to make one correction to my original statement,
it needs to be restricted to terrestrial forms - a very different
set of selective regimes apply in aquatic environments, where friction
is a major factor (I suspect that this accounts for Tanystropheus).
 > 
 > >It is certainly possible that the long neck originally evolved for
 > >high feeding (in the prosauropods), and then was co-opted for a
 > >long, low reach later.  But it seems unlikely to me that this
 > >happened in *all* sauropod lineages. (In fact I have concluded
 > >that Apatosaurs may well have fed as you suggest,
 > 
 > Do I detect someone having second thoughts? ;)

No, just recognizing that evolutionary relics do occur, such as the
human appendix.  However, expensive relics, like long necks, tend not
to last long, evolutionarily speaking, after their purpose becomes
redundant.  This is why I cannot accept the ground feeding explanation
for the extremely long-necked forms like Diplodocus and Mamenchisaurus,
as these forms evolved their long necks from forms with shorter ones.

 > I never said all sauropods feed on the ground. Reread my original 
 > message. I clearly stated that I dispute having all sauropods feeding 
 > in trees and pointed out that diplodocids were probably low browse, 
 > i.e., non-selective, feeders.

There you go again, equating non-selective with low-browse.

I find the extreme neck size in most diplodocids to be too great to
be reasonable in a graviportal, non-wading ground feeder.  Only in
Apatosaurus is the neck sufficiently "ordinary" for such a secondary
switch to to be believable. Also, Apatosaurus has a heavier buiild
than is typical for diplodocids, making it likely it had lost the
tendency to rear up.

In short, I am suggesting that the reason that Apatosaurus is such
an *unusual* diplodocid is because it had switched from the normal
high-browse to an atypical low-browse habit.

 > Diplodocids are NOT tall in the front nor do the 
 > vertebrae indicate  the neck was carried erect (sorry, Greg).

Yes, we know that.  Rearing up could compensate for that.
Thus the neck position is not, by itself, sufficient evidence.
It needs to be shown that the reaered feeding position is untenable.
Given the rearward positioning of the center of mass, I think this
may be hard to do.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.