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RE: Gastroliths



Chad,

I'm afraid you've been given some incorrect information. Although I don't
know how many sauropods have been found with gastroliths in the abdominal
area, I believe it is somewhat more than two.  Asking to find them INSIDE
the body cavity is a bit rigorous, though, since the body cavity has long
since been destroyed.  Similarly, we don't have to have a foreleg still
articulated at the end of an upper leg to know it is a foreleg; things get
scattered after death and before final burial, after which they may become
quite compressed.

The claystones of the Morrison are not really aquatic deposits.  They may
have been deposited on river flood plains, but the setting was terrestrial.
In addition, many of them are paleosols, reflecting pedogenic processes more
than original depositional conditions.  The limy deposits I am familiar with
formed on shallow lake beds, and they were often hypersaline, complete with
algal stromatolites.  These were like, perhaps, the Caspian Sea (Asia) and
Lake Chad in modern Africa.  They dried up often, and there were vast mud
flats that the sauropods could walk across.  I have never seen gastroliths
in the limy deposits, which is not to say they never have been--that's just
my experience.  In any case, the Morrison environment in which sauropods
lived was not likely one they could swim in.  Gravel-sized gastroliths could
be found in claystone if the deposit is colluvial (i.e., a mass movement
deposit), and I suspect that some of the Morrison sediments are, being
mixtures of sediment originally deposited in different environmental
settings.

I believe it is true, however, that when a collection of gizzard stones
becomes well rounded from abrasion in an animal's stomach, they may be
regurgitated, whereupon the animal acquires new ones that are rougher and
therefore more effective in grinding vegetation.  I would expect to find
several regurgitated ones in a "pile" or otherwise in a restricted area,
rather than one all by itself.  Don't be too rigorous in your demands for
evidence in this matter.  We have only a few dinosaurs in which ANYTHING has
been found in the area of their body cavities, but that does not mean they
didn't eat; most sauropod finds lack skulls, but they surely had heads.
Maybe look at it this way--we have indeed found two (or more) sauropods with
gastroliths where their body cavity was, so that pretty well proves that at
least some used gizzard stones.  This, in turn, suggests a plausible origin
for polished pebbles in fine-grained deposits of the Morrison.  If we found
roughed-edged pebbles in the same deposits, I would be skeptical also, but
to my knowledge we haven't.

I couldn't quite tell from your posting, and I don't know your background,
but it makes me wonder.  If you are inclined to think that those stones were
deposited by Noah's Flood, you've been hoodwinked by uncritical and
unscrupulous people.  I would be glad if I'm wrong about your motivation,
and you have my apologies if I am. 

What is "TIA"?



> -----Original Message-----
> From: C. Laibly [SMTP:laibly@blue.weeg.uiowa.edu]
> Sent: Monday, April 05, 1999 7:03 PM
> To:   dinosaurs
> Subject:      Gastroliths
> 
> 
>       Can anyone tell me what the accepted theory is about sauropods and
> their possible use of stones to digest? Today in Evolution of the
> Vertebrates, we learned in lecture that many of these stones are found in
> the Morrison Fm in clay or limey deposits. There was some controversy on
> how they could come to rest in a low turbulence depositional environment.
> The one theory mentioned was vomiting from the sauropods as they swam. Is 
> this for real?
>       I really can't see a group of sauropods swimming along and
> vomiting all day! Somebody, please tell me a more plausible explanation
> for the stones. Oh, also mentioned was the fact that only 2 sauropods to
> date had been found with stones inside their body cavities as they were
> discovered. TIA!
> Chad Laibly
> University of Iowa
> Geology/Museum Studies