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Re: Gastric stones of dinosaurs were not for milling food !
DeLurking for a few anecdotal observation. I live in Hell Creek
Cretaceous sandstone country. The closest source of quartzite is
many dozens miles away and all down hill from here recently and way
too far down the paleo-slope during the Cretaceous for deposition in
these rocks. I routinely run upon quartzite gastroliths while bone
picking up here in the Hell Creek always in affiliation with fossil
sites. I have observed that quartzite gastroliths are selectively
identifiable (easy to see and ID) as such in contrast to lime based
stones which are harder to spot against the background sediments and
selectively are weathered away anyway. (Probably dissolved partially
away in the Hell Creek ground water chemistry, gut chemistry or by
todays acid precip.) There is obviously a preservational bias in
operation as well as a bias against accurate identification of non-
quartzitic stones. That being said, at associated fossil sites where
the quarts varieties are common, I do also observe limy sandy rounded
cobbles (which may have been gastroliths). I am not sure how one
would be sure. They have none of the obvious features (such as a
semi-gloss surface, no percussion marks, and a redish stained
surface) that quartz gastroliths have. I suspect there wasn't too
much bias by the original animal. I would think that sites such as
salt licks and other easy to munch minerals would be the preferred
method to get your vitamins. Many critters swallowed them from the
crocs to the big dinos and probably everything down to and including
chicken sized avian theropods. The average gastrolith I find is the
size of a large Idaho spud though I routinely pull what appear to be
really little (2 mm) ones out of Harvester ant hills. I have one
that is 7 inches long and 3 inches across that was found in
affiliation with a mixed bone site. It weighs at least 5 pounds.
They would make good ballast for those crocs.
One may speculate that as a crop becomes less populated by stones
(because of digestion of limy ones) they animal would fill up on new
ones eventually thinning out the diversity of the mix. The tendency
would be to accumulate quartz stones at nearly 100 percent ratio
eventually. Replacement of them would only occur with passing or
wearing down which would take a long time indeed.
On an historic note, the previous owners of our ranch used to dig up
Hell Creek oyster beds and feed the broken shells to the chickens
here for mineral and gizzard stones. It took me a while to locate
the remnants of the beds because they were mostly excavated 60 years
ago and this is a big place.
Frank (Rooster) Bliss
On Dec 21, 2006, at 8:58 PM, don ohmes wrote:
----- Original Message ----
From: Dann Pigdon <email@example.com>
To: DML <firstname.lastname@example.org>
Sent: Thursday, December 21, 2006 10:37:01 PM
Subject: Re: Gastric stones of dinosaurs were not for milling food !
Richard W. Travsky writes:
On Thu, 21 Dec 2006, Dora Smith wrote:
I missed just one detail.
If the stones were not for milling food, what were they for?
One article suggested it was for the mineral content, my thought is
ingestion was incidental ;)
There's one easy way to tell dietry from non-dietry ingestion of
the stones were vitrious (like quartz) then they almost certainly
ingested for mineral content. If, on the other hand, the stones
significant amounts of carbonate (or any other disolvable minerals)
there's a chance they were like internal salt licks. Of course,
minerals probably wouldn't last long enough to end up in the fossil
unless death was soon after ingestion.
-------- If the stones were dissolve-able, would that throw a
monkey wrench into the 'stone to body mass ratio' argument?
Personally, I'd have thought that loose sediment would have been a
source of minerals than stones (lots of modern species eat clay for
even humans). Perhaps the stones were collected unintentionally
sediments? If so, then they were unintentionally swallowed during
the act of
intentionally aquiring minerals (therefore sort of semi-
said, some of those stones would have been more than noticable on
down. It's hard to imagine a sauropod swallowing a fist-sized stone by
accident - unless they provided both mineral content AND a mechanical
digestive advantage. Crocs certainly use gastroliths for more than one
GIS / Archaeologist http://www.geocities.com/dannsdinosaurs
Melbourne, Australia http://heretichides.soffiles.com