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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
MS Biostratigraphy
Weston, Wyoming
www.wyomingdinosaurs.com

On Dec 21, 2006, at 8:58 PM, don ohmes wrote:



----- Original Message ----
From: Dann Pigdon <dannj@alphalink.com.au>
To: DML <dinosaur@usc.edu>
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 stones; if
the stones were vitrious (like quartz) then they almost certainly weren't
ingested for mineral content. If, on the other hand, the stones contained
significant amounts of carbonate (or any other disolvable minerals) then
there's a chance they were like internal salt licks. Of course, carbonate
minerals probably wouldn't last long enough to end up in the fossil record,
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 better
source of minerals than stones (lots of modern species eat clay for example,
even humans). Perhaps the stones were collected unintentionally along with
sediments? If so, then they were unintentionally swallowed during the act of
intentionally aquiring minerals (therefore sort of semi- intentional). That
said, some of those stones would have been more than noticable on the way
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
purpose.

___________________________________________________________________

Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com
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