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Re: Bones and Stomach acid



Joe Gilvary <dinosaur@gilvary.net> wrote:

> How is the freeze-thaw cycle ruled
> out to diagnose this kind of
> mis-identification?


I have only seen examples of weather-induced enamel exfoliation, so I can't be 
much help on the identification of digestive erosion of bones.  From what I've 
seen of exfoliation, the enamel is cleanly removed from the underlying dentine, 
as though one were removing an eggshell from a hard-boiled egg.  Sometimes, 
with careful searching, flakes of the exfoliated enamel will be found laying 
nearby.

Exfoliated teeth usually form after the tooth has been exposed to the modern 
atmosphere.  Therefore, be suspicious of all purported "acid-etched" teeth that 
were discovered laying *on* the surface of the outcrop.

I have a photo of a Daspletosaurus tooth from the Judith River Fm. that was 
half-exposed when found.  The base of the tooth was still encased in the rock 
and the enamel on that part of the tooth was pristine.  The tip of the tooth 
was poking out of the ground and had lost all of its enamel layer.  It gives 
the tooth an unusually narrow, highly-pointed shape. (email me if you want to 
see this photo).

My understanding of *digestive erosion* of bones, in particular teeth, is that 
there is more of an uneven removal of surface bone (pitting, etching, etc.).

One strong piece of evidence that a bone that was etched by ancient processes 
(of which digestive erosion would be only one process) would be to excavate the 
bone from solid rock.

<pb>






On 8/19/2010 6:52 PM, Phillip Bigelow wrote:
> When finding teeth lacking enamel, it is important that exfoliation of the 
> enamel due to freeze-thaw cycles (created while the bone was laying on the 
> surface of the ground), be first ruled out.  Freeze-thaw cycles do an 
> excellent job of removing tooth enamel from the dentine of a fossil, and many 
> an exfoliated tooth has been mis-identified as a tooth that passed through a 
> critter's digestive tract.
>
> <pb>
>
>
> ---------- Original Message ----------
> From: Patty Ralrick<pattyralrick@hotmail.com>
> To: Dinosaur Mailing List<dinosaur@usc.edu>
> Subject: RE: Bones and Stomach acid
> Date: Wed, 18 Aug 2010 09:53:17 -0600
>
>
> Check out this citation for more info. It's a pretty cool paper.
>
> Fisher, D.C. 1981. Crocodilian scatology, microvertebrate concentrations and 
> enamel-less teeth. Paleobiology 7(2):262-275.
>
> Sorry if someone else has already posted this. I get the mailing list as a 
> digest once a day and am sometimes a bit behind the times. : )
>
> Enjoy!
>
> Patty
> ***********************************
> Patty Ralrick
> PhD Student, Biological Sciences
> University of Calgary
> Calgary, AB, Canada                                   
>
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