Bone Taphonomy (was: Dinosaurs with Guts)

["Jerry D. Harris" <dinogami@hotmail.com>]

Our Local Texan Jon "Jon-Boy" Wagner wrote:

> Note that even finding one specimen articulated within another does not 
> PROVE ingestion (as some point out regarding the infamous "cannibal" 
> ceolophysis... but don't ask me, I've never seen the thing).

  This assertion came from an observation -- I don't know who is supposed 
to have originally made it -- that one can see the ribs from _both_ the left 
and right sides of the adult _Coelophysis_ overlying the supposedly-ingested 
juvenile -- this would imply that the juvenile isn't inside the adult's 
peritoneal cavity, but that the adult is _on top_ the juvenile.

> It is not at all uncommon for different bones in a quarry, often bones from 
> the same animal, and sometimes even two fragments of the SAME BONE to 
> exhibit different weathering styles. Sometimes, this indicates locally 
> differeing chemical "micorenvironments" (either in burial, or exposure), 
> sometimes it indicates that some of the bones sat around longer, or were 
> transported further, prior to burial.

  When the texture within a single bone is largely porous (as was noted, 
meaning with the periosteal layer worn off and the trabecular interior 
exposed) on one part and much less so on another (with the periosteum 
intact), this frequently indicates that the porous part was exposed 
subaerially while the non-porous portion was buried.  In taphonomic terms, 
the weathered part would be in Stage 1 of Fiorillo & Behrensmeyer, while the 
unweathered part would be in Stage 0.  I have a Recent cat skeleton I 
discovered, mostly disarticulated but largely associated, on a field trip 
years ago that demonstrates both of these conditions -- the porous, 
weathered elements were sitting on the surface; the smoother, more intact 
ones I had to scrape away some topsoil to find.  The pelvis is particularly 
interesting -- it was half-buried and half-exposed, pretty much along the 
sagittal symphysis, so one half is rough, flaky, and porous, while the other 
is much nicer bone.  As Jon notes, this isn't the _only_ explanation for 
intra-bone preservational differences (transport distance and selective 
groundwater percolation are two others that are relatively common), but it's 
a noteworthy one.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316
Phone: (215) 573-8373
Fax: (215) 898-0964
E-mail: jdharris@sas.upenn.edu
and     dinogami@hotmail.com
http://www.sas.upenn.edu/~jdharris

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