Re: [asa] Quick Q about coprolite densities

> I was reading about the coprolite mining industry in England in the late
> 19th century and was amazed by the sheer volume of coprolites unearthed
> there. Although not all of these nodules where necessarily fossilized
> excreta it still got me thinking about the volume of faeces in the fossil
> record. Does anyone know of any estimate of volume of coprolites versus
> preserved organismal remains or have any general impressions of how
> common fecal material is versus other fossils? One location that came to
> my mind is the Green River formation. It seems to be loaded with fish
> pellets that I imagine might account for many time the mass of the preserved
> fish themselves. The reason I am interested is that it struck me that in the
> YEC model one would predict that coprolites should be less common than
> other fossils (how many time can the animals taken up by the flood poop in
> a few days?) especially considering faeces could have been easily dissolved
> in a flood while the YEC model considers animals to have been well
> preserved.

It depends in part on how broadly you define fecal matter. Many
microfossils have a high enough surface area to weight ratio that they
ought to dissolve before they sink to the bottom, yet they occur as
massive deposits on the sea floor. Packaged into fecal pellets,
there's enough mass to get to the sea floor. Another important gut
sediment source are organisms that feed by grinding up hard material
(such as parrotfish feeding on coral or durophages that simply swallow
the bits of crushed shell with their prey). Thus, much of seafloor
sediment came through a digestive tract before it reached the
seafloor. (One caveat-there are also important filter feeders such as
clams and larvaceans that do some pre-ingestion sorting and packaging
of things they don't eat. That's not fecal-in fact, for bivalves,
they're called pseudofeces-but it raises the same problem because it's
animal-processed). Likewise, several kinds of organisms live by
ingesting sediment and digesting any organic bits. There are
estimates about the extent to which earthworms process soil; the
greater diversity of deposit feeders in the oceans probably means that
any part of the ocean floor where animals can survive gets eaten and
excreted multiple times.

As to being able to clearly identify material as fecal, I'm not sure
of a total volume. Some sedimentary rocks are peloidal, meaning
composed of little pellets. Actual coprolites (which probably often
include gut contents not yet excreted at time of death) can be very
common in some deposits, and it's likely that a lot of phosphate
pebbles started out as coprolites.

Predator coprolites often contain high phosphate levels, which is one
of the best situations for preserving soft tissue and fine details.
Thus, it's not too unusual to find traces of muscle fiber or other
exceptional material in a coprolite. As far as I know, the only
direct evidence that multituberculates had fur comes from a coprolite.
 Both the preservation of fecal material and of soft tissue within
fecal material could be misrepresented as evidence for a young earth;
in reality, experiments show that high phosphate levels can produce
rapid mineralization, and something that formed rapidly could then be
preserved for an indefinite period of time.

It takes a certain personality to focus on such material. A
Paleontological Society short course a few years ago featured a talk
on coprolites. The speaker reported that, although it is generally
impossible to identify the poopetrator, a very large sample from the
upper Cretaceous of western North America that contained bits of
dinosaur was almost certainly T. rexcrement. There's also a paper of
the Irreproducible Results variety purporting to deal with its
evolution- "On the Origin of Feces". The Paleo Society talk was in
better taste.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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