Window to the past
Coprolites & Gastroliths
Coprolites and gastroliths belong to the category of trace fossils.
Both these types of fossilization deal with the behavior of the organism
from which they came rather than the actual organism itself.
Coprolites - What are they and
how are they formed ?
By formal definition, coprolites are the fossilization or preservation
of the contents of the intestine and the excrement of organisms, or quite
simply they are fossilized feces. Coprolites are quite rare because they
tend to decay rapidly, but when they are found, they are most commonly
found among sea organisms. Coprolites of fish and reptiles are especially
common. Typically nodular or contorted in appearance, coprolites are composed
of pulverized indigestible remnants of the organism's food, such as portions
of scales, bones, teeth or shells, hence, they are very phosphatic in composition
as well. These pulverized remains of food, otherwise known as "dung-stone,"
are preserved by process of petrification or cast and mold.
What do coprolites tell us?
First, because they are fossilized feces, coprolites on the most basic
level indicate the former presence of organisms in the area where they
found, but they cannot tell exactly what organisms were present (e.g.,
the specific animal species.) However, as in most things, there are exceptions,
such as in the case of the shark. Sharks have a distinctive character of
spiral valves in their intestines, so that coprolites of sharks show grooves
made by those spiral valves. When the organism shows such distinctive characters,
it would be possible to identify the organism with coprolites, but on the
whole it is quite difficult to link feces with a certain organism.
Coprolites are however quite important for the interpretation of the
diet of the organism, as well as being a good indicator of the ecosystem
around that organism. By examining the coprolites and their contents, one
can tell where the organism lived, such as in the case of the Ichthyosaurs,
extinct, aquatic fish-like reptiles. In one instance, coprolites containing
the internal skeletons of two hundred belemnites ("a conical fossil
shell of an extinct cephalopod") as well as fish scales and bones
were found in the Ichthyosaur---this is an indication that they mostly
lived among fish and cephalopods.
Incidentally, coprolites are worth more than their paleontologic value.
Apparently, there are people out there who treasure them as gifts.
Gastroliths - What are they and
what do they tell us?
Gastroliths are in a nutshell gizzard stones. They are usually only
applicable in the fossil study of reptiles. These stones which are found
in the gizzard of the organism help to grind food to pieces as the stomach
muscle (gizzard) squeezes to and fro. Appearance-wise, they have rounded
edges and smooth polished surfaces, but they can only be called gastroliths
when they are found in presence of reptilian remains. It is their association
with reptilian remains that identifies them as gastroliths, because pebbles
are also round and smooth. Unlike gastroliths, however, pebbles' appearance
are a result of erosion by running water or wind-blown dust; whereas gastroliths'
appearance are a result of the chafing between various gizzard stones.
Another indication of the authenticity of gastroliths (i.e., actual gastroliths
rather than pebbles) is if they are found among fossils bones where the
stomach once was. Gastroliths help identify feeding habits and areas where
ancient reptiles lived, as mainly ancient reptiles shared this habit of
grinding food with gizzard stones.
Amber || Casts & Molds
|| Compactions || Compressions
|| Coprolites & Gastroliths
Drying & Dessication || Freezing
|| Impressions || Molecular
Fossils || Permineralization
Reference || Trace
Fossils || Wax & Asphalt
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