Fossils: Window to the past
Coprolites & Gastroliths
Both coprolites and gastroliths are trace fossils.
These fossil types 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?
Coprolites are the fossilized or preserved remains
of the contents of the intestine and the excrement of organisms: fossilized feces.
Coprolites are quite rare because they
tend to decay rapidly. 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 also very phosphatic in composition.
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?
As fossilized feces, coprplites indicate the former presence of organisms in the area where they
found. They cannot indicate exactly what organisms were present (e.g.,
the specific animal species). However, there are exceptions. Sharks have a distinctive character of
spiral valves in their intestines. Coprolites of sharks show grooves
made by those spiral valves. When the organism shows such distinctive characteristics,
it would be possible to identify the organism via coprolites.
Coprolites also aid in the interpretation of the
diet of the organism. There are also often 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 indicates they mostly
lived among fish and cephalopods.
Coprolites are worth more than their paleontologic value.
There are people out there who treasure them as gifts!
Gastroliths - What are they and
what do they tell us?
Gastroliths are fossilized gizzard stones and 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. They have rounded
edges and smooth polished surfaces, but they can only be called gastroliths
when they are found in presence of reptilian remains as pebbles
are also round and smooth. However, unlike gastroliths, a pebble's appearance
is a result of erosion by running water or wind-blown dust. A gastrolith's
smoothness is 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.