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.

Index

Amber || Casts & Molds || Compactions || Compressions || Coprolites & Gastroliths

Drying & Dessication || Freezing || Impressions || Molecular Fossils || Permineralization

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