August 3, 2018
Not all rocks that look like poop have a fecal origin. Here are a few things to consider when trying to make this determination:
- Location, Location, Location – If you haven’t guessed, the first and most important thing to consider is the location your rock was found. Don’t expect to find a coprolite unless you find it in geologic area/layer where other fossils are found. If you find things like bones, teeth and fish scales, or prehistoric tracks, you may just be in in luck.
- Shape – While fecal matter can be rather freeform when exposed to the elements or when digestion issues arise, most coprolites are shaped like poo. As with modern extrusions, fossilized feces can be shaped like pellets, spirals, scrolls, logs, piles, etc. Their shape is dependent on shape of their producers intestinal and anal structure. Look for things like compaction folds and pinch marks.
- Texture - Most coprolites are fine grained. If your specimen appears granular under magnification, it is most likely not a coprolite. There are some exceptions, such as marine creatures that feed on bottom sediments or coral. That is why knowing the location and geology of the area where it was discovered is so important.
- Inclusions – Many times, coprolites will have visible inclusions. Things like fish scales, bone fragments, and teeth may not get fully digested, and can be visible on the surface. Some animals ingest stones for ballast or digestive purposes. These are known as gastroliths, and if present, are generally smooth.
- Composition – Because herbivore scat tends to break a part and decompose rapidly, it rarely survives the fossilization process. So most fossil poo that is found is from carnivores. The reason for this is that their poo is usually high in calcium phosphate, the same mineral found in our bones. This mineral can appear in many forms. It can be hard and dense or soft and porous. If the potential coprolite appears soft and porous, there is a quick test that is often used in the field. If you touch to stone to the tip of your tongue and it sticks, chances are, it is high in calcium phosphate and could be a coprolite. If you are not that brave, you can also touch it with wet fingers to see if it feels sticky, but this is not nearly as fun. If the calcium phosphate takes a harder, denser form the “lick test” won’t work. In some instances, chemical analysis is required to definitively identify the mineral composition.