In Which Poo(h) is Entirely Surrounded by Water*

A marine coprolite (reptile or fish) from Paleocene? rocks at Big Muddy Lake, Saskatchewan (The Manitoba Museum, specimenV-2388)

The subject of this piece is, literally, old crap, as a change from the metaphorical version that some people might think occupies this page at other times.

A few weeks back, I saw a specimen labelled as a coprolite, a fossilized piece of dung. It wasn’t stated what the coprolite had been extruded by, but the implication was that it was from the back end of a dinosaur (and was therefore, perhaps, exciting). Even from a quick glance it was clear that this was unlikely, as this dropping had obviously been deposited in water, not on land.

Fossil feces, when you think about it, can carry a variety of signatures. They can tell us about the diet of the animal, either from visible enclosed material such as bone bits, or from chemical signatures preserved in the dung. They can tell us about the intestines of the producer, if these have a distinctive form (for example, shark excrement has characteristic spiral markings produced by ridges in the creatures’ intestines). And finally, coprolites can tell us a lot about their environment of deposition.

This possible fish coprolite from Cretaceous rocks at Chain Lakes, Manitoba, is filled with fish scales and spines (MM V-2453).

Most obviously, the simple presence of ancient manure indicates that conditions permitted organic matter to lie around until it was buried and preserved. Normally, of course, dung disintegrates and decomposes; otherwise, we would be up to our necks in it pretty quickly. So its presence suggests perhaps that conditions were too dry for rotting to take place, that burial was so rapid that there was not sufficient time for decomposition, or that special local conditions prevented the growth of microbes.

The shape of the coprolite can tell us whether the turd had been moved at all in the environment, and of course it will demonstrate the effects of gravity. Which brings us back to the well-formed poop I mentioned at the top of this piece. That stool showed little effect of gravitational pull, having the three-dimensional “piped icing” shape that only seems to be associated with dung deposited under water.

A large coprolite from the Upper Jurassic Morrison Formation of Utah, thought to have been produced by a theropod dinosaur (MM V-3106).

Dinosaur coprolites can be difficult to identify, but those that are recognized  seem to most often take on a couple of basic forms, both of which show evidence of pervasive gravitation. Some examples, attributed to meat-eating theropods, look rather like immense dog turds, with clear forms and often containing abundant bone fragments. Coprolites thought to come from plant-eating sauropods are also huge and look somewhat similar to gargantuan cowpats, evidence of their originally high fluid content (bleah).

This coprolite (external view and polished section) is part of a mass thought to have been produced by a sauropod (MM V-3105).

Dinosaur fossils in western North America are often found in river floodplain deposits, but water was where their dead bodies ended up, not where they lived. And where they lived was generally where they excreted.

* If you can’t quite place the title reference, please look at this link.

© Graham Young, 2012