Carcharocles angustidens tooth in phosphate nodule, pictured from collections at the Charleston Museum, Charleston, SC (PV 55.105.25).
It starts with an S and it ends with a T,
and it comes out of you and it comes out of me.
I know what you’re thinking if you call it that,
but be scientific and call it scat!
- The Scat Rap (Doug Elliot; Bullfrogs on your Mind)
Have you heard the stink lately? One particular fossil has made near-viral fame on the internet to the tune of "Ancient shark tooth and bite marks found in crocodile poo," and other sensational titles: (Charlotte Observer, Newsweek, Daily Mail, EarthTouch News, IB Times) as thousands of people have discovered the defecatory nature of our Earth's fossil history.
The specimen: a tooth of the giant white shark, Carcharocles angustidens, embedded in a nodule claimed to be a fossilized piece of dung from an Oligocene crocodilian. (Pictured here.)
All of this dirty talk got us here at CFA (located in the town where the specimen was discovered) to wonder about the nature of the recent discovery, and its place on the stinky stage of fossilized poo. Is it truly a coprolite? What are examples of other coprolites found? And how can science help us determine poop from, well... not poop!
A LOOK into the literature
Fossilized feces, or coprolites (from the Greek kopros=dung, lithos=rock) as they're known to paleontologists, are not a new discovery. If anything, these fossils are among some of the oldest collected, with Mary Anning and William Buckland studying the existence of these "bezoar stones," or "fossil fir cones" as they had previously been described. In 1835, Anning and Buckland properly identified the masses as remains that had passed through the intestines of reptiles and fish from the Jurassic Period, over 176 million years ago (Ma), and not fossilized pine cones or masses from the digestive tract, as commonly assumed at the time. [Britannica]
Over time, coprolites became recognized more frequently, and added to the list of trace fossil that can be found in fossiliferous deposits.
More recently, Milan et al. (2012) conducted a study of a crocodilian coprolite with a partially exposed fish vertebra and described feces of crocodiles as alternating layers of dense and less dense material, laid down in the original way it was produced in the intestines of the consumer. The overall shape of crocodilian feces is elongate, cylindrical, and occasionally flattened (in cross section), with concavo-convex units segmenting the entire piece. Coprolites belonging to fish (sharks included, as they are cartilaginous fish) are spiral shaped, and those specifically of sharks are known to be "heteropolar" spirals, meaning the spirals are more compacted on one end.
Upon scanning and analysis of the coprolite with included fish vertebra, Milan et al. concluded that it belonged to a marine turtle or possibly large bony fish or shark, based on one distinguishing feature: the fish vertebra was entire. The digestive tract of crocodilians contains high concentrations of hydrochloric acid, which readily dissolves and decalcifies all bone before secretion; whereas the gastric acid in turtles is not nearly as strong, leaving fish bones and even mollusks intact upon excretion.
[Milan, J., B.W. Rasmussen, N. Lynnerup. 2012.]
In another 2012 paper entitled "Crocodylian scatology - a look into morphology, internal architecture, inter- and intraspecific variation and prey remains in extant crocodylian feces," J. Milan analyzed the remains of extant crocodiles. In the study, published in a bulletin from the New Mexico Museum of Natural History & Science, Milan goes on to describe external features of crocodilian feces such as longitudinal banding and cylindrical tapering, and internal features such as the alternation of dense "clay-like" material and undigested animal remains. Milan event went so far as to screen the scat for all animal remains, but not a trace of bone or scales was detected, even with a mesh size of 0.122 millimeters! (That's about the width of a thick human hair!) [Milan, J. 2012.]
A ROCK by any other name...is still a rock
Paleontologists give rocks that take on the appearance of fossils the name of pseudofossils. "So," you ask yourself: "are there pseudofossils of feces? What if something is shaped like poo, but doesn't fit the bill of a coprolite?" Why, we're glad you asked...
If you're a resident of Lewis or Cowlitz County in western Washington State, you may be familiar with this pseudocoprolite:
"But wait!" You say, "How do we know these are really just rocks? They LOOK exactly like a big pile of poop!"
Wrong! These are concretions composed of limonite and goethite (pronounced GER-tight), iron-rich minerals, and are perhaps some of the most convincing pseudocoprolites out there! The telltale sign that these strange rocks are just that -- rocks -- can be seen if one is broken open to reveal the hollow, layered chambers (inset magnified view, above). Unlike layering in coprolites, the formation of these concretions leaves empty layers of air between mineralized deposits.
By definition, a concretion is "a hard, compact mass of mineral material formed when minerals in water are deposited about a nucleus (such as a leaf or shell or other particle) forming a rounded mass whose composition is usually different from the surrounding rock." [