Step aside Megalodon, this fossil is raising quite a stink!

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." [Kansas Geological Society]

 

Trickily enough, some concretions and other geologic features can mimic similar external morphology that an untrained eye would attribute to a coprolite. The following images are of various pseudocoprolites, geologic features, and fossiliferous nodules.

 

Above: Concretion with weathered limonite and goethite visible on the interior. (ChM specimen.)

 

Above: Concretion with weathered limonite and goethite visible on the interior. (ChM specimen.)

 

Above: Concretion with weathered limonite and goethite visible on the interior. (ChM specimen.)

 

Above: Phosphorite with embedded ammonite. Locality - France. (ChM specimen.)

 

Above: Concretion with weathered limonite and goethite. (ChM specimen.)

 

Above: Phosphate nodule with embedded Carcharocles angustidens tooth, exhibiting phosphatic steinkerns (internal casts) of bivalves. Locality - Charleston. (ChM specimen, PV 55.105.25.)

 

Above: Phosphorite. Locality - France. (ChM specimen.)

A CONVERSATION with the experts

 

To uncover more scatological information, CFA headed to the Charleston Museum and the Mace Brown Museum of Natural History to speak with experts there about coprolites, and get the scoop on fossil poop. (Tap or hover over images for captions.)

 

 

Charleston Fossil Adventures, LLC (CFA): Good morning, gentleman. Thank you for agreeing to be a part of this interview today. Before we begin, could you please let our readers know your names, affiliations, and respective positions?

 

Matthew Gibson (MLG): My name is Matthew Gibson. I'm the Curator of Natural History at the Charleston Museum (ChM).

 

Robert Boessenecker (RWB): My name is Robert Boessenecker, PhD, Adjunct Lecturer, Department of Geology and Environmental Geosciences, College of Charleston.

 

 

CFA: How many years of experience in paleontology do you hold?

 

MLG: I have 13 years of experience in paleontology. My undergraduate degree was with Johnathan Geisler at Georgia Southern University. I worked on whale material and similar vertebrates to what we have here in Charleston. (Shark teeth, for example.) My graduate degree is from East Tennessee State University; I have a Master's Degree in Paleontology from there.

 

RWB: Formal experience, 15 years.

 

 

CFA: What is a coprolite?

 

MLG: Well simply, a coprolite is fossilized dung. All of the biotic material has been replaced with minerals present in the layer it was buried in.

 

RWB: A coprolite is fossilized feces. Typically, identification is based upon external morphology -- the shape of the sample. If it's not shaped like poo, it's probably not!

 

 

 

CFA: What do you look for in a specimen to determine it is a coprolite?

 

MLG: I would look for the shape. So, basically, if you've seen a carnivore dung sample, they're elongate -- almost torpedo-shaped. You usually see striations along the sides. Where it breaks, you may find bones or other materials to show it was from a carnivore. (Herbivore coprolites are a little trickier.) Carnivore coprolites are pretty much what you'd expect to see if you went out and collected dog poo...it pretty much looks like that, except it's fossilized!

 

RWB: It's difficult to identify coprolites because they can come in many shapes. They are usually cut open and examined under a microscope. Without [that], it's usually difficult to identify a coprolite. The biggest thing is to look at the shape; everybody knows what their own looks like... Most coprolites are going to have some sort of fusiform shape. That's not always true, because sometimes you'll have critters like rabbits, wombats, and most herbivorous mammals where it breaks apart in clumps. But most carnivore [feces] -- which make up the majority of the coprolite record -- have a fusiform shape. In other words, it will be tapered at both ends; sometimes they'll be blunt, sometimes they can be long and 'rope-like' or cylindrical, but generally, it has to be passed through a small hole so there's going to be some sort of fusiform, teardrop, or cylindrical shape.

 

 

CFA: What species are represented by coprolites in the South Carolina Lowcountry?

 

MLG: I know we have crocodilian coprolites, there have been some tales of shark coprolites. I have not come across any in our collections; all specimens we have are crocodilian or thought to be crocodilian. There may be some turtle mixed in, too. I will admit, many of our coprolite samples are 'TBD' (To Be Determined) -- we know they are coprolites, but we're not certain what animal left them.

 

RWB: Identifying the producer of a coprolite is very, very difficult. Coprolites are trace fossils, and people who study trace fossils always stress the difficulty of linking a trace fossil with a producer in the fossil record. This usually requires matching the anatomy. That's easier for footprints where you have the skeleton of a foot and you can match it to the size [of the track]. If they're [1] the same age (from the same rock unit) then that's a reasonable hypothesis to be made. The most slam dunk examples are [2] trilobites that are found on a [rock] plate, where the tracks lead up to the dead animal, itself. So, you literally are looking at the fossilized final steps of that individual. Coprolites satisfy neither of those [requirements]; they are usually found in isolation from the trace maker, and we have no idea what the rectal anatomy of most fossil species is like.

 

 

CFA: Is it reasonable to compare the rectal anatomy of modern species within the same group and try to extrapolate that to the fossil species?

 

RWB: Yes, that's called extant phylogenic bracket. That's basically using modern species to make inferences about close relatives in the past. Generally speaking, if we see something in the rock record that looks like 'crocodile turd,' it's likely to be one. Or, something that at least had colorectal anatomy similar to a crocodile, and there's many candidates that may have approximated that. But we don't know, since we don't have the soft tissue preservation (we likely never will). 

 

 

CFA: Have coprolites been found with vertebrate remains still present?

 

MLG: In our collections we have very few samples with vertebrate material in [the coprolite], but what we do have is a little bit of fish material: small fish vertebrae, though fairly broken apart.

 

RWB: Yes, in rare cases shark teeth have been found. I believe there are a few examples of coprolites found with crocodilian teeth inside, and the teeth have lost most of their enamel, owing to stomach acid. There are some cases, but it depends upon the group in question. [Shark vs. croc vs. fish...] Coprolite specialists would call whatever is found within a coprolite an inclusion, and the short answer is yes. Fragments of prey items whether it's plankton or shells or bone fragments or teeth or bits of wood, inclusions like that are widely known. But, you can often have coprolites with inclusions that you can't identify to a particular species or genus.

 

 

CFA: Have coprolites been found with invertebrate remains still present?

 

MLG: I'm not aware of any in our collections. I could see some invertebrate remains -- very fragmented shells, things like that -- [being possible]. Invertebrate remains are pretty susceptible to acidic solution, so it would be very difficult to preserve those.

 

RWB: Yes. The short answer is it's typical in species that eat invertebrates. There have been studies of shell ducks in Europe which poop out 'shell hash' and that could in theory fossilize. I've always kept my eyes peeled for little pellet-like pods of small finely-milled shell fragments (which could in theory be some kind of bird like those I mentioned) or some kind of durophagous -- shell eating -- fish. There are plenty of examples of [durophagy]. Parrotfish, for example. I've not found one yet. I've been aware of coprolites and what to spot for 15 years, and on the west coast (i.e. California) I've only found two to three convincing, plausible examples. I'm not saying they are, I'm saying they might be. Everything else I've seen would not fit the bill.

 

 

CFA: Based on the photos circulating the internet, what is your professional opinion on the purported coprolite found here in Charleston?

 

MLG: Based on phosphate samples I've seen collected in the area, it looks like a phosphate nodule with a shark tooth in it. We have a couple phosphate nodules in our collections that also have a shark tooth in them. They're not embedded to the level that this tooth is, but honestly, it's just the way the phosphate forms around the tooth: for some [nodules] the tooth is right underneath, others, the tooth is hanging off the side... It really just depends on how the tooth contacted the phosphate as the nodule formed. I don't think it's out of the realm of possibility that this is just a phosphate nodule that formed around a shark tooth.

 

RWB: I have many thoughts on that piece: 1) Nobody knows what the purported coprolite is made out of because it hasn't been sampled, and nobody's looked at it under a microscope. That necessitates some degree of destructive sampling, and I know it's in a private collection and I'm assuming a lot of money was paid for it, so nobody is interested in cutting it up with a rock saw and making a microscope slide out of it. 2) Second, and most importantly, it doesn't look like a coprolite. It's rock-shaped and irregular, it has an irregular surface texture, and most coprolites are kind of smooth. I've never seen modern dung that has that surface texture. Some of the pits in it could be from 'boring bivalves' like piddock clams. There are cases of coprolites that are already lithified and subsequently have piddock clams bore into them. Piddock clams require a hard substrate, and coprolites in a phosphatic bone bed, along with phosphate nodules and occasionally early mineralized bone -- all of those are hard substrates that piddock clams can bore into. I'm not necessarily convinced all of those pits [on the specimen] are boring clams, as some of the holes don't have smooth walls with a sharp, circular opening. Some of them look like the naturally-occurring pits that appear in phosphate nodules. The specimen altogether looks like a phosphate nodule. It looks like a small concretion. Phosphate nodules are also made of calcium phosphate, just like coprolites. They can often have shark teeth embedded in them. In the Charleston area, they can also have molds of solitary corals. Our species of coral is called Balanophyllia and it gets up to 1.5 cm wide to about 1 cm tall, and calcium carbonate (the mineral that makes up shells and limestone) dissolves during periods of time when phosphogenesis is occurring. So if you make phosphate nodules, you end up dissolving a fair bit of calcium carbonate, and any shell material inside that phosphate nodule gets dissolved out, so you end up with cavities inside. 3) The shape, the pits, the size, all of these look like the hundred of thousands of phosphate nodules you see lining the shorelines of our local rivers in Charleston. 

 

 

CFA: Is it credible that a shark would a) bite a pile of dung from a crocodile, and b) if so, could a tooth dislodge in the excrement?

 

MLG: That seems incredibly odd for that to happen. I have been to talks where people have suggested some coprophagy among sharks. ..... [Describing the scenario leading to the purported specimen.] What you have here is a croc that's near the surface [of the water], with a shark below. The croc uses the bathroom, the coprolite drops, and for some reason the shark wants to investigate it. ..... I suppose, in the realm of possibility, yes, possible. Why the tooth would break off? It would have had to be hanging on by a thread. (It's not like dung is hard.) So the fact that the shark took an investigative bite -- which is usually light -- to lightly tap this dung to break off its tooth but not split the dung in half? I don't even understand how that would happen.

 

RWB: First, sharks do test bite, and they will bite inanimate objects. There is a pretty solid example of a true shark-bitten coprolite from the Miocene of Maryland in the Calvert Formation. In that case, the authors of the study took latex and poured it into the shark bite and pulled it out. Sure enough, the tooth marks look exactly like a tiger shark tooth. In that published case, I believe it. There are also some pretty good examples of coprolites bitten by gar fish -- which have large needle-like teeth and tiny needle-like teeth, so you'll see this pattern of large and tiny tooth marks coming at opposite directions, and that