It's a Dirty Job, But Someone's Gotta Do It
Fossilized feces reveal significant details about ancient life
How often do you laugh when you talk to a scientist? Over the years, I have interviewed and talked with dozens of geologists, biologists and archaeologists. I often come away feeling the researcher’s passion and excitement about his or her subject, but rarely do I come away with a sense of mirth, until I started to talk to people who work with coprolites. I don’t mean to imply that the researchers aren’t serious about their work — they are. But they also exude a healthy sense of humor.
Those who study coprolites — fossilized feces — are a special lot. They get names like Doyenne of Doo-Doo, Professor Poop or Doctor of Dung. They give talks loaded with puns and double-entendres. They make people squirm with embarrassment. They don’t get taken seriously by their colleagues. And yet, when they publish their research, people take notice. “Historically, paleontologists looked at bones and skulls to reconstruct the organism. Now we are looking at the organism’s paleoecology, and coprolites add biological information not available from any other source,” says Karen Chin, curator of paleontology at the University of Colorado Museum in Boulder.
Chin’s most recent work has focused on 77-million-year-old coprolites from the Two Medicine Formation in Wyoming. Based on the coprolites’ size — about equal to the size and shape of a basketball — and nearby bones and eggshells, Chin determined that the fossils were produced by a Maiasaura, a nine-meter-long, three-ton herbivorous dinosaur that walked upright on its hind legs. Herbivore coprolites are unusual because they do not preserve as readily as carnivore coprolites, but the Maiasaura feces are even more unusual in that they show that the dinosaur ate wood — something no paleontologist had ever suspected. “The coprolites really gave us a different perspective and reminded us that we don’t have a modern analogue for these dinosaurs,” Chin says. “Information from coprolites doesn’t answer the entire question [about diet and physiology] but it does provide another piece of evidence.”
A suspect history
Rev. William Buckland coined the term “coprolite,” meaning “dung-stone,” in 1829. He had been studying fossils near Lyme Regis in the United Kingdom, about 200 kilometers southwest of London on the Dorset Coast. Shaped like “oblong pebbles or kidney-potatoes,” the fossils had long been known as Bezoar stones, for their resemblance to concretions found in goat intestines. Buckland, however, had previously described the fecal fossils of hyenas and recognized the similarities between the ash gray-colored Lyme Regis fossils and the white hyena deposits he found in 1822. After concluding he had fossilized feces, and after considering the nearby fossils, he decided that an ichthyosaur had generated the coprolites.
Following his 1822 discovery, Buckland became something of a coprolite fanatic. To prove that his hyena fossils were feces, he collected spotted hyena poop and sent it to be chemically analyzed, which resulted in a note from the analyst: “It may [be] well for you and me not to have the reputation of too frequently and too minutely examining faecal products.” Later, Buckland injected cement into the intestines of fish to record the shape. He also had a much admired table made of coprolites. Buckland later wrote of the ichthyosaur coprolites that “all these vast intervals [of time] seem annihilated … and we are almost brought into as immediate contact with events of immeasurably distant periods as with the affairs of yesterday.”
Buckland’s studies spread across the Atlantic to another man of religion, Congregationalist minister Edward Hitchcock. Hitchcock was also a professor at Amherst College in Massachusetts and a collector of animal tracks. At one of his track sites, he found “a few ovoid flattened bodies … considerably softer than the surrounding rock,” which he suspected were bird coprolites. (Hitchcock never accepted that dinosaurs, not birds, made the thousands of tracks he collected.) He sent the coprolites to a chemist who verified their fecal origin. The confirmation so pleased Hitchcock that in 1844 he wrote, “Truly this may be called a scientific miracle — a resurrection from the dead, and among the many analogous miracles wrought in the nineteenth century I know of scarcely any more marvelous than this!”
Coprolites may have titillated geologists on both sides of the ocean, but to others the nodules of excrement meant money. Starting in the 1840s, miners harvested vast coprolite deposits around Cambridge, England. All of the coprolites were ground to bits, to obtain phosphate, and used for fertilizer.
The industry employed thousands of people and ultimately mined as much as 2 million tons by 1909, some of which was shipped from Ipswich, still home to a Coprolite Street.
Is it scat?
High calcium phosphate content is one of several criteria for determining whether one has found a coprolite, Chin says. Phosphate helps mineralize the feces and most of it originates in the bones of animals eaten by the defecator. “You’d think that poop would squish, but under the right conditions, hardening can occur in less than two weeks,” she says. Herbivore coprolites are rarer because preservation requires an outside source of phosphate, such as marine sediments. They also contain more edible materials for scavengers, such as dung beetles, which left tunnels in the Maiasaura poop that Chin found.
Another telltale sign is shape. It is easier to identify smaller animals by their feces than larger animals. For example, Chin says, primitive fish such as sharks and lungfish produce characteristic spiral deposits, which can preserve beautifully as spiral coprolites. Feces from larger animals tend not to hold their shape. For example, despite Chin’s observations, most dinosaur excrement may simply have splatted when it landed, particularly if the output source was high above ground. Clearly most feces don’t get fossilized; considering how much animals defecate in a lifetime, if more did fossilize, the world might be overrun with coprolites. Beyond splatting issues, other dung destroyers are weather, trampling and creatures eating the feces — called coprophagy.
However, shape can also be misleading. Since the 1920s, amateur and professional fossil hunters have traveled to a small creek in southwestern Washington to collect masses that look so much like real scat that they are often used in practical jokes. But these deposits are problematic. There are too many sizes. They lack calcium phosphate. No other fossil material has been found nearby. All these clues suggest that the masses are not scat. The great ichnologist Adolf Seilacher of Yale University and Germany’s University of Tübingen suggests that they were intestinal casts. Others favor an “Earth farts” theory: moist ash squeezing through knot holes in hollow logs or mud upwelling into voids produced by methane gas movement results in faux coprolites. George Mustoe, a geologist at Western Washington University in Bellingham, who has studied the “coprolites” extensively, says that they are sinuous-shaped siderite (an iron-carbonate mineral) deposits. How they were produced is another question, he says: “They must be produced by an anomalous process without a modern analogue. We are fundamentally missing something.”
“Who dung it?”
Central to Mustoe’s concerns about an animal origin is a lack of any internal clues such as pollen, fish scales, seeds, bones or plant fibers. Without this evidence, one has little more than a pile of scat-shaped rocks. They provide limited ecological, anthropological or geological information as to “who dung it,” as Chin likes to say.
Internal inclusions are what most excite coprolite researchers. They take fossilized dung out of the sphere of “Ooh, that’s gross” or “Isn’t that interesting, so what” to a critical tool that helps scientists understand past lives. “A coprolite is about as personal as you can get,” says Glenna Dean, state archaeologist of New Mexico and coprolite researcher once called the Empress of Excrement. “You find out things people would never admit, things you wouldn’t expect they ate, or things they might not know they ate, such as long strands of hair.”
Dean’s primary coprolite research has been at Hinds Cave, about 280 kilometers east of San Antonio, Texas. The dry climate along the Pecos River preserved thousands of human coprolites deposited over thousands of years of occupation. She found that Hinds Cave inhabitants had a broad diet including cactus, muskrat, wild onions, persimmon and at least one beetle. In the “latrine,” Dean also discovered a fiber sandal in perfect shape; the only problem with it was the poop on the bottom of it. Apparently, Texas’ earliest inhabitants didn’t like to step in dung any more than we do.
When Dean conducted her studies in the 1970s, pollen analysis was her primary stool tool. The techniques were so new that she and several volunteers spent months studying their own feces to see how long pollen remained in their systems. They defecated in caves and kept detailed accounts of what they ate. They covered their excrement with screens to see how long it took to harden to the point that bugs couldn’t carry it away and brought it back to the lab and dissected it. They found that big, heavy grains shot through quickly, but foods with light pollen such as broccoli remained in the researchers’ systems for months.
Pollen not only shows what people ate but when and how they ate. For example, Dean found pollen from onions, a plant that only blooms once a year, early in spring. By looking at whether grass pollen had been damaged or not, she could tell if the grass had been ground up or if it had been consumed whole. In addition, because most of the plants that grew when people defecated 7,500 to 7,000 radiocarbon years ago still grow around Hinds Cave, Dean concluded that people who visited the cave ate what was nearby and did not carry food with them. “The coprolites allow us to put together a story,” she says.
Over the past few decades, coprolite research has moved far beyond pollen research, although it is still important. In April 2008, University of Oregon archaeologist Dennis Jenkins and a team of international researchers reported that 14 desiccated coprolite samples from Paisley Caves in south-central Oregon were radiocarbon dated to 14,000 years old. Predating the arrival of the well-known Clovis people (once thought to be the first Americans) by roughly 1,000 years, the new date is the oldest evidence for humans in North America.
Because of their importance, the Paisley poops may be the best analyzed coprolites in the world. In Denmark, Sweden and Germany, researchers analyzed the Paisley coprolites and found human DNA diagnostic of Native Americans. A lab in California used crossover immunoelectrophoresis — a favorite crime scene technique to identify stains of unknown origin — to corroborate the DNA evidence. And team members in Florida and Oxford radiocarbon dated the coprolites with accelerator mass spectrometry, which provided dates with error bars in the double digits, as opposed to the triple digits of other methods. “Ten years ago we wouldn’t have been able to get this information,” Jenkins says. “We could have gotten the dates but we might not have been able to prove the coprolites were from people.”
The new technologies have not only revolutionized the study of coprolites, but also have changed how archaeologists find and handle coprolites. They have to be more careful not to contaminate the samples; they wear gloves, use face masks and limit who has access to material, Jenkins says. One of Jenkins’ greatest challenges was to track down and obtain a DNA sample from the 55 people who came into contact with the cave coprolites to rule out modern contamination. In 2007, Jenkins returned to the Oregon caves and retrieved uncontaminated coprolites, but in order to ensure there is no modern DNA, he plans to go back in late 2008 with a team dressed as if they were heading into a biohazard zone.
DNA contamination is not a problem for Chin and other researchers who study more ancient coprolites. (Nor is odor a problem; in younger, desiccated scat, the odor comes back and researchers have to work with the deposits under a fumigation hood.) Chin does, however, take advantage of high-tech tools. On a massive deposit from a Tyrannosaurus rex, she used X-ray fluorescence and microprobe analysis to confirm the chemistry of the bone and other constituents, and she is in the early stages of a CT scan of the Maiasaura coprolite.
Most coprolite research, however, involves studying thin sections under a microscope. Under magnification, researchers have found pollen grains, muscle tissue, fossilized plant byproducts called phytoliths, plant spores, bacteria and bone fragments. For example, Chin’s study of a T-rex’s king-sized coprolite relied on microscopic bone fragments to show for the first time that the dinosaur king pulverized its victims’ bones. More recently, Indian and Swedish researchers found grass phytoliths in dinosaur coprolites, further supporting the idea that dinosaurs and grasses coexisted.
“There was a period when people didn’t think about the value of coprolites, but this is starting to change,” Chin says. Nonfecal-focused paleontologists may still giggle at what Chin and her fellow coprologists study, but now they take the work much more seriously.