Sunday, January 25, 2015

The Copious Little Coprolite: A Tale of Underrated Informants

As you may or may not already know, a great deal of my dissertation work focuses on the analysis of desiccated human feces (i.e. "coprolites"). These remains can come from archaeological sites such as caves and trash middens, or from direct human contexts such as mummified intestines or even burials in some special cases (e.g. Nivelles). Coprolites most often form in arid environments, preserving within them a vast amount of information about their depositors' diets, medicinal plant usage, and pathogens.  By analyzing these tiny cornucopias of data, we are able to learn not only what people were eating and what was eating them, but also to use these data to elucidate patterns of human behavior as our ancestors interacted with the world around them. Today, we are going to pay homage to something that doesn't often get the recognition that it deserves...the copious little coprolite.

A coprolite from Hinds Cave, Texas.
A Brief History of Coprolite Analysis
The word "coprolite" began as a descriptor of mineralized dinosaur feces used for the first time by a paleontologist named William Buckland in 1829. By the 1960s, the term had been applied to other fecal forms preserved via desiccation in addition to mineralization and was being used to describe fecal materials from archaeological contexts  in addition to paleontological contexts. There have been three distinct phases in this history of coprolite analysis stretching from 1829 up to the present.

The first phase (1829-1960) began with the birth of the term "coprolite". The value of human coprolites was not recognized until 1896, when a botanist named John William Harshberger suggested that looking at seeds in coprolites could reveal information about ancient diets. The early 1900s that followed Harshberger's suggestion saw researchers examining coprolites for other plant remains, like leaves and twigs, in addition to faunal remains, such as the tiny bones found in fecal deposits from a wide range of archaeological contexts. By the 1950s, people began looking more at the neat stuff in human coprolites. They started looking at hair and feathers as well as shell fragments and insect remains. Today, the study of "macrofossils" (macroscopic plant and animal tissues found in coprolites) is a crucial element of coprolite analysis.

Eventually, people began seeking smaller sources of evidence that today we call "microfossils" (things like pollen, starch granules, and our beloved parasite eggs). The first evidence of parasitism in the prehistoric New World came from whipworm (Trichuris trichiura) eggs found in an Incan mummy in 1954. This began the transition of coprolite analysis into the second phase (1960-1970). This phase saw the development of specialized techniques for examining microfossils and laid the foundations for later expansion.

The superstar researcher of the second phase was indisputably a man by the name of Eric Callen. Callen is known to many as the first true coprolite specialist. He completed three major analyses of coprolites recovered from New World archaeological sites and was working on a fourth when he died tragically in 1970. Despite being ridiculed by colleagues for his interest in coprolites (which were regarded as useless by researchers of that time), Callen persevered to become a legend in a now much more respected field. He developed methods for rehydration (a crucial first step in analyzing coprolites) and standardized other techniques for evaluating fecal deposits.

Various pollen grains
A wealth of other researchers also worked on coprolites during this second phase. It was during this era that pollen analysis was integrated into coprolite analysis. These early studies yielded incredible insights into the diets, medicinal plant usage, and even seasonal site occupations of prehistoric peoples of the New World. This era also saw the flickering of parasite studies that would ignite the third phase.

The current phase of coprolite analysis began in 1970. This phase has been characterized by both refined methods of analysis and by the expanse of these analyses into more interdisciplinary realms. Coprolite analysis grew to be applied in a broader sense to archaeological questions beyond the direct discoveries of dietary remains and evidence of diseases in antiquity. Techniques for quantifying macrofossils were developed over the course of a decade. Macrofossil identification techniques were also becoming more sophisticated and researchers began comparing coprolite data from various archaeological sites to one another. Pollen analyses also became more refined as methods for quantification and interpretation were tested and standardized. The study of phytoliths, fungal spores, and starch granules also became integrated into coprolite analysis. This allowed for more rigorous and fruitful assessments of nutrition through time and space.
A variety of phytoliths from the Tangue site in China.
{A–c = rice bulliform; d–g = rice double peaked; h, i = phytoliths from broomcorn millet husk;
j = long saddle; k = scutiform-bulliform from reed; l = common bulliform; m = Cyperus type;
n = trapeziform sinuate (tooth type); o = woody phytolith}
Which brings us up to the birth and subsequent growth of the field of archaeoparasitology. With foci in Brazil, Canada, Chile, England, Germany, Peru, and the United States, analyzing coprolites for evidence of parasitism grew exponentially. From the late 1970s right up through the early 1990s, methods for extracting and quantifying parasite eggs were developed. From the refinement of these methods came the ability of researchers to begin examining epidemiology of the past through the lens of parasitism. The following decades would usher in the integration of molecular techniques for finding evidence of parasitism that could not be seen with the naked eye. Studies using PCR and ELISA would revolutionize coprolite analyses to give researchers an even broader perspective of epidemiology in antiquity.

What's in a Coprolite and What Can They Teach Us?
As you likely gathered from the above, coprolites can treasure troves of taxonomic data. Breaking these into discrete components is how researchers conduct analysis, but only by re-combining dataset after discrete analyses are we able to get the full story that coprolites are trying to tell us. Reinhard and Bryant (1992) broke coprolites into their components in the following way:

1) Biological (Bacteria, Viruses, Fungi, Parasites, Insects, Pollen, Phytoliths, Macrobotanicals, and Macrofaunal Remains)

2) Mineral and Chemical (Sand, Grit, and Flakes, Charcot-Leyden Crystals, and Chemical Components)

All of these different elements that can be recovered from coprolites give dimension to the overall analysis. Taking in discrete datasets examining coprolites for a variety of components and synthesizing the information leads to the emergence of the bigger picture. By finding the eggs of fish tapeworms and tiny fish vertebrae in a land-locked population's coprolites, we can begin to understand prehistoric patterns of trade between this population an a coastal population. By finding the minuscule bones of rodents in the coprolites of cave dwellers, we can begin to picture the resource utilizations and ecological displacements that contributed to the origins of now-established zoonotic diseases among human populations today.

It is obvious, though not always intuitive for some, that diet and disease are intrinsically linked. This is true for the modern world as it was true for populations of the past. Understanding the nature of the diet-disease relationship comes to light by combining the data one can gather from coprolites. These little packets of poop are warehouses of information for understanding such relationships. They not only provide direct evidence (e.g. parasite eggs or pollen grains) but also proxy evidence (e.g. neotropical parasites found in pre-clovis coprolites from the pacific northwest point towards coastal human migration patterns into the new world).

Coprolite analysis is a vital aspect of archaeoparasitology, but also reaches far into other disciplines. Such studies are important for dietary reconstructions, understanding the interactions of people and their environments, and inferring aspects of early human behaviors. Advances in the areas of medicine, food technology, and environmental adaptation can be reflected by the composition of macrofossils and microfossils present in coprolites.

Today, coprolite analyses are being used to examine the origins of many diseases that plague modern societies. Diseases as different in their etiologies as Chagas' disease (caused by a parasitic protozoan) and diabetes (a metabolic disorder). Tracing the origins of such diseases is no small or simple task, but can be done through the analysis of the copious little coprolites that await researchers interesting in unveiling their stories.

The Moral of the Story
I could go on with a long, eloquent speech doting on the awesomeness of coprolite analysis and droning on about how excited I am about my own dissertation work with these remains, but I think by now you've probably read enough to wet your appetite for exploring coprolite analyses on your own. (Or, at least I hope I've so piqued your interest.) Instead, I will leave you with a somewhat crude, but appropriate message: Don't let anyone give you sh*t for liking coprolites. Seriously, people are quick to put down great work that originates from looking at things that some deem as "gross". (This is typically due to their own ignorance as to the significance of said work.) As a parasitophile, you are probably no stranger to the disgusted reactions of people who don't understand the value of parasitiology. But we don't do it for them, now do we? We do it for us. We do it to better understand the intricacies of the world around us. We do it because our passion knows no bounds. As a coffee cup that sits in an unnamed parasitology lab states: Don't let the bastards get you down!

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