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In Dental Plaque, Archeologists Extract Insight into a Prehistoric Desert City

photograph by HJPD. Paquime, or Casas Grandes – located 250 miles due west of Marfa in present-day Chihuahua – was a thriving city between 1200 and 1450 CE. Thousands lived in this urban oasis, in multi-story adobe apartments – the remains of which can be seen at the site today.

“History” is said to begin with the written word. And that can make us think that, in the absence of a written record, human life was somehow static or unchanging. But the human journey has always been characterized by innovation and experiment, by triumph and catastrophe, by cycles of growing complexity and collapse. 

In our region, nothing illustrates that like the site known as Paquime, or Casas Grandes. Beginning around 1200 CE, in what's now Chihuahua, 250 miles due west of Marfa, the region's Indigenous people built a “water city in the desert.” In reservoirs, canals and terraced fields, they marshaled the waters of the Casas Grandes River and of perennial springs. Thousands lived in multi-story adobe apartments, in an urban oasis. They tracked annual cycles from a solar observatory, and built monumental ceremonial mounds of earth and masonry – including one of the horned or feathered serpent known as Quetzalcoatl. They imported pottery from the El Paso area, and their ceramics are found in the Big Bend. Recent DNA analysis proves that prehistoric West Texans had close kin in this desert city. 

As an archeological site, Paquime rivals anything in the Southwest. But it's been relatively little studied. Now, there's a wave of new research. At Paquime, scientists are extracting insight from unlikely places – and revealing the complexity of the Chihuahuan Desert's human past. 

Dr. Michael Searcy is an archeologist at Brigham Young University. 

“I love all these new methods that we're using,” Searcy said, “like ancient DNA, micro-botanical analysis – looking at these tiny particles of plants that are found in our tartar. We love that these people didn't brush their teeth, or at least it doesn't appear so – because it's more data for us.”

With PhD student Daniel King, he led a study of “dental calculus” – fossilized plaque, also called tartar – from the teeth of ancient Paquime residents.

Contemporary students of Paquime all build on the work of archeologist Charles Di Peso. Di Peso conducted pioneering excavations here, beginning in 1959 – and published his findings in an eight-volume report.

That report included wonders. The people of Paquime, Di Peso found, had raised scarlet macaws – tropical birds whose bright feathers were used in ritual. They'd built I-shaped ball courts – strikingly similar to those found far to the south, in Mayan country. Di Peso discovered an underground shrine – stairs had been carved 50 feet into the earth, down to the water table, and were lined with offerings. 

There were terraced fields – clearly the “Paquimeans” were farmers. There were massive earth ovens – used, perhaps, to roast agaves for feasting and fermentation. And Di Peso found many grinding stones – like those still used today for grinding corn. 

But as far as actual plant remains – or direct evidence for the diet at Paquime – he found little. Searcy proposed the dental calculus study to King, to correct that.

“We have very little information about plants,” Searcy said. “I told him it would be a great way to fill a gap about the diet of these people, by looking at what they were actually putting in their mouths.” 

With permits and grant funding, they collected plaque from 110 individuals buried at Paquime. They sent those samples to Chad Yost, who specializes in the analysis of microscopic plant remains.   

Yost's findings exceeded their expectations.

Corn, indeed, was a mainstay. But Yost could also see that Paquime people had soaked or boiled their corn in an alkaline solution – to remove the hard, indigestible shell that surrounds each kernel. It's a process known as “nixtamalization” – and it's been practiced in the Americas for at least 3,000 years. It's the first step in creating masa – the corn-meal base for tortillas and tamales. Nixtamalization improves not only taste, but corn's nutritional value.

Then, Yost found spores of “corn smut,” a fungus that grows on corn. Like mushrooms, corn smut has a rich, earthy taste. The Spanish observed it in the Aztec diet, and it's still served today – as huitlacoche – in fine Mexican cuisine.

One of Yost's most remarkable findings was the presence in the plaque of “marine diatoms.”

“These are microorganisms that only live in salt water,” Searcy said, “and likely came either from people eating food that was transported in, like fish or shellfish, or these were people who lived on the coast and came in and within months died and were buried. So we found a ton more than we ever imagined.”

Early Spanish accounts indicate that the region's Native people enjoyed fermented beverages. But it's hard to find in the archeological record. Yet in plaque samples from several individuals, Yost found evidence for the consumption of corn beer. 

The individuals in question had been victims of human sacrifice.

“They were getting pretty sloshed probably at times,” Searcy said, “maybe right before they were sacrificed. It would be really convenient – I'd rather be inebriated before I got killed.”

The dental calculus can't tell the full story of the Paquime menu. It's not in the plaque – but archeologists know from other analysis that meat likely composed about 20 percent of the diet here. The bones of rabbits and deer, of pronghorn and bison, have been recovered at Paquime. But the study is a powerful example of how new techniques are deepening archeological insight. And it gives us a vivid look into city living in our region's prehistoric past.

Drew Stuart is the producer for the Marfa Public Radio series Nature Notes.