Jose Luis Gonzalez / Reuters

In the Mayan city of Copán, at the base of a 30-meter-tall pyramid, there’s a beautiful stone slab known as Altar Q. The altar is square, and each of its meter-wide faces preserves carvings of four of the city’s 16 rulers, including its final king, Yax Pasaj Chan Yoaat, who commissioned the structure in 776. It was as much propaganda as historical record. Though Yax Pasaj wasn’t part of a dynastic bloodline himself, the altar shows him receiving the scepter of kingship from Copán’s founding ruler, thus proving that he was worthy of ruling. The altar was a statement of his legitimacy.

The jaguars probably helped.

There’s a crypt immediately in front of the altar, which contained the bones of several birds, and 16 big cats—jaguars and pumas (cougars) packed so tightly that the people who first excavated them referred to them as “jaguar stew.” It’s likely that these animals were sacrificed on the altar as emblems of power, one cat for each king.

“It’s hard to imagine this very elaborate ritual in one of the hardest times for the Copán dynasty,” says Nawa Sugiyama, an archaeologist at George Mason University. Yax Pasaj was the last person to rule the city before it collapsed, and his reign was one of political turmoil and environmental degradation. Amid that turmoil, he somehow managed to acquire 16 big cats, even though the surrounding valley was too small to house more than five jaguars, and even though these beasts are hard to find, much less to capture.

Sugiyama thinks she knows how he did it. By analyzing the chemicals within the buried cat bones, she and her colleagues showed that jaguars and pumas likely came to Copán from distant regions and were kept in captivity for most of their lives. The city effectively had its own zoo, which was part of a wide trade network that sucked in wildlife from a larger area. For three centuries, wild animals—including the most formidable carnivores around—were brought in, housed, fed, and eventually used in ritual ceremonies.

“These people were interacting head on with some of the most powerful predators in the landscape—and that’s a feat we don’t see in many civilizations,” says Sugiyama. “We’ve always assumed that people in Mesoamerica only had the dog and the turkey—and camels and guinea pigs further south. But I think the dynamics between humans and animals [in the region] were much deeper.”

“We think of zoos and captive animals as a very modern thing, and also tend to think that animals in the past are merely food sources or beasts of burden,” adds Kelly Knudson, an anthropologist from Arizona State University. “This study helps us rethink both of these assumptions.”

In the 16th century, Moctezuma, ruler of Tenochtitlán, kept a famous private zoo full of thousands of animals. But in 2015, Sugiyama found evidence that Mesoamericans kept wild animals in captivity much earlier. She analyzed the remains of jaguars, pumas, golden eagles, and wolves that had been entombed in the great pyramids of Teotihuacan, Mexico, between the first and sixth centuries. Many of these showed signs of debilitating injuries, such as broken wings and legs. “These would have been fatal injuries in the wild,” says Sugiyama, who concluded that the animals had most likely been kept in captivity. By contrast, the cat remains from Copán bore no signs of such injuries. So Sugiyama turned to a different method.

Captive animals are more likely to be fed with agricultural crops like corn (or, in the case of big cats, with corn-fed birds). Compared with wild grasses, corn has unusually high levels of carbon-13—a form of carbon that’s much rarer and slightly heavier than the more common carbon-12. By measuring carbon-13 in the Copán bones, Sugiyama could tell if the cats had been raised on an artificial diet.

First, she analyzed a group of bones from the so-called Motmot tomb, which was constructed in the year 435. Within were the bones of a young woman, sitting cross-legged on a reed mat, three more human skulls, two deer, several birds and turtles, and the complete skeleton of a puma. The woman was likely a shaman, who was buried with her animal counterpart—the puma. And that cat, Sugiyama showed, had clearly been in captivity for a long time. It was getting more corn in its diet than a turkey found in the same tomb.

Sugiyama also measured another isotope in its bones: nitrogen-15, which exists at higher levels in animals further up the food chain. “The nitrogen level tells me that the puma hadn’t turned vegetarian,” says Sugiyama. “It was just eating a lot of corn-eating domestic animals.”

She applied the same techniques to the Altar Q remains, and got the same results. The cats there had been eating a lot of corn-fed creatures. There’s no evidence that they were bred in captivity or had been fully domesticated. Instead, Sugiyama thinks they were captured as cubs, and raised in the urban metropolis as eventual sacrificial victims. “The high carbon-13 content in their teeth suggests that when these were erupting, they were already in captivity,” she says.

“It’s absolutely solid work,” says Erin Thornton, an anthropologist at Washington State University who specializes in isotope analysis. “With animal remains from Mesoamerica, it’s very hard to tell if you’re dealing with a captive animal from bones alone. Stable isotopes are really the only way to tell if an animal was removed from the wild and put under human management.”

Where were the jaguars and pumas coming from? To find out, Sugiyama turned to yet another isotope—oxygen-18. Its levels vary depending on the water source that an animal drinks, and so changes with climate and geography. And since the jaguar and puma bones from Copán contain a wide range of oxygen-18 values, these cats likely came from afar and were perhaps reeled in via an expansive trade network.

It’s not a slam-dunk case, Sugiyama admits. Oxygen isotopes are harder to interpret than carbon or nitrogen ones, and big cats tend to roam over large ranges anyway. Yet more isotopes—strontium-86 and strontium-87—could provide cleaner answers, as their levels are more clearly tied to the bedrock of different areas. That’s what Sugiyama intends to measure next.

These isotopes “have really been a game changer,” she says. “I would never have been able to look at the Copán material and known that they were captive. You might have eaten a lot of corn, and unless you broke a limb, an archaeologist would never know. Chemically, though, it’s a very different ball game. It’s such an exciting time to be doing archaeology.”

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