HUMAN beings domesticated several of the animals they encountered during their colonisation of the Americas—notably guinea pigs, llamas and turkeys. But they brought only one such tame companion with them when they first crossed from Siberia to Alaska. This was the dog. And, though genetic studies show that most modern dogs in the Americas are descended from post-Columbian European imports, a few breeds preserve their ancient ancestry.

These relics include Chihuahuas, from Mexico and Central America. Chihuahua-like skeletons have been found in many Mesoamerican archaeological sites. But what role these tiny dogs played in pre-Columbian society has been unclear. It is a little less unclear now, though, thanks to a study just published in the Proceedings of the National Academy of Sciences by Ashley Sharpe of the Smithsonian Tropical Research Institute in Panama. In it Dr Sharpe shows that the Maya, a Mesoamerican people who flourished between the eighth century BC and the tenth century AD, traded dogs over long distances, and that these dogs may have been involved in religious ceremonies. The study also hints that the Maya kept big cats—either jaguars or pumas—again for religious purposes.

Dr Sharpe came to these conclusions after studying roughly 25,000 animal bones collected in and around Ceibal, an abandoned Maya city in modern-day Guatemala. Most of those bones came from what appear to have been rubbish dumps on the outskirts of the city. Some, however, were found in its ceremonial centre. Altogether, from all sites, she and her colleagues identified bones of white-tailed deer, peccaries, two species of turkey, some large cats (they were unclear whether these were jaguars or pumas), opossum and tapirs. And dogs. As with other Mesoamerican sites, these dogs resembled modern Chihuahuas.

To find out more about the remains, canine and otherwise, the team subjected 78 of the bones, each from a different skeleton, to two sorts of isotopic analysis. First, they looked at the bones’ carbon composition. Most carbon atoms have 12 neutrons in their nuclei, but about 1% sport a thirteenth. In plants, the ratio of 12C to 13C depends on which of two forms of photosynthesis (C3 or C4) the plant employs. C4 plants have more 13C than do C3 ones. This ratio is then passed on to animals that eat the plants in question, making it possible to guess those animals’ diets from molecules in their remains.

In the wild, only about 5% of plants use C4, but that is not true of crops. In particular, maize, the main cereal in pre-Columbian America, employs C4 photosynthesis. Pre-Columbian people therefore had bones enriched in 13C. And so, Dr Sharpe discovered, did the dogs at Ceibal. All 26 of the dog specimens she analysed had 13C values double those found in the deer, the peccaries, the tapirs and the opossum.

That is interesting, but not entirely surprising. It suggests the dogs were eating either maize, or animals fed on maize, or both. This will surely have been true, whether they were pets or feral animals dependent on human refuse. Three of the five turkeys, too, had high 13C values—again, no surprise. Intriguingly, however, one of the big cats had also eaten a lot of 13C. And this cat’s bones had been excavated from the central ceremonial area.

Nor is carbon the only element of interest to archaeologists. Strontium fascinates them, too. Like carbon nuclei, those of strontium have two stable isotopes. Unlike carbon, the ratio of these isotopes in living things reflects local geology rather than photosynthesis. Dr Sharpe’s analysis of strontium in the animals’ teeth showed that two of the dogs had not been born and raised locally. One had come from the highlands near what is now Guatemala City, almost 200km away. The other was from a place in the foothills of those highlands, on what other evidence suggests was a trade route from the highlands to Ceibal. And the dogs concerned were both from the ceremonial area.

To judge by both their provenance and the locations of their skeletons, these dogs were somehow special. And so was the isotopically anomalous big cat, which had clearly been fed on animals (perhaps turkeys) that had, themselves, fed on maize. Maybe all three were just priests’ pets. Or maybe they formed part of some ritual. If that was the case, it is unclear whether they were objects of veneration or sacrifice. With the Maya, it could have been either.

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