Assessing the suitability of a new porcine dry bone scoring method for South African burial taphonomy when applied to two posthumous human skeletal samples

When a body is buried, the story of its final years is written not in words, but in the slow, silent changes that happen to the bones. This field of study, known as taphonomy, looks at how the environment—soil, water, plants, and animals—alters human remains after death. It is a crucial tool for archaeologists and forensic scientists trying to understand the context of a discovery: Was the person buried in a coffin? Was the soil acidic? How long has the body been there? To learn these lessons, researchers often turn to pigs. Because pigs share a similar body shape and fat distribution with humans, they are frequently used as stand-ins to study how bodies decompose. However, a new study from South Africa suggests that while pigs are helpful, they are not perfect mirrors for human history, and the lessons learned from them need careful adjustment when applied to actual human skeletons.

The researchers, working at the University of the Witwatersrand, set out to test a specific scoring system designed for pig bones to see if it would work for human remains. They focused on two very different groups of people from South Africa's mining history. The first group consisted of thirty individuals buried in the semi-arid Free State province, near the Koffiefontein diamond mine. These people, mostly migrant laborers from the late 1800s, were buried in six-foot-deep, unmarked graves, with the majority without coffins, in a hot, dry climate with sandy soil. The second group included thirty individuals from the Witwatersrand Deep gold mine in the temperate Gauteng region. These were indentured Chinese laborers from the early 1900s, buried in wooden coffins in a climate with more rainfall and soil that had become acidic due to mining activities.

The team began by applying the existing pig-based scoring system to the human bones. They looked for six specific types of changes: how much the bone had cracked or flaked from the weather, whether plant roots had damaged the surface, if the soil had eaten away at the bone through acidity, the color stains left by the dirt, the presence of a waxy substance called adipocere that forms in wet conditions, and any signs of animals scavenging the remains. Almost immediately, the pig system showed its limits. The human bones told a different story than the pig bones had. For instance, the pig system did not account for the unique stains left by metal objects like buttons, belt buckles, or jewelry, which were common in the human burials. It also failed to capture the specific way human bones, which have a different internal structure than pig bones, cracked and broke down over time.

To fix this, the researchers modified the scoring method. They added new categories for the unique "grave artifact" stains, such as the green or blue marks left by copper or the purple hues from chemical reactions in the soil. They also expanded the system to include natural mummification, where dry skin and tissue remain on the bone, a process seen in the dry Koffiefontein climate but not in the wetter pig studies. They added a category for fungal growth, which thrived in the damp, coffin-buried Witwatersrand group. Once these changes were made, the new system provided a much clearer picture of what happened to the human remains.

The comparison between the two human groups revealed how powerfully the burial environment shapes the final state of a skeleton. The Koffiefontein bones, buried in dry, sandy soil without coffins, were remarkably well-preserved. They showed very little sign of acidic corrosion, and some even displayed natural mummification, a result of the hot, dry air halting the decay of soft tissues. In contrast, the Witwatersrand bones, buried in acidic soil inside wooden coffins, looked very different. They were heavily corroded by the acid in the ground, exhibited fungal growth in the majority of cases, and showed extensive weathering. The wooden coffins, while protecting the bodies from animals, had created a moist, oxygen-rich microenvironment that encouraged fungi and accelerated the breakdown of the bone in the acidic soil.

The study concludes that while the pig-based scoring system is a useful starting point, it is not sufficient on its own for human archaeology. The differences in bone structure between species, combined with the vast variations in burial depth, soil chemistry, and climate, mean that a one-size-fits-all approach fails to capture the full history of human remains. By refining the scoring method to include human-specific factors like artifact staining and mummification, the researchers have created a more accurate tool. This new framework allows scientists to read the subtle, chemical, and physical stories written on the bones of the past, revealing the specific conditions of the graves and the lives of the people who were buried there.