Archaeologist and biostatistician Erik Otárola-Castillo leads the research team that used 3-D imaging, shape analysis and Bayesian statistics to identify butchery cut marks with an 88 percent success rate in classifying butchery behaviors. The 3D imaging technology is similar to what engineers use to measure scratches on microchips and surgical blade sharpness. The findings are published in the Journal of Archaeological Science. Credit Purdue University photo/Mark Simons

Scientists are looking at animal bone cuts to try to answer some unknown questions about human evolution.

A team led by Purdue University researchers have developed a new statistical method that is used with 3D imaging and shape analysis to accurately measure animal bone cut marks made by prehistoric human butchery.

“This approach represents a major improvement in accuracy when compared to many archaeological methods, and improving this technique will help us get the human evolution story correct,” Archaeologist and biostatistician Erik Otárola-Castillo said in a statement. “By strengthening quantitative methods to evaluate archaeological evidence, we will be able to learn more about early humans much more quickly.

“In archaeology, butchery marks on animal bones are a key piece of evidence used to answer questions about food acquisition in prehistoric hunter and gatherer populations,” he added.

Human-made stone tools leave cut marks on animal bones through butchery, including bones from sheep, deer or bison.

The cut marks can range from one to five centimeters. However, the depth of the cuts are often miniscule, measuring at approximately 1/15th of a millimeter.

The researchers used more than 40 cuts (a 90-degree incision angle) and slices (a 45-degree incision angle) made by volunteer butchers on sheep bones using stone tools.

They then measured the cuts with a profilometer—a 3D microscope that measures topography, roughness and layer thickness in the micro and nanometer ranges.

After measuring the cuts, the researchers conducted a 3D shape and size analysis of the curves and surfaces to compare the cut marks.

“Once the digital data were compared, we used Bayesian statistics, which provide a quantitative measure of scientific believability,” Otárola-Castillo said. “For example, given the evidence, the probability of accurately determining the identity of a mark on a bone is 88 percent in this case.”   

Archaeologists often attempt to distinguish between cut marks made by a human's stone tool, which leaves a "V" shape, and other damage, such as trampling by a hooved animal, which can leave marks with more of a "U" shape.

For more than two centuries, archaeologists have attempted to identify butchering marks. The current techniques include naked eye qualitative assessments and high-powered microscopy including scanning electron microscopy or micro-photogrammetry.

The study was published in the Journal of Archaeological Science.