Ancient mammoth bones marked by human butchering have been found in Michigan, shedding new light on the timeline of human presence in the state. The discovery was made in 2015, when soybean farmer James Bristle found an enormous rib bone on his farm just outside Chelsea. When paleontologists from the University of Michigan came to investigate, they found the skull and bones of an ancient, enormous mammoth.

Recently, the paleontologists returned to the site to see if they could uncover more bones. They found more from the same animal, as well as some surprising information suggesting that early humans had been there to eat it. Excavators found several mammoth bones at the bottom of what was once a pond, as well as three out-of-place boulders. Daniel Fisher, a paleontologist at the University of Michigan, suggested that primitive humans might have stored the meat at the bottom of the pond, intentionally placing boulders in the pond to anchor the body parts down.

Fisher explained that when you anchor animal parts in certain ponds, other animals have a hard time scavenging the material, and the bacteria in the pond will actually protect the remains from other, harmful bacteria. Fisher said he has tried this technique himself with meat from a variety of animals and never got sick from it. “It actually works much better than you might think,” he said.

Another important line of evidence is the way that the mammoth skull was cut up. Someone had accessed the pulp of the animal’s tusks and broken into the back of the skull in a way that only an intelligent butcher might. “This wasn’t the first time they’d taken apart these animals,” Fisher explained. “They didn’t just sort of wantonly bash it all up, they were interested in effective use of affected materials, as any other knowledgeable butcher would be.”

Furthermore, the marks on the skull suggest tool use. “The bone all around there has been basically broken loose—wack wack wack wack!—in a series of strikes,” Fisher explained.

This information could have an important impact on the understanding of anthropology, at least in Michigan. Previously, the oldest evidence for humans in the state dates to about 13,000 years ago, when the Clovis people were thought to be in the area and hunting with spears. However, radiocarbon dating from the Michigan mammoth points to it being more than 15,000 years old. If humans were there to cut up and eat the animal, that would alter their historical timeline.

Paleontologists at the University of Michigan plan to study the bones in more detail to find out more about what happened to this mammoth, and to the people who may have been there. While the information found in the bones has not been published in a peer-reviewed journal, Fisher feels that the evidence for human intervention is strong. The discovery of ancient mammoth bones marked by human butchering has the potential to rewrite the history of human presence in Michigan and beyond.