(CNN) — The startling discovery of mammoth fossils in a paleontologist’s backyard led to an even more unexpected find.
The remains of a female mammoth and her calf, some 37,000 years old, show clear signs of carnage, providing new evidence that humans may have arrived in North America much earlier than previously thought.
Paleontologist Timothy Rowe learned of the fossils in 2013, when a neighbor spotted something sticking out of a hillside on a New Mexico property Rowe owned.
Upon closer inspection, Rowe found a tusk, a sunken mammoth skull, and other bones that appeared to be deliberately broken. He believed that it was the place where two mammoths had been butchered.
“What we have is amazing,” Rowe said in a statement. “It’s not a charismatic site with a beautiful skeleton laying on its side. It’s all smashed up. But that’s the story.”
Rowe, a professor at the Jackson School of Geosciences at the University of Texas at Austin, is an expert in vertebrate paleontology and doesn’t usually study mammoths or early humans. But he couldn’t help but work on the investigation because of the location of the discovery.
Two six-week excavations were conducted at the site in 2015 and 2016, but laboratory analysis has taken much longer and is ongoing, Rowe said. Rowe is the lead author of a new study providing an analysis of the site and its implications, published in the academic journal Frontiers in Ecology and Evolution in July.
“I have yet to fully process the cosmic coincidence of this showing up in my backyard,” Rowe wrote in an email.
The site’s many finds paint a picture of what happened there thousands of years ago, including bone tools, evidence of a fire, broken bones and other signs of human butchery of animals.
Long mammoth bones shaped like disposable knives were used to break up animal carcasses before fire helped melt their fat.
According to the study, fractures created by brute force are observed in the bones. There were no stone tools at the site, but the researchers found scaling knives made from bone with worn edges.
A chemical analysis of the sediment surrounding the mammoth bones showed that the fire was sustained and controlled and not caused by wildfire or lightning. There was also evidence of pulverized bones and burned remains of small animals, including birds, fish, rodents and lizards.
The research team used CT scans to analyze the bones at the site, finding puncture wounds that would have served to drain fat from ribs and vertebrae. The humans who butchered the mammoths were thorough, Rowe said.
“I have excavated dinosaurs that were eaten by scavengers, but the pattern of disarticulation and breaking of the bones produced by human carnage was unlike anything I had seen,” Rowe said.
The most surprising detail of the site is that it is located in New Mexico, and previous tests have suggested that humans were not there until tens of thousands of years later.
Tracing the first human steps
Collagen extracted from mammoth bones helped researchers determine that the animals were slaughtered at the site between 36,250 and 38,900 years ago. This age range makes the New Mexico site one of the oldest that ancient humans created in North America, the researchers said.
Scientists have debated for years when the first humans arrived in North America.
The 16,000-year-old Clovis culture is known for the stone tools it left behind. But a growing body of evidence suggests that the oldest sites in North America were home to a pre-Clovis population that had a different genetic lineage. The older sites have a different kind of evidence, like preserved tracesbone tools or animal bones with cut marks from more than 16,000 years ago.
“Humans have been in the Americas for more than twice as long as archaeologists have kept for many years,” Rowe said. “This site indicates that humans reached a global distribution much earlier than previously believed.”
The position of the site, which is within the western interior of North America, suggests that the first humans arrived well before 37,000 years ago, according to the study. These early humans probably traveled overland or along coastal routes.
Rowe said he wants to sample the site to look for signs of ancient DNA next.
“Tim has done an excellent and thorough job that represents cutting-edge research,” retired Texas State University professor Mike Collins said in a statement. “He is forging a path that others can learn from and follow.”
Collins was not involved in the study. He led research at the Gault Archaeological Site, which contains Clovis and pre-Clovis artifacts, near Austin, Texas.
“I think the deeper meaning of early human achievement of global distribution is an important new question to explore,” Rowe said. “Our new techniques provided nuanced evidence of a human presence in the archaeological record, and I suspect there are other sites of comparable or even older age that have gone unrecognized.”