(CNN) The surprising discovery of mammoth fossils in a paleontologist's backyard have led to an even more unexpected finding.
The roughly 37,000-year-old remains of a female mammoth and her calf show distinct signs of butchering, providing new evidence that humans may have arrived in North America much earlier than believed.
Paleontologist Timothy Rowe first learned of the fossils in 2013 when a neighbor noticed something sticking out of a hillside on some New Mexico property belonging to Rowe.
Upon closer inspection, Rowe found a tusk, a bashed-in mammoth skull and other bones that looked deliberately broken. He believed it was the site where two mammoths had been butchered.
"What we've got is amazing," Rowe said in a statement. "It's not a charismatic site with a beautiful skeleton laid out on its side. It's all busted up. But that's what the story is."
Rowe, a professor at the University of Texas at Austin's Jackson School of Geosciences, is an expert in vertebrate paleontology and doesn't typically study mammoths or early humans. But he couldn't help but work on the research due to the discovery's location.
Two six-week excavations took place at the site in 2015 and 2016, but analysis in the lab has taken much longer and remains ongoing, Rowe said. He is the lead author of a new study providing an analysis of the site and its implications, which published in the journal Frontiers in Ecology and Evolution in July.
"I have yet to fully process the cosmic coincidence of this site appearing in my back yard," Rowe wrote in an email.
Multiple finds at the site paint a portrait of what took place there thousands of years ago, including bone tools, evidence of a fire, bones bearing fractures and other signs of animal butchering by humans.
Long mammoth bones shaped into disposable blades were used to break down the animal carcasses before a fire helped melt down their fat.
Fractures created by blunt force can be seen in the bones, according to the study. No stone tools were at the site, but researchers found flake knives made from bones with worn edges.
A chemical analysis of the sediment around the mammoth bones showed that the fire was sustained and controlled rather than caused by a wildfire or lightning strike. There was also evidence of bone that had been pulverized as well as burned small animal remains, including birds, fish, rodents and lizards.
The research team used CT scans to analyze the bones from the site, finding puncture wounds that would have been used to drain fat from ribs and vertebrae. The humans who butchered the mammoths were thorough, Rowe said.
"I have excavated dinosaurs that were scavenged, but the pattern of bone disarticulation and breakage from human butchering was unlike anything I had seen," Rowe said.
The most surprising detail about the site is that it's in New Mexico -- and previous evidence has suggested that humans weren't there until tens of thousands of years later.
Collagen taken from the mammoth bones helped the researchers determine that the animals were butchered 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, researchers said.
Scientists have debated for years when early humans first arrived in North America.
The 16,000-year-old Clovis culture is known because of the stone tools it left behind. But an increasing amount of evidence suggests that older North American sites were home to a pre-Clovis population that had a different genetic lineage. The older sites have a different kind of evidence, such as preserved footprints, bone tools or animal bones bearing cut marks older than 16,000 years ago.
"Humans have been in the Americas for more than twice as long as archaeologists have maintained for many years," Rowe said. "This site indicates that humans attained a global distribution far earlier than previously understood."
The position of the site, which is well within North America's western interior, suggests that the first humans arrived well before 37,000 years ago, according to the study. These early humans likely traveled over land or along coastal routes.
Rowe said he wants to sample the site to look for signs of ancient DNA next.
"Tim has done excellent and thorough work that represents frontier research," retired Texas State University professor Mike Collins said in a release. "It's forging a path that others can learn from and follow."
Collins was not involved with the study. He led research at the Gault archaeological site, which contains both Clovis and pre-Clovis artifacts, near Austin, Texas.
"I think the deeper meaning of early human attainment of a 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 that there are other sites of comparable age or even older that have gone unrecognized."