A pile of ribs, broken cranial bones, a molar, bone fragments and stone cobbles were discovered during an excavation of a site where maammoths were butchered.

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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.

The excavation site contained fractured bones from a mammoth skull, spine and ribs.

Timothy Rowe/The University of Texas at Austin

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.