The Cerutti Mastodon, found near San Diego, shows signs of being butchered 130,000 years ago—but by who? Or what?

California’s highway State Route 54, skirting southeast of San Diego, doesn’t seem like it would be the catalyst for challenging some of the longest-held ideas about human evolution and our spread across the planet. And yet, in 1992, along SR 54’s ribbons of asphalt and exit ramps to malls, taco joints, and subdivisions, road-widening construction unearthed a fossil that could rewrite the human story—if scientists ever stop arguing about it.

Here, 130,000 years ago beside the future site of SR 54, a young mastodon perished. There’s nothing uncommon about that—these heavily-built, distant relatives of modern elephants were found throughout much of North America at the time. Paleontologists don’t know how the mastodon died, but there is evidence preserved in its bones, and in rocks found nearby, that the animal’s carcass may have been butchered by humans. There’s just one problem with this scenario. Most scientists agree: Homo sapiens left our ancestral homeland of Africa less than 100,000 years ago, and arrived in the Americas only in the last 15,000–25,000 years, as the last ice age ended and travel from Asia and the land bridge known as Beringia, into Alaska and Canada, became possible.

So who—or what—made a meal out of that mastodon?

The fossil is now known as the Cerutti Mastodon, after the late paleontologist Richard Cerutti, who recognized the significance of the bones as they were uncovered during the highway expansion project. Greater San Diego was growing rapidly at the time, and so was its infrastructure. Previous highway projects had turned up a wealth of fossils, from ancient walruses to dinosaurs, and Cerutti worked on behalf of the San Diego Natural History Museum as a site monitor, on the lookout for more discoveries. But he wasn’t expecting this.

California State Route 54 during the early ’90s expansion project; the Cerutti Mastodon site is at the far left of the image. Courtesy San Diego Natural History Museum

Cerutti was initially excited because he thought the fossil belonged to a mammoth. However, further excavation over several months revealed the distinctive teeth of its close relative, the mastodon—and turned up strange things neither Cerutti nor his colleagues could explain.

The heavy, massive limb bones of a mastodon are not easy to break, and specific fracture patterns on the Cerutti specimen were not consistent with natural processes, such as being tumbled in river rapids. There was also the curious arrangement of the bones. Two broken femurs appeared to be placed side by side, and one of the animal’s tusks was almost vertical, as if stuck upright in the sediment like a flagpole.

There were few rocks found in the silty sediment around the bones. However, some of the isolated rocks the team did uncover appeared to have been intentionally shaped and then used to smash something.

Cerutti and his colleagues believed that the site had all the signs of being used by humans to process an animal carcass—but that it was simply too old to fit into any recognized model for the arrival of humans in the Americas.

Who—or what—made a meal out of that mastodon?

The timelines for when Homo sapiens left Africa, and when they arrived in the Americas, are two of the most contentious issues for scientists piecing together the human story. To challenge either—never mind both at once—without conclusive evidence would have ended the team’s careers. Invitations to other archaeologists to examine the material were politely declined, likely for the same reason. So for more than a decade, the bones and rocks sat unremarked in San Diego’s Natural History Museum.

In the late 2000s, Steven Holen, research director for the Center for American Paleolithic Research, and Kathleen Holen, his wife and fellow archaeologist, decided to take a look. They reached the same shocking conclusion as Cerutti and his colleagues. The Holens have long advocated for an early arrival of our species to the Americas, attracting critics along the way, and were undaunted by the prospect of proposing such a wild revision to the established timeline. But first, they had to make their case.

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