Fisher and Rountrey helped uncover evidence from the mastodon bones, discovered in San Diego in 1992 and dated to 130,000 years ago. Their researched showed that markings on the bones were indicative of human interference, which dramatically changes our understanding of when humans first arrived in North America. Previous estimates had humans arriving nearly 115,000 years later.

Fisher, professor of paleontology, earth and environmental sciences, ecology and evolutionary biology, and director and curator of the Museum of Paleontology, was a co-author of the paper with Rountrey, collection manager at the Museum of Paleontology, and nine other paleontologists.

"We don't know how this animal died. We don't know whether humans were part of that death. All that we know is that humans came along some time after the death, and they very strategically set up a process involving the harvesting of marrow from the long bones and the recovery of dense fragments of bone that they could use as raw material for producing tools," said Fisher.