UM pair aid research on when humans reached N. America
Archaeological evidence points to human arrival in North America less than 15,000 years ago but a provocative discovery involving a prehistoric mastodon is prompting some scientists to dramatically push back the time frame – by 100,000 years.
According to a paper published Wednesday in the journal Nature that includes two University of Michigan researchers, a stone tool and anvil unearthed during the discovery of the mastodon bones hint that relatives of humans may have been here much earlier than previously thought.
San Diego Natural History Museum paleontologists discovered the mastodon bones and tools in 1992 in an area where a highway was being built in southern California, now known as the Cerutti Mastodon site. Researchers attempted to date the fossils that eventually showed humanlike behavior from about 130,000 years ago, when bones and teeth of an elephant-like mastodon were evidently smashed with rocks.
The earlier date means the bone-smashers were not necessarily members of our own species, Homo sapiens. The researchers speculate that these early Californians could have instead been species known only from fossils in Europe, Africa and Asia: Neanderthals, a little-known group called Denisovans, or another human forerunner named Homo erectus.
“This discovery is rewriting our understanding of when humans reached the New World,” said Judy Gradwohl, president and CEO of the San Diego Natural History Museum, whose paleontology team discovered the fossils, managed the excavation and incorporated the specimens into the museum’s research collection. “This raises intriguing questions about how these early humans arrived here and who they were.”
Until recently, archaeologists acknowledged that the oldest documented human sites in North America are about 14,000 years old. But California field paleontologist Richard Cerutti discovered the fossils that had been deposited much earlier.
UM paleontologist Daniel Fisher, a co-author of the Nature paper, said several lines of evidence from the Cerutti Mastodon site point to “one interpretation that is almost unavoidable because of the way these different lines of argument interlace.”
“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, who has been excavating mammoths and mastodons in the Great Lakes region for 38 years and who also has worked on woolly mammoth remains in Siberia for about 20 years.
Adam Rountry, collection manager at the UM Museum of Paleontology, led the effort to create digital 3-D models of bone and stone specimens suggesting human association at the Cerutti site. They can be viewed at the University of Michigan Online Repository of Fossils.
“The models were immensely helpful in interpreting and illustrating these objects,” he said. “We were able to put together virtual refits that allow exploration of how the multiple fragments from one hammerstone fit back together. The 3-D models helped us understand what we were looking at and to communicate the information much more effectively.
“I think the models are important in terms of supporting the paper because they allow anyone to look at this evidence in much the same way the co-authors did. It’s fine to be skeptical, but look at the evidence and judge for yourself.”
Those not connected with the study offered a range of reactions.
“If the results stand up to further scrutiny, this does indeed change everything we thought we knew,” said Chris Stringer of the Natural History Museum in London. Neanderthals and Denisovans are the most likely identities of the visitors, he said.
But “many of us will want to see supporting evidence of this ancient occupation from other sites, before we abandon the conventional model of a first arrival by modern humans within the last 15,000 years,” he wrote in an email.
Some were skeptical that the rocks were really used as tools. Vance Holliday of the University of Arizona in Tucson said the paper shows the bones could have been broken the way the authors assert, but they haven’t demonstrated that’s the only way.
Richard Potts of the Smithsonian Institution’s National Museum of Natural History said he doesn’t reject the paper’s claims outright, but he finds the evidence “not yet solid.” For one thing, the dig turned up no basic stone-cutting tools or evidence of butchery or the use of fire, as one might expect from Homo sapiens or our close evolutionary relatives, he said.
The Associated Press contributed.