30 April, 2017
Jared Beeton, professor of physical geography, contributed to the research on the Cerutti Mastodon site and is one of 11 authors on the article. At the archaeological site, which was first unearthed in the 1990s, researchers discovered pieces of limb bones and teeth from the mastodon, an enormous extinct creature distantly related to the elephant. But a study almost 25 years in the making in this week's Nature finds that the 130,000-year-old bones of a mastodon, an extinct relative of the mammoth, unearthed in California were split open with blows from rocks.
James Paces, a geologist with the U.S. Geological Survey, used radiometric dating methods to determine that the mastodon bones were 130,000 years old.
The finding would radically rewrite the understanding of when humans reached the New World, through some scientists not involved in the study voiced scepticism.
The fragmented mastodon remains were first discovered in late 1992 by study co-author Richard Cerutti of the San Diego Natural History Museum, during routine paleontological monitoring work at a California Department of Transportation freeway expansion project in southern San Diego.
Until recently, the oldest records of human sites in North America generally accepted by archaeologists were about 14,000 years old.
The find is a controversial one as there has been a general consensus among paleontologists and anthropologists that humans made the journey to North America roughly 15,000 years ago.
Shattered bones found on a construction site in California uncovers new possibilities of human history in the Americas. This is not that uncommon a find per se - we know early humans ate mastodons all the time.More news: 'Huge' explosion at Damascus airport
"As humans moved out of Africa and across the world, they took this type of technology with them", Steve Holen, the study's lead author and director of research at the Center for American Paleolithic Research in South Dakota, told Nature.
"The bones and several teeth show clear signs of having been deliberately broken by humans with manual dexterity and experiential knowledge", Holen said in a press release.
"This breakage pattern has also been observed at mammoth fossil sites in Kansas and Nebraska, where alternative explanations such as geological forces or gnawing by carnivores have been ruled out", Holen added. It could not have been the work of carnivorous predators that broke the mastodon's bones. Remains of other mammals have already been found at the site, although the most interesting are by far those of the mastodon, which include two tusks, 16 ribs, four vertebrae, and over 300 bone fragments.
A boulder discovered at the Cerutti Mastodon site thought to have been used by early humans as a hammerstone.
"At many sites you have evidence that bones were used for hammers or anvils", says Richard Fullagar, an archaeologist at Australia's University of Wollongong.
"To demonstrate such early occupation of the Americas requires the presence of unequivocal stone artifacts", says Michael Waters of Texas A&M University. Dr. Rob Benson, Adams State professor of geology and earth sciences, assisted Beeton by running X-Ray Diffraction on soil samples in the university's Interdisciplinary STEM Laboratory, and by collaborating on thin section analysis.
The new findings were published online today (April 26) in the journal Nature. He has also published articles in major worldwide peer-reviewed journals such as Geoarchaeology and Quaternary Research.