Museum paleontologists work at the Cerutti Mastodon site in San Diego in 1993.
Using stone hammers and anvils similar to those found, they broke open large elephant bones much in the way pre-historic humans might have done.
Since its initial discovery, the Cerutti Mastodon site has been the subject of research by top scientists to date the fossils accurately and evaluate microscopic damage on bones and rocks that authors now consider indicative of human activity.
Twenty-four years ago, construction workers building a new highway near San Diego stumbled upon a skeleton that may rewrite the entire history of the Americas.
The researchers found evidence that 130,000-year-old bones and teeth of a mastodon at the side were modified by early humans.
Until recently, archaeologists acknowledged that the oldest documented human sites in North America are about 14,000 years old.
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During their press conference on Tuesday, they invited other researchers to examine the evidence, some of which will be on display at the San Diego Natural History Museum next week. "Since the original discovery, dating technology has advanced to enable us to confirm with further certainty that early humans were here much earlier than commonly accepted".
"The bones and several teeth show clear signs of having been deliberately broken by humans with manual dexterity and experiential knowledge", stated Dr Holen. It could not have been the work of carnivorous predators that broke the mastodon's bones. "The suggestion is that this site is strictly for breaking bone", said Deméré, "to produce blank material, raw material to make bone tools or to extract marrow".
Stone tools from the Cerutti Mastodon site: (a-d) anvil; (a) upper surface; boxes indicate images magnified in b-d; dashed rectangle, magnified in b, small dashed square, magnified in c and solid square, magnified in d; (b) cortex removal and impact marks (arrows); (c) striations (arrows) on the highest upper cortical surface ridge; (d) striations (diagonal arrows) and impact marks with step terminations characteristic of hammer blows (vertical arrows). "This establishes the geologic context and helps my colleagues tell the paleontological and, in this case, the archaeological story of the site". "This, Holen [and his colleagues] have most certainly not done, making this a very easy claim to dismiss". They were in Siberia around 50,000 years ago. Judy Gradwohl, president and chief executive officer of the San Diego Natural History Museum. 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 "real mystery" is how the report was published in the scientific journal" Nature," he added.
Author and site excavator Thomas Deméré, a paleontologist at the San Diego Natural History Museum, says the team carefully excavated 50 square meters beginning in 1992, and the bones described in the paper were "deeply buried". He has also published articles in major worldwide peer-reviewed journals such as Geoarchaeology and Quaternary Research.
This Jan. 25, 1993 photo provided by the San Diego Natural History Museum shows a concentration of fossil bone and rock at an excavation site in San Diego, Calif.
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