Cerutti Mastodon site
The Cerutti Mastodon site is a paleontological and possible archeological site located in San Diego County, California. In 2017, researchers announced that broken mastodon bones at the site had been dated to around 130,700 years ago.
The bones were found with cobblestones displaying use-wear and impact marks among the otherwise fine-grain sands. Researchers have proposed that these marks were caused by the intentional breakage of the broken bones by hominins using the cobblestones. If so, this suggestion would be older by far than the scientific consensus for habitation of the New World, which generally traces widespread human migration to the Americas to 13,000 to 16,000 years ago.
The Cerutti Mastodon site (SDNHM locality 3767) is a paleontological site located in San Diego County, California, United States. A team of researchers from the San Diego Natural History Museum, led by Thomas Deméré, excavated the site from 1992 to 1993. The site is named after Richard Cerutti, another paleontologist from the museum who is credited with discovering the site during freeway expansion of State Route 54.
The fossil remains of a juvenile male Mammut americanum (SDNHM 49926) were discovered in stratigraphic layer Bed E at the site: the recovered bones include 2 tusks, 3 molars, 4 vertebrae, 16 ribs, 2 phalanx bones, 2 sesamoids and over 300 other bone fragments. The remains of dire wolf, horse, camel, mammoth and ground sloth were also discovered at the site. Five cobbles displaying use-wear and impact marks were also recovered from the site in Bed E.
The research team found cobbles and broken mastodon bones lying together at the site. Uranium-thorium dating of bones from the site estimates a dating of around 130,700 (±9,400) years ago for the Cerutti Mastodon site. The research team claims that the cobbles found at the site were used as hammerstones and anvils. The research team also claims that the mastodon bones show signs of intentional breakage by hominins. If so, this would indicate that some form of Homo was present in the Americas at an extremely early age. 
The dating of the peopling of the Americas is a very contentious subject. For most of the 20th Century, the Clovis First theory was dominant, dating human habitation of the Americas to no earlier than 13,000 years ago. Later data pushed back the date from Clovis First, with theories suggest dates of approximately 15,000 to 24,000 years ago. Other theories proposed dates as early as 40,000 years ago.
Given the substantial differences between these theories and the Cerutti findings, some researchers responded with skepticism. Several critics have argued that the evidence from the site did not definitively rule out the possibility that the cobbles may have been altered due to natural causes. Other critics also cite the lack of lithic artifacts and debris, generally found at sites associated with lithic tool manufacturing, at the Cerutti Mastodon site. Archaeologists also cite the lack of taphonomic evidence at the site, evidence that is generally required to support claims of material culture.
No human bones were found, and the claims of tools and bone processing have been described as "not plausible". Michael R. Waters commented that "To demonstrate such early occupation of the Americas requires the presence of unequivocal stone artefacts. There are no unequivocal stone tools associated with the bones... this site is likely just an interesting paleontological locality." Chris Stringer said that "extraordinary claims require extraordinary evidence - each aspect requires the strongest scrutiny," adding that "High and concentrated forces must have been required to smash the thickest mastodon bones, and the low energy depositional environment seemingly provides no obvious alternative to humans using the heavy cobbles found with the bones."
Another 2017 paper by eight anthropologists including Tom Dillehay, David J. Meltzer, Richard Klein, Vance T. Holliday and Jon M. Erlandson pointed out the ample supply of good stone for making tools in the area, saying that "the absence of clearly modified chipped stone tools at the CML is damning". They argued that nothing has yet been found to prove that there were hominims in the Americas before ∼50 kya.
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