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A 130,000-year-old archaeological site in southern California, USA
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A 130,000-year-old archaeological site in southern California, USA
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Journal Article
A 130,000-year-old archaeological site in southern California, USA
2017
Overview
Evidence of mastodon bone modifications for marrow extraction and/or tool production, found in the presence of hammerstones and anvils that showed use-wear and impact marks, suggest the presence of
Homo
in North America around 130 thousand years ago.
America's oldest human activity
Around 130,000 years ago, a mastodon died near what is now San Diego, California. Although this seems uncontroversial, Thomas Deméré and colleagues present evidence that the carcass had been modified by human beings. Stone hammers and anvils were found alongside mammoth bones and teeth that show signs of having been broken by percussion, presumably to extract bone marrow. Dating the site has been problematic because the bones preserved too little collagen for radiocarbon dating, and optically stimulated luminescence dating put the age at over 60,000–70,000 years. Dates based on the decay of uranium, constrained by the movement of uranium between the environment and the bone, now give an age of around 130,000 years. If confirmed, this would extend tenfold the time that human beings are known to have been present in the Americas and predate the time that modern humans are thought to have first left Africa. The identity of the hominin species—if any—remains unknown.
The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context
1
,
2
. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where
in situ
hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (
Mammut americanum
). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum.
230
Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of
Homo
at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa
3
,
4
,
5
,
6
, Eurasia
7
,
8
,
9
and North America
10
,
11
,
12
. The CM site is, to our knowledge, the oldest
in situ
, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of
Homo
into the Americas.
