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 context1,2. 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. 230Th/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 Africa3,4,5,6, Eurasia7,8,9 and North America10,11,12. 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.
The following individuals worked at the CM site: L. Agenbroad (deceased), B. Agenbroad, J. Mead, M. Cerutti, M. Colbert, C. P. Majors, B. Riney, D. Swanson (deceased) and S. Walsh (deceased). M. Hager was instrumental in ensuring completion of this project. J. Berrian and D. Van der Weele photographed bone and rock specimens and K. Johnson (SDNHM), S. Donohue (SDNHM), C. Abraczinskas (UMMP) and E. Parrish produced various main and Extended Data Figures. E. Hayes, J. Field and V. Rots assisted with photography and interpretation of use-wear on cobbles. C. Musiba and K. Alexander provided photographs of the experimental elephant bone breakage. E. Duke provided the photographs of the experimental anvil wear on bone. Financial support was provided by Caltrans-District 11, P. Boyce and D. Fritsch, The James Hervey Johnson Charitable Educational Trust, The National Geographic Society (Research Grant 4971-93), The Walton Family Foundation (at the recommendation of J. and C. Walton) and the many donors to the Center for American Paleolithic Research. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.
Extended data figures
This file contains a discussion of the Geological and Depositional Setting of the Cerutti Mastodon site, Sediment Analysis for the site, Usewear and Impact Marks on CM Hammerstones and Anvils, Proboscidean Taphonomy (natural vs. cultural modification of limb bones), Experimental Breakage of Elephant (and other animal) Limb Bone, Taphonomy of Skeletal Remains, Radiocarbon and Optically Stimulated Luminescence Dating, Uranium-series Ages and Asian Origins of Early Humans on the West Coast of North America. Collectively, this material supports our interpretation of the Cerutti Mastodon site.