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A 130,000-year-old archaeological site in southern California, USA

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Abstract

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.

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Figure 1: Plan of the CM excavation site.
Figure 2: Percussion-modified bone specimens (illustrated by 3D surface models).
Figure 3: Cobble refits.
Figure 4: Diagnostic impact marks.

Change history

  • 08 May 2017

    An earlier version of Fig. 2a without a scale bar was incorrectly used in the HTML and PDF versions; this has been updated.

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Acknowledgements

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.

Author information

Affiliations

Authors

Contributions

R.A.C. discovered the CM site and led the excavation team. T.A.D. and S.R.H. conceived the study. S.R.H., T.A.D., K.A.H., R.A.C., D.C.F. and G.T.J. analysed the mastodon bone modifications. R.A.C., T.A.D., S.R.H., K.A.H. and D.C.F. identified refits of bones and cobbles. R.F. conducted the lithic use-wear analysis. J.M.B. and T.A.D. conducted the geological and soils analysis. J.B.P. conducted the U-series dating. D.C.F. provided mastodon skeletal identifications and analyses. G.T.J. and L.V. conducted the comparative taphonomic analysis. D.C.F. and A.N.R. produced the 3D models and videos of bone and cobbles. S.R.H., K.A.H. and R.F. conducted the experimental elephant, cow and kangaroo bone breakage. S.R.H., T.A.D., D.C.F., R.F., J.B.P., G.T.J., J.M.B. and K.A.H. wrote the paper with contributions by all other co-authors.

Corresponding authors

Correspondence to Steven R. Holen or Thomas A. Deméré.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks E. Hovers and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 The CM site.

a, Map of southwestern San Diego County, California, USA, showing the location of the CM site (red dot). Map created by E. Parrish using esri data and software. b, Stratigraphy of CM site: Bed D (C horizon; sandy loam; cross-bedded; fluvial), Bed E (Bk horizon; loam; fluvial) and Bed F (Bt horizon; loam; fluvial) as exposed in excavation grid unit G5. Contacts at Beds D–E and Beds E–F transitions are gradational. c, Total sand, silt and clay percentages from pipette analysis of 15 bulk samples collected in stratigraphic order showing a clear upward-fining sequence in 3 cm increments beginning in Bed D and continuing through Beds E and F. The clay percentage increases near the top of Bed F (Bt horizon) and Bed E (Bk horizon).

Extended Data Figure 2 Schematic representation of Mammut skeletal elements.

Most elements are shown in approximately lateral aspect, except for basihyoid (oblique), and manus and pes elements (most anterior, calcaneum dorsal). Coloured elements were sufficiently intact to determine their anatomical positions. Dark blue elements were determined with the greatest precision. Light blue elements were determined except for the side. Light green elements were determined with an uncertainty of ±2 positions within their respective series. Red elements were determined with an uncertainty of ±2 positions within their respective series, but the side was undetermined. Femoral diaphyses (red diagonal stripes) are the probable source of most cortical bone fragments showing conspicuous ‘green fractures’.

Extended Data Figure 3 Bones and cobbles exposed during excavation.

a, Oblique view of concentration 1 in grid unit E3. Note the position of anvil CM-281, spirally-fractured femoral fragments CM-288 and CM-292 and molar fragment CM-286. b, Plan view of in situ femoral heads in grid units D3/E3. c, Plan view of vertical tusk in grid unit B2, showing cross-section of concentric dentin layers exposed by backhoe. d, Plan view of in situ caudal vertebra and rib in grid units D4 and E4. e, Plan view of portion of in situ rib (left) and hammerstone CM-383 (right) in grid unit H4. Note the carbonate ‘rind’ on CM-383. f, Oblique view of in situ hammerstone CM-423 in grid unit G5. Note the fine-grained aspect of Bed E containing CM-423.

Extended Data Figure 4 Diagnostic anvil wear on CM bone.

ae, Spiral-fractured femur segment CM-288. a, V-shaped projection with anvil polish (rectangle). b, Side view with V-shaped projection. c, Outer, cortical surface. d, Side view with impact surface and bulb of percussion (highlighted with a black dashed line) on opposite side from anvil wear. e, Enlarged area from a showing impact fracture marks (arrows) where the bone rested on the anvil. f, Spiral-fractured V-shaped cortical bone CM-329 with anvil polish (oval). g. Spiral-fractured bone CM-255 that refits with CM-329 (white rectangle showing the location of the close-up shown in h). h, Enlarged area from g showing anvil striations. Scale bars, 2 cm (a), 5 cm (bd), 5 mm (e), 10 mm (fh).

Extended Data Figure 5 Percussion-caused features on molar and cobble specimens.

a, b, Molar impact flake CM-9. a, Bulb of percussion (arrow). b, Negative flake scar (arrow). c–e, Andesite flake CM-221. c, Ventral view showing slight edge rounding on the proximal internal platform edge (arrows). d, Oblique dorsal view showing proximal dorsal scars (arrows) with step terminations. e, Platform view showing natural cortical surface and step-terminated scars. f, i, Molar segment CM-286. f, Cross-sectional view showing impact area (rectangle, magnified in i). i, Close-up of the impact area showing flake scar (left arrow) and bulb of percussion (right arrow). g, Fragment CM-262 refitted on fragment CM-254 with both refitted on pegmatite hammerstone CM-423. These fragments were probably dislodged by a blow to the end of CM-423 (square). h, End-on view of CM-423, showing pitting and cracks from the impact. Note that caliche covers the pitted area adjacent to zones where caliche covers the cortex. jn, Andesite hammerstone CM-7 and impact flake CM-141 showing use-wear features. j, Upper surface of CM-7 showing refitted flake CM-141 (square, top) and a battered ridge (rectangle, bottom). k, Battered ridge on CM-7 (rectangle in j) with stone-on-stone impact scars (arrows) indicating the direction of blows. l, Detail of refitted flake CM-141 showing rounded external platform edge (left arrow) and older flake scar initiation (right arrow). m, Dorsal view of refitted flake CM-141 showing location and direction of impact (arrow) adjacent to fresh fracture scars of prior flake removals. n, Fresh fracture surface on andesite hammerstone CM-7 where flake CM-141 refits, showing fissures and cracks converging on the point of impact (arrow). Scale bars, 5 mm (ae, kn), 10 mm (f, i), 2 cm (g, h).

Extended Data Figure 6 Wear on experimental bone pounding tools.

ad, Elephant experiment. a, Eight-cm wide tip of the experimental cobble hammerstone showing pitted zone (ellipse, magnified in b). b, Detail of use-wear in a showing pitted zones (ellipse and circles). c, Detail of use-wear shown in circles in b. d, Detail of use-wear (striations) on an individual quartz grain in the lower right circle in c. ej, Cow experiment. e, Tip of the experimental granite cobble hammerstone showing pitted zone (square). f, Naturally weathered cortex of cobble shown in e away from any contact with bone. g, Detail of pitted area (in ellipses) on the experimental cobble in e showing angular quartz crystals, depressions/pits where crystals have been dislodged and white powdery cobble debris. h, Tip of argillite hammerstone showing pitted zones and fractures (square). i, Detail of striations (white arrows) and the impact fractures (black arrows) shown in h. j, Detail of striations (arrows pointing upward) above crushing and a step scar (arrow pointing downward). km, Kangaroo experiment. k, Granite cobble hammerstone showing impact and pitted zone (square, magnified in l). l, Detail of pitted zone from k. m, Striations (arrows) and abrasive smoothing/polish (flat whiter zones near striations) associated with pitted zones shown in l. Bone residues appear as lightly translucent white tissue (ellipses). Scale bars, 2 cm (a, e, h, k), 10 mm (b, i, j), 2 mm (c), 1 mm (f, g), 5 mm (l), 500 μm (d), 100 μm (m).

Extended Data Figure 7 Pleistocene land mammal excavation grid maps and stratigraphic profile of in situ tusk.

a, Partial horse skeleton (SDNHM 47731) recovered in Bed D. b, Partial dire wolf (SDNHM 49012) and deer excavation (SDNHM 49666) recovered in Bed D. Deer bones confined to grid units H8 and H9. c, Profile of vertically oriented mastodon tusk CM-56 recovered from grid unit B2. Note that the tusk extends from the level of Bed E into underlying Beds D and C through a caliche layer. Note the infilling of sediment from Bed D along the leading margin of the embedded tusk.

Extended Data Figure 8 Experimental hammerstone percussion of elephant bone.

a, Breakage of elephant femur in Tanzania (photograph provided by C. Musiba). b, Breakage of elephant femur in Colorado, USA. Note the spirally fractured bone fragment in mid-air near the right knee of the person holding the hammerstone (photograph provided by K. Alexander). c, Femur in a broken at mid-shaft. Smooth spiral fractures characteristic of green-bone breakage, attached cone flake (top left arrow) and broad arcuate percussion notch (bottom right arrow) (photograph provided by C. Musiba). d, Detached cone flakes produced by hammerstone on Colorado elephant femur. Arrows show cortical platforms and adjacent bulbs of percussion. e, Illustration showing radiating spiral fractures and impact point surrounded by cone flakes produced by hammerstone impact. f, Cross-section showing cone flakes formed around the impact point.

Extended Data Figure 9 Experimentally produced anvil wear.

a, b, Elephant femur broken on the cobble anvil by hammerstone percussion. a, Femur segment with refitting bone flakes. b, Close-up (square in a) of anvil polish on high points (short arrows) and striations (long arrows) (photograph provided by E. Duke). c, d, Cow femur broken on the cobble anvil by hammerstone percussion. c, Femur segment with refitted bone flake. Scale bar, 1 cm. d, Close-up (square in c) of anvil polish and striations (arrows) (photograph provided by E. Duke). eg, CM bones used for radiometric analysis. Bone segments (CM-20, CM-225 and CM-292) and corresponding cross-sections subsampled for U-series dating profiles. Numbered red areas were subsampled by sequential micro-milling.

Extended Data Figure 10 Results of U-series isotope analyses.

See also Supplementary Table 12. a, Relative U concentrations and conventional 230Th/U ages for profiles across three sections of cortical bone from samples CM-20 (n = 13), CM-225 (n = 14) and CM-292 (n = 30) plotted against relative distance from the midpoint of each section. b, U-series isotope-evolution plot showing measured activity ratios and error ellipses representing 2× s.d. (2σ), compositional paths for material with initial 234U/238U activity ratios of 1.4, 1.5 and 1.6 (dark curved lines), and isochrons labelled in ka. c, Results from diffusion–adsorption–decay (DAD) modelling of CM bone profiles using iDAD algorithms30. Left plots represent the marginal probability density function (blue curve) with maximum likelihood model age (thick vertical lines) and 95% credible interval half widths (thin vertical lines). Middle and right plots show individual 234U/238U and 230Th/238U activity ratios and maximum likelihood solutions for iDAD models (dashed lines). d, Best estimate of burial age of 130.7 ka (solid horizontal line) and 2σ uncertainties (±9.4 ka; dashed lines) determined as the mean of DAD dates for profiles shown in c weighted by their respective uncertainties.

Supplementary information

Supplementary Information

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. (PDF 1752 kb)

Animation of a 3D surface model of CM-222 (also illustrated in Fig. 2c), an “impact flake” made on cortical bone of Mammut

View using Windows Media Player (select “Repeat” to loop video, showing scale bar at end of each cycle; remove cursor from frame to close progress bar and maximize viewing area) or by dragging file onto an open tab in Chrome (after video starts, right-click within frame, uncheck “Show controls” option and check “Loop” option to watch several cycles). Upper panel of animation shows model with vertex-color; lower panel shows a mostly grayscale model that displays topography more clearly. Color overlay on grayscale model: yellow, impact surface; red, convex ovoidal surface (bulb of percussion; dark color proximal to point of impact; light color distal to point of impact); blue, concave ovoidal surface (negative bulb of percussion; dark color proximal to point of impact; light color distal to point of impact); dotted blue line, margin of hinge fracture at periphery of negative bulb. Symmetry axis of ovoidal impactor indicates trajectory of impact responsible for flake. See caption of Fig. 2 for additional annotation. Animation starts with ventral view of flake, rotates to dorsal view showing a negative flake scar and hinge fracture, continues to a slightly elevated lateral view showing topography of both sides of flake and angle of impactor, tilts to look down on hinge fracture, rotates to look down axis of impactor, and then ends looking straight down on the impact surface. This type of flake is clearly produced by percussion. (MP4 3155 kb)

Animation of a 3D surface model of CM-230 (also illustrated in Fig. 2b), a cone-flake made on cortical bone of Mammut

See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Additional annotation in caption of Fig. 2. Pause in animation offers a low-angle view along the ventral fracture surface, showing the convex curvature of a subtle bulb of percussion (red) just below the (yellow) impact surface (no impactor shown with this model, but trajectory of impact would have been normal to impact surface). This type of flake is clearly produced by percussion. (MP4 2874 kb)

Animation of a 3D surface model of CM-288 (also illustrated in Extended Data Fig. 4a-e), a spiral-fractured piece of cortical bone from one of the Mammut femora

See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation shows a simple rotation of the models. The grayscale version is portrayed with an abstract impactor and anvil, both of which rotate with the bone fragment. The form of this fragment is characteristic of green-bone fracturing. (MP4 1658 kb)

Animation of a 3D surface model of CM-340 (also illustrated in Fig. 2d), a large fragment of femoral cortical bone of Mammut

See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation begins with a simple rotation of the fragment, then zooms in to the area of impact, where two concentric negative (concave) flake scars (light blue patches) bracket a partial, undetached flake, before elevating to show the impact notch on the outer cortical surface (yellow) just above the undetached flake. No impactor is shown with this model, to avoid obscuring detail, but trajectory of impact would have been normal to impact surface. The form of this fragment and impact notch are characteristic of percussion-induced green-bone fracturing. (MP4 7508 kb)

Animation of a 3D surface model of CM-438a (also illustrated in Fig. 2a), a cone-flake made on cortical bone of Mammut

See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation starts with a view of the ventral surface, rotates 360º, passing the dorsal surface, then continuing in an upward arc to look down on the cortical (impact) surface, then reversing to return to the starting point. No impactor is shown with this model, but trajectory of impact would have been normal to impact surface. This type of flake is clearly produced by percussion. (MP4 4230 kb)

Animation of 3D surface models of CM-255, 263a, 263b, 329 and 390, fragments of thick cortical bone (probably femoral) of Mammut

See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Animation shows a 360º rotation of the entire assembly of bone fragments, then shifts to a more elevated perspective for a second 360º rotation. During this second turn, the fragments fly apart and then together again to show how they fit precisely to reconstruct the larger assembly. (MP4 5862 kb)

Animation of 3D surface models of CM-109, 254, 262, 283, 284, 304 and 423, fragments of a pegmatite hammerstone shown in the map in Fig. 3 (CM-423 is also shown in Extended Data Figs. 3f and 5g,h).

See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Animation begins by rotating about 180º near the equatorial plane of the oblate spheroid this assembly resembles, then rises to look down on this plane. During the next 180º rotation, the fragments fly apart and then together again to show how they fit precisely to reconstruct the original, unbroken cobble. (MP4 12153 kb)

Video record of experimental breakage of elephant limb bone in Tanzania and later experiments in Colorado, USA.

Multiple impacts with a hafted hammerstone succeed in breaking a femur across a proximal portion of the diaphysis. Later, an unhafted hammerstone is used to remove flakes from the cortical wall of a transversely fractured bone. Replicated green-bone fractures show properties comparable to those of specimens from the Cerutti Mastodon site. (MP4 11219 kb)

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Holen, S., Deméré, T., Fisher, D. et al. A 130,000-year-old archaeological site in southern California, USA. Nature 544, 479–483 (2017). https://doi.org/10.1038/nature22065

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