Increased ecological resource variability during a critical transition in hominin evolution

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Science Advances  21 Oct 2020:
Vol. 6, no. 43, eabc8975
DOI: 10.1126/sciadv.abc8975
  • Fig. 1 Archeological and faunal transitions in the Olorgesailie basin and location, lithology, and geochronology of the Olorgesailie Drilling Project core OLO12-1A.

    (A to C) Locations of Koora basin drill core, Olorgesailie, Lainyamok fossil site, and east-to-west faulted topography (cross section). (D) Olorgesailie basin Acheulean technology spanning ~1 Ma to 500 ka ago; replacement by Middle Stone Age technology ~320 ka ago; and turnover in the fossil mammalian fauna (68), including community-level change in body mass, water dependence, and feeding strategies (table S1). Fossil assemblages dated between ~397 and 300 ka ago recording the faunal turnover are from Olorgesailie and Lainyamok (7, 8, 43). The hominin behavioral and faunal transitions in the Olorgesailie basin occurred during an erosional hiatus dated ~500 to 320 ka old. (Map image: TanDEM-X DEM DLR; tool images: Smithsonian Institution.) (E) Koora basin drill core depth (meters below surface), lithological sequence, and age constraints spanning from ~1.084 Ma to ~83.5 ka ago, based on Bayesian age model (40Ar/39Ar ages ± 1σ and Brunhes/Matuyama magnetostratigraphic boundary*) (19). Shaded zone indicates drill core lithological record during the hiatus in the Olorgesailie outcrop record. See Fig. 2, fig. S1 (lithological key), and Materials and Methods.

  • Fig. 2 Stratigraphic and paleohydrologic relationships between the Koora basin, where the ODP-OLO12-1A drill core was obtained (Fig. 1), and the Olorgesailie basin, where the transitions in Acheulean-MSA behavior and mammalian fauna are recorded.

    (A) Correlation between OLO12-1A z-prime core stratigraphy and the Olorgesailie basin outcrop record, based on dates in (7, 8, 19). The core’s stratigraphic column is corrected for rapid and instantaneous deposits with thick volcanoclastic layers (red color) and event deposits removed. The overall z-prime core thickness is therefore lower than that of the recovered core; see (19). Outcrop Land color code: orange, aggrading sediment; brown, stable land surface; red, burned zone. (B) Hypothesized reconstruction of basin history and drainage relationships of the Olorgesailie and Koora basins from 500 ka ago to present. The sequential maps show the connections between the two basins, based on sediment correlations and tephra dates, and illustrate increasing compartmentalization of this part of the southern Kenya rift over the past 500 ka (34). This reconstruction conforms to the present-day topography; the spatial extent of the Koora basin paleolake is approximate. Question marks denote uncertainties in lake extent in the northern Koora basin. Color code: blue, lake; white, eroding outcrops of the Olorgesailie Fm.; red-orange, major paleosol (base of Olkesiteti Mb., Oltulelei Fm.); purple, major volcaniclastic influx (Olkesiteti Mb, Oltulelei Fm.); orange, volcaniclastics plus fluvial siliciclastic sediments (Oltepesi Mb., Oltulelei Fm.). Red dots in the Koora basin mark the locations of drill cores.

  • Fig. 3 Paleoenvironmental data from core ODP-OLO12-1A.

    Colored horizontal bars summarize intervals of similar paleoenvironmental conditions; darker to lighter colors represent lower to higher variability intervals. Vertical yellow bars denote paleosols (PSOLS), indicating lake desiccation. (A) Water availability data: XRD shows major mineral groups (zeolites: predominantly analcime and phillipsite). Correspondence analysis (CA) scores of diatom assemblage data indicate fluctuations in lake water depth. EC of paleolake waters are derived from a diatom transfer function (blue, fresh; green, brackish; red, saline; 2500 μS/cm assumed limit of potable water for humans). Ratio of silica and potassium counts from XRF analysis shows five-point moving average; high (low) values indicate high (low) diatom productivity (text S3) (88). (B) Vegetation dynamics data: Stable carbon isotope values of carbonate nodules (δ13Cpc) from paleosols; vegetation classes from (89). Tree cover density index (D/P) of phytolith assemblage data (30): higher values indicate dense woody cover; green dots denote absence of grass phytoliths. Stable isotope values of bulk sedimentary organic matter (δ13Corg; black) and proportion of C3 versus C4 plants from plant leaf wax isotopes (δ13Cwax; red). Phytolith index (Iph) from grass phytolith data indicate proportion of short (Chloridoideae) versus tall (Panicoideae) grasses (29). All datasets are plotted at their median age. Dots denote single data points; envelopes reflect 68% (dark) and 95% (light) confidence intervals (19). Continuity of data and uncertainty envelopes are interrupted at hiatuses, core gaps, and measurement gaps.

  • Fig. 4 Time-series (power spectrum) analyses on ODP-OLO12-1A environmental indicator (proxy) records.

    Lomb-Scargle spectra for (A) the diatom CA1 axis, an indicator for lake depth, (B) the XRF Si/K ratio, an indicator of paleohydrology, and (C) the phytolith D/P index, an indicator of paleovegetation and tree cover. Orbital periods (400, 100, 41, and 23 to 19 ka) are shown with red dashed lines. Spectral analysis was used to explore orbital variability within the various time series, taking into account the uncertainty of the age model (see Materials and Methods). Darker colors represent spectral powers of the data that are more consistent across the full age model. Orbital variability is present but subdued in these records: The percentage of total variance occurring at orbital periods is only 11% in the diatom CA1 record (8% eccentricity, 2% obliquity, and 1% precessional periods), 17% in the XRF Si/K time series (8% eccentricity, 7% obliquity, and 1% precessional periods), and 16% in the phytolith D/P tree cover record (9% eccentricity, 3% obliquity, and 4% precessional periods). Records are shown in comparison with orbital cycles in fig. S4.

  • Fig. 5 Transitions in resource dynamics, hominin behavior, and mammalian fauna over time based on the OLO12-1A drill core and Olorgesailie outcrop data.

    (A) Water availability and vegetation dynamics based on Fig. 3 datasets (see text). Darker bars reflect relatively consistent resources, lighter colors more variable resources. Intermediate-to-deep lake conditions ~938 to 830 ka ago are based on lower-resolution data due to core gaps (table S4). (B) Change in resource base availability and predictability based on the synthesis in (A). The horizontal bars in (A) and (B) describe dominant inferred patterns for each time period of the core; the transitions are not typically abrupt. (C) Major transitions in hominin behavior and the herbivore community based on outcrop records of the southern Kenya rift. These transitions took place during the erosional hiatus between 500 and 320 ka ago. The marked shift from reliable to variable resource landscapes beginning ~400 ka ago in the adjacent Koora record (fig. S9) occurred within the interval of the Olorgesailie erosional hiatus and the major transitions.

  • Table 1 Comparison of Acheulean technology [typified by handaxes and other large cutting tools (LCTs)] and MSA technology.

    Behavioral and environmental comparison includes lithic source access and rock transport, pigment use, and environment evidence based on observations in the Olorgesailie basin (68, 34), located 22 to 24 km from the OLO12-1A drilling site. Predicted insolation dynamics (high or low climate variability) based on (5).

    (Olorgesailie basin)
    Olorgesailie Fm.
    (1.2 Ma to 499 ka ago)
    lower Oltulelei Fm.
    (~320 to 295 ka ago)
    Artifact/tool sizeLarge tools, LCTs
    Smaller, diversified
    Focus of lithic source
    Local volcanic rocks,
    coarse, and fine-grain
    Fine-grain rocks (e.g.,
    obsidian, chert, and
    fine-grain local
    Stone transport
    No more than 5 kmObsidian transfer: 25
    to 95 km, from
    multiple directions
    Altered and used
    Depositional regime
    Stable, aggrading
    system (lake/fluvial/
    Highly dynamic
    landscape (sub-basin
    East Africa insolation
    Alternating high-low
    climate variability
    Sustained period of
    strong climate

Supplementary Materials

  • Supplementary Materials

    Increased ecological resource variability during a critical transition in hominin evolution

    Richard Potts, René Dommain, Jessica W. Moerman, Anna K. Behrensmeyer, Alan L. Deino, Simon Riedl, Emily J. Beverly, Erik T. Brown, Daniel Deocampo, Rahab Kinyanjui, Rachel Lupien, R. Bernhart Owen, Nathan Rabideaux, James M. Russell, Mona Stockhecke, Peter deMenocal, J. Tyler Faith, Yannick Garcin, Anders Noren, Jennifer J. Scott, David Western, Jordon Bright, Jennifer B. Clark, Andrew S. Cohen, C. Brehnin Keller, John King, Naomi E. Levin, Kristina Brady Shannon, Veronica Muiruri, Robin W. Renaut, Stephen M. Rucina, Kevin Uno

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    • Supplementary Materials and Methods
    • Figs. S1 to S9
    • Legends for tables S1 to S12
    • Texts S1 to S3
    • References

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