Stable carbon isotopes from paleosol carbonate and herbivore enamel document differing paleovegetation signals in the eastern African Plio-Pleistocene

Accepted Manuscript Stable carbon isotopes from paleosol carbonate and herbivore enamel document differing paleovegetation signals in the eastern African Plio-Pleistocene

Andrew Du, Joshua R. Robinson, John Rowan, Ignacio A. Lazagabaster, Anna K. Behrensmeyer PII: DOI: Reference:

S0034-6667(18)30123-4 https://doi.org/10.1016/j.revpalbo.2018.11.003 PALBO 4021

To appear in:

Review of Palaeobotany and Palynology

Received date: Revised date: Accepted date:

1 June 2018 31 October 2018 1 November 2018

Please cite this article as: Andrew Du, Joshua R. Robinson, John Rowan, Ignacio A. Lazagabaster, Anna K. Behrensmeyer , Stable carbon isotopes from paleosol carbonate and herbivore enamel document differing paleovegetation signals in the eastern African Plio-Pleistocene. Palbo (2018), https://doi.org/10.1016/j.revpalbo.2018.11.003

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ACCEPTED MANUSCRIPT Stable carbon isotopes from paleosol carbonate and herbivore enamel document differing paleovegetation signals in the eastern African Plio-Pleistocene

Andrew Du1* , Joshua R. Robinson2* , John Rowan3,4 , Ignacio A. Lazagabaster3 , Anna K.

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637,

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Behrensmeyer5

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U.S.A.

Department of Anthropology, University of South Carolina, Columbia, SC 29208, U.S.A.

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Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University,

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Tempe, AZ 85282, U.S.A.

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Department of Anthropology, University of Massachusetts Amherst, Amherst, MA 01003, U.S.A.

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Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington,

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DC 20013, U.S.A.

*These authors contributed equally to this work Corresponding authors: (AD) [email protected] and (JRR) [email protected]

Keywords: paleosol carbonates; herbivore enamel; stable isotopes; paleovegetation; PlioPleistocene; hominin evolution

ACCEPTED MANUSCRIPT Abstract Analyses of stable carbon isotopes (δ13 C) from herbivore dental enamel and paleosol carbonates are important tools for Plio-Pleistocene paleovegetation reconstructions. A single herbivore tooth documents an isotopic record of vegetation on the order of 10-1-1 years and in proportion to that

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individual’s foraging range. Paleosol carbonates, conversely, record environmental information

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on longer time scales (102-3 years) but smaller spatial scales (101 m2 ). Given that these two

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proxies document paleoenvironments at different spatiotemporal scales, it is worth comparing them to see if they offer redundant or complementary paleovegetation information. Here, we

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compare δ13 C patterns from herbivore enamel and paleosol carbonates from geological

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(sub)members in the Awash Valley, Ethiopia, and Turkana Basin, Kenya, from ~ 4.4 – 1 million years ago. We find that median herbivore enamel δ 13 C is typically ~ 5-7 per mil (‰) higher than

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that from paleosol carbonates within a given (sub)member. The distributions of paleosol

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carbonate δ13 C values usually have less spread (variation) than herbivore enamel. The bias in median and spread between these two data types likely reflects the different spatial and temporal

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scales at which these proxies record paleoenvironmental information. Most Plio-Pleistocene

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fossiliferous deposits are formed in fluvial settings in which paleosol carbonates sample the immediate habitat of floodplain woodlands and shrubs, resulting in a lower δ 13 C (i.e., more C 3 )

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signal. On the other hand, fossil teeth of wide-ranging herbivores could generate a higher (i.e., more C4 ) and more variable δ 13 C signal if some taxa fed in floodplain woodlands while others fed on open grasslands distal to the floodplain. We conclude that δ13 C values from herbivore enamel and paleosol carbonates offer paleovegetation data at different spatiotemporal scales, both of which are informative for hominin habitat reconstructions. Careful consideration of the

ACCEPTED MANUSCRIPT spatial and temporal signals inherent in these and other proxies should be applied in future

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studies.

ACCEPTED MANUSCRIPT 1. Introduction Stable carbon isotope (δ 13 C) analyses have become one of paleoecology’s most powerful tools for reconstructing the paleovegetation context of Plio-Pleistocene human evolution in eastern Africa (e.g., Cerling et al., 2011, 2015; Levin et al., 2008; Levin, 2015; Robinson et al.,

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2017; Sponheimer et al., 2013; Wynn et al., 2013, 2016). Such studies are grounded in the fact

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that in tropical regions, including eastern Africa, δ 13 C ratios are reliable indicators of the C3 and

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C4 photosynthetic pathways used by different plant groups. The distinct carbon isotope distributions of C3 (trees and shrubs) and C4 (grasses) plants are recorded in the tissues of

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primary consumers, such as mammalian herbivores (e.g., antelopes, elephants, rhinos, pigs), and

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in surrounding soils and therefore can be used to infer the dietary ecologies of fossil species and the vegetation of ancient landscapes (Figure 1). Stable carbon isotopic analyses of herbivore

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dental tissues (i.e., enamel; δ 13 C[enamel]) and carbonates from ancient soils (i.e., paleosols; δ 13 C[pc])

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are the two most common proxies for reconstructing the paleovegetational context of human evolution. Paleodiet has routinely been interpreted from the carbon isotopic profile of the tooth

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enamel of African herbivore communities. Paleovegetation is inferred from dietary information

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based on the assumption that a species’ diet is linked to the physical and ecological characteristics of the habitats it occupies (e.g., Cerling et al., 1997, 2003, 2015; Harris et al.,

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2008; Kingston and Harrison, 2007; Lee-Thorp, 1989; Levin et al., 2008, 2015; Sponheimer and Lee-Thorp, 1999a, 1999b; Sponheimer et al., 2003, 2013; White et al., 2009; Wynn et al., 2013, 2016). Community-based approaches (i.e., pooling δ13 C[enamel] data from multiple herbivore taxa) are often used in an effort to mitigate the effects of seasonality, migration, and taxon-specific physiology on the link between diet and environment (Caswell et al., 1973; Behrensmeyer and Hook, 1992). Similarly, δ 13 C[pc] values have been used to infer the proportions of C 3 and C4 plant

ACCEPTED MANUSCRIPT biomass on the paleolandscape (Cerling and Quade, 1993; Wynn, 2000, 2004; Levin et al., 2004; Behrensmeyer et al., 2007; Aronson et al., 2008; Cerling et al., 2011; Feakins et al., 2013; Levin, 2015). Collectively, these data are used to study the habitats hominin species occupied and the potential environmental selective pressures that shaped the course of human anatomical (e.g.,

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postcranial adaptations to bipedalism) and cultural (e.g., stone tool technologies) evolution.

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In eastern Africa, it is often possible to collect isotopic data from herbivore enamel and

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paleosol carbonates from a single locality (e.g., for the Hadar Formation, see Aronson et al., 2008 and Wynn et al., 2016), although usually not from the same sedimentary units because

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well-preserved fossils in paleosols are less common than they are in other types of fluvial and

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lacustrine deposits (Behrensmeyer and Hook, 1992). Appropriately combining paleovegetation evidence from these two proxies relies on precise knowledge of the spatial and temporal

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attributes of each data source. While differences in the spatial and temporal scales of enamel and

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paleosol carbonate δ13 C datasets have long been acknowledged (e.g., Koch et al., 1992; Kingston, 2007; Levin, 2015), less consideration has been given to probing the implications of

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this issue for paleovegetation reconstruction.

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The structure of our paper is as follows: 1) First, we review how herbivore enamel and paleosol carbonates each record δ 13 C

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information from paleovegetation. 2) Second, we briefly discuss how herbivore enamel and paleosol carbonates record paleovegetation information at different spatial and temporal scales. Scale incongruity might confound comparisons between the two proxies and result in different paleovegetation reconstructions, although to our knowledge a comprehensive analysis comparing the two has not been presented previously.

ACCEPTED MANUSCRIPT 3) Next, we empirically compare herbivore enamel and paleosol carbonate δ 13 C distributions (i.e., their medians and interquartile ranges) as recorded in PlioPleistocene localities in eastern Africa. 4) Finally, we examine our results in the context of scale and discuss how the two

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of the ancient environments that hominins inhabited.

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proxies are complementary, with each illuminating a different spatiotemporal aspect

1.1 Review of stable carbon isotopic analyses

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Plant δ13 C data —Plants that use the C 3 photosynthetic pathway (primarily trees, shrubs,

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and high-altitude grasses above 2000 m in present-day tropical ecosystems) have a range in δ 13 C values of -36 ‰ to -22 ‰ with a mean of -27.4 ± 2.0 ‰ in tropical Africa. In water-stressed 13

C-enriched with a mean δ 13 C value of -24.6 ± 1.1 ‰ (Tiezsen et al.,

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conditions, C3 biomass is

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1979, 1983; O’Leary 1981, 1988; Ambrose and DeNiro, 1986; Cerling et al., 2003; Sponheimer et al., 2003; Passey et al., 2005; Kohn, 2010). The large range in δ 13 C values for C 3 vegetation is

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due to variability in water availability, light, and temperature, as well as photosynthetic recycling

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of respired CO 2 in closed-canopy forests, known as the “canopy effect” (van der Merwe and Medina, 1991; Kohn, 2010). C 4 grasses (low-elevation tropical grasses) in Africa have a mean

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δ13 C value of -12.7 ± 1.2 ‰ with a range of -14 ‰ to -11 ‰ (Heaton, 1999; Harris and Cerling, 2002; Passey and Cerling, 2002; Cerling et al., 2003). Arid-adapted grasses are characterized by the NAD-me and PEP-ck C4 -subpathways (Hattersley, 1992; Chapman, 1996) and have an average δ 13 C value of -13.0 ± 0.7 ‰ (Cerling et al., 2003, 2015). C 4 grasses in mesic environments are characterized by the NADP pathway with an average δ 13 C value of -11.8 ± 0.2 ‰ (Cerling et al., 2003, 2015). Crassulacean Acid Metabolism (CAM) pathway plants,

ACCEPTED MANUSCRIPT predominantly succulents in dry environments and epiphytes in closed forests, have δ 13 C values between those of C 3 and C4 plants (O’Leary, 1981, 1988; Heaton, 1999) but are often not explicitly considered in stable isotope studies because: 1) they are not considered to have comprised a significant component of herbivore diets in Africa during the Plio-Pleistocene (e.g.,

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Cerling et al., 2003; Kingston, 2011; Garrett et al., 2015), and 2) they are not abundant in

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paleosol carbonate-forming settings (Quade and Levin, 2013). Carbon isotope composition is

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reported in δ notation, where δ 13 C = [(Rsample/Rstandard) – 1], R = 13 C/12 C, and δ is expressed in parts per thousand (‰ or “per mil”).

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Herbivore enamel δ13 C data—δ13 C[enamel] studies primarily focus on the carbonate

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fraction of bioapatite, which is known to be minimally affected by diagenesis and can therefore be analyzed to infer ancient diet (DeNiro and Epstein, 1978; Wang and Cerling, 1994; Cerling

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and Harris 1999; Sponheimer and Lee-Thorp, 1999a; Lee-Thorp, 2002; although see Kohn et al.,

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1999 and Zazzo, 2014). δ 13 C signatures of herbivore tooth enamel are a reflection of the isotopic composition of vegetation consumed, but are modified through diet-tissue fractionation (Tiezsen

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et al., 1983; Ambrose and DeNiro, 1986; Cerling and Harris 1999; Cerling et al., 2003;

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Sponheimer et al., 2003). The enrichment factor between diet and tooth enamel (where enrichment between enamel and diet, ε enamel-diet, is calculated from the fractionation factor, a, as

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εenamel-diet = [aenamel-diet – 1] x 1000 ‰) for large-bodied African herbivores is +13 – 15 ‰ (Cerling and Harris, 1999; Passey et al., 2005) with variation due to physiological and metabolic differences in food and nutrient processing (Tejada-Lara et al., 2018). Because diet-enamel fractionation values are strongly dependent on body size (Tejada-Lara et al., 2018), small-bodied herbivores, such as rabbits and voles, have values outside of the large-bodied herbivore range (Passey et al., 2005; Tejada-Lara et al., 2018). Additionally, the diet-enamel fractionation factor

ACCEPTED MANUSCRIPT for primates and hominins is not well known (Levin et al., 2015). We choose the middle value of 14 ‰ as our diet-enamel fractionation factor for all species in this study, which are composed of large-bodied herbivores and primates. In essence, the fractionation factor means that the isotopic signature of a tooth is 14 ‰ greater than that of its consumed plant matter.

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Paleosol carbonate δ13 C data—Soil organic matter preserves the in vivo CO2 signal of

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the overlying vegetation because it is supplied to the soil through the decay of the above and

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below ground components of plants. Soil carbonates that precipitate at depths 30 cm below the surface are formed in soil zones beyond the penetration of atmospheric CO 2 and are therefore

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formed in isotopic equilibrium with the surrounding soil (which includes organic matter),

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reflecting the isotopic composition of surface vegetation (Cerling, 1991; Koch et al., 1992; Cerling et al., 2011). Soil CO 2 , and therefore soil carbonate CO 2 , is enriched in

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C by 4.4 ‰

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relative to plant-derived CO 2 due to kinetic fractionation during diffusion of CO 2 from the soil to

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the atmosphere (Cerling, 1991; Cerling and Quade, 1993). Equilibrium fractionation during the precipitation of calcite will result in the enrichment of soil carbonates in

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C by 9.8 – 12.4 ‰

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C-enriched by a factor of +14 to +17 ‰ in comparison to overlying vegetation and

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are

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relative to soil CO 2 (Deines et al., 1974). As such, soil carbonates found 30 cm below the surface

unaltered soil organic matter (Cerling, 1991, 1992; Cerling et al., 1997; Quade and Levin, 2013).

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This is similar to the fractionation factor for African herbivores, thereby enabling direct comparisons between the δ 13 C values derived from enamel and paleosol carbonates. Variation in the paleosol carbonate enrichment factor may be the result of changes in the concentration of atmospheric CO 2 (Koch et al., 1992), though atmospheric CO 2 levels during the Plio-Pleistocene do not appear to have changed sufficiently (Pearson and Palmer, 2000; Wynn, 2004) for that to be a consideration in this study.

ACCEPTED MANUSCRIPT Spatiotemporal scale differences between the two proxies– The δ13 C composition of a single herbivore tooth provides a record of environment, as indirectly inferred from herbivore diet, on the order of months or years (based on the species) during tooth mineralization and in proportion to that individual’s foraging range during this period (DeNiro and Epstein, 1978;

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Passey and Cerling, 2002). A single paleosol carbonate nodule, on the other hand, records an

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isotopic signal over a limited area (~ 10 m2 ) averaged over hundreds or thousands of years

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(Cerling, 1991; Quade and Levin, 2013). Therefore, the temporal and spatial scales of one proxy are roughly the inverse of the other: δ13 C[enamel] values represent extremely short temporal

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intervals and potentially large spatial areas in the case of herbivores that forage over tens of

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square kilometers, while the opposite is true of δ13 C[pc].

The (time) averaging inherent in a paleosol carbonate nodule is different from the

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(spatial) averaging represented by a single herbivore tooth. For example, if vegetation patterns

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are changing through time, a paleosol carbonate nodule will cumulatively record and average those shifting vegetation dynamics over the duration of its formation (Behrensmeyer et al., 2007;

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Quade and Levin, 2013). On the other hand, if an herbivore is a dedicated browser or grazer (as

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is common in eastern Africa today, but not so in the past [Cerling et al., 2015]), it would only average δ 13 C values across a narrow range because of its specialized diet. The only taxa capable

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of spatially averaging δ 13 C values across a wide range of vegetation types would be mixed feeders (i.e., species that consume both browse and graze). As a result, a single herbivore might not necessarily spatially average different vegetation types across a paleolandscape, and individual teeth may offer a spatially high-resolution portrayal of what kind of vegetation was on the landscape, especially when analyzing the teeth of dietary specialists. To generate meaningful sample sizes, however, one would need to aggregate teeth from multiple generations or spatial

ACCEPTED MANUSCRIPT locations, thereby creating an emergent, spatially and temporally averaged paleovegetation signal. Given the different ways that paleosol carbonates and herbivore enamel average paleovegetation information, these two proxies may lead to different paleoenvironmental

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reconstructions, further complicated by the fact that paleosols and fossils usually do not occur in

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the same lithological units (at least in the eastern African record). Fossils are often found in

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aggrading alluvial, deltaic, or lake margin depositional facies, whereas paleosols represent temporarily stable land surfaces associated with floodplain or lake margin environments

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(Behrensmeyer, 1982; Kingston, 2007; Garrett et al., 2015; Levin, 2015). Despite these issues,

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enamel and paleosol carbonate δ 13 C data can be complementary because they record different spatial and temporal aspects of a paleoenvironment, as long as depositional biases are accounted

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for.

1.2 Goals of this paper

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The preceding section makes clear that paleovegetation reconstructions using δ13 C data

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from paleosol carbonates and herbivore enamel may potentially disagree due to the different spatiotemporal scales at which these proxies record paleoenvironmental information. Here, we

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test the degree to which paleovegetation reconstructions using paleosol carbonate data correspond to those derived from herbivore enamel in the Plio-Pleistocene record of eastern Africa from ~ 4.4-1 million years ago (Ma). We specifically focus on the extensive δ 13 C datasets from the highly fossiliferous Awash Valley, northeastern Ethiopia, and the Turkana Basin of northern Kenya (Table 1; Figure 2), both of which have produced substantial evidence for PlioPleistocene human evolution (e.g., Johanson et al., 1982; Kimbel et al., 2004; White et al., 2006,

ACCEPTED MANUSCRIPT 2009; Wood and Leakey, 2011; Villmoare et al., 2015). For paleosol carbonate and enamel isotope data from the same locality, we predict that if paleosol carbonates record a more (time) averaged environmental signal relative to herbivore enamel, then the spread of isotope values for the former should be smaller than the latter. This is because the tail values of a distribution are

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effectively “discarded” when an average is calculated (as is happening when a paleosol

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carbonate nodule is forming over time and averaging multiple habitats), so a collection of mean

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values (i.e., a sample of δ 13 C[pc]) should have a smaller range relative to that of the original data points (i.e., minimally averaged herbivore teeth, which record high-resolution habitat

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information). Furthermore, since paleosol carbonates (+14 – 17 ‰) and non-primate herbivore

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enamel (~ +14 ‰) have roughly the same degree of isotopic enrichment between vegetation and δ13 C values (Cerling, 1991, 1992; Cerling et al., 1997; Cerling and Quade, 1993; Cerling and

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Harris, 1999; Passey et al., 2005; Quade and Levin, 2013), we predict that the central tendencies

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of the two proxies should be nearly identical if they are sampling the same ecological conditions. If there is an offset, it should be primarily due to differences in the biochemical processes of

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fractionation, and we would expect it to be close to 1-2 ‰ (Koch et al., 1992).

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Accurate enamel isotopic characterization of the herbivore community (and presumably the inferred paleovegetation landscape) relies on random sampling of teeth from the original

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living community (i.e., the abundance of each isotopically sampled taxon must be proportional to that taxon’s abundance in the living community). Otherwise, δ13 C[enamel] values may be biased, and discrepancies between isotope signatures in enamel and paleosol carbonates may be caused by non-random sampling in the former. Here, we assume fidelity of abundances between the fossil and original living communities (Western and Behrensmeyer, 2009) and also that taphonomic spatial mixing of fauna from different habitats is minimal relative to their foraging

ACCEPTED MANUSCRIPT range (Behrensmeyer and Rogers, 2017). We use taxon abundances from published collection databases as a “benchmark” to which abundances of isotopically sampled taxa are compared. While there is a well-known collection bias towards primates and carnivores (Alemseged, 2007; Fleagle, 2002), our method assumes that even with these biases, abundances from faunal

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databases are more accurate representations of taxon abundances in the original living

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community than isotopically sampled abundances. We use the collection abundances to “correct”

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for non-random isotopic sampling of enamel and then compare our abundance-corrected enamel

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values to the δ13 C[pc] values.

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2. Materials and Methods 2.1 Data collation and standardization

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To be included in our analyses, fossil localities must have δ13 C data from herbivore

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enamel and paleosol carbonates and faunal abundance data (for “correcting” non-random isotopic sampling of enamel). This data criterion led to the exclusion of some prominent eastern

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African sites (e.g., Kanapoi).

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We compiled a database of published δ 13 C[enamel] data from fossil localities in the Awash Valley, Ethiopia, and Turkana Basin, Kenya, from 4.4-1 Ma (Table 1; Supplemental Dataset 1).

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δ13 C[pc] data used here come from Levin’s (2013; 2015) compilation as well as additional Nachukui Formation data from Quinn et al. (2013) and Harmand et al. (2015), both of which are not in the Levin database (Supplemental Dataset 1). We call our operational unit of analysis the “space-time unit” (STU), which we define as a geological member (or sometimes sub-member) for a given fossil locality (see Table 1 for the amount of time and order of magnitude of space represented by each STU). For example, the Denen Dora Member of the Hadar Formation at

ACCEPTED MANUSCRIPT Hadar, Ethiopia, is a STU for our purposes, as are the KBS and Okote members of the Koobi Fora Formation in East Turkana (Table 1; Figure 2). Faunal collection abundances were compiled from published sources for Aramis (White et al., 2009), the Hadar Geoinformatics Database for the Hadar Formation

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(http://gis1.asurite.ad.asu.edu/hadarv3/), and the Turkana Basin Database for the Turkana Basin

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(Bobe, 2011; http://www.mnh.si.edu/ete/ETE_Datasets_Turkana.html) (Supplemental Dataset

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2). All fossils assigned a unique database/accession number were included in abundance counts, and multiple parts unequivocally belonging to a single fossil individual (denoted by accession

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number letter modifiers) were counted as one individual (e.g., portions of “Lucy” [A.L. 288-1a,

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A.L. 288-1b, A.L. 288-1c…] were aggregated into a single individual, A.L. 288-1). The only exception to our protocol are the Australopithecus specimens from the A.L. 333 locality at Hadar

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(the “First Family”), for which every individual fragment is given a unique identification number

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in the database (amounting to a total of 281 specimens from A.L. 333). To avoid greatly overestimating the number of Australopithecus individuals for A.L. 333, we use a count of n=13

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for this locality following Robinson et al. (2017).

2.2 Analytical methods

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To determine how representative the distribution of isotopically sampled teeth is with respect to taxon abundances from collection databases, we calculated and compared taxon relative abundances from these two data sources. To calculate each STU’s relative abundances of taxa sampled for δ13 C[enamel], we simply divided each taxon’s number of individuals sampled for δ13 C[enamel] by the total number of individuals sampled for δ 13 C[enamel] summed across taxa for that STU. To calculate each STU’s taxon relative abundances from collection databases, we first

ACCEPTED MANUSCRIPT subset out which taxa were sampled for δ13 C[enamel]. Within this subset, we divided each taxon’s number of individuals by the total number of individuals summed across taxa for that STU. We created bar plots of binned δ13 C values to compare paleosol carbonate and herbivore enamel proxies for each STU. Bin width was set at 1 ‰, excluding values that fell on the left bin

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edge and including those that fell on the right. Counts of paleosol carbonate values in each bin

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were simply plotted as relative frequencies (i.e., counts within each bin were divided by the total

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count summed across bins). Enamel data were standardized following Robinson et al. (2017) to account for the possibility that taxa were not sampled for δ 13 C[enamel] in proportion to their

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observed abundances on the paleolandscape (as determined from collection abundance

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databases). This standardization method implicitly assumes that the δ13 C[enamel] values for sampled individuals within a taxon are representative of the diet for that entire taxon in a given

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STU. Initially focusing on one taxon, the method first creates a table by counting how many

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δ13 C[enamel] values fall within each 1 ‰ bin. These counts are then standardized by dividing each bin’s count by the total count summed across all bins. The relative δ 13 C[enamel] frequencies are

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then multiplied by the taxon’s relative abundance as calculated from collection databases for that

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given STU. This is repeated for all taxa with δ 13 C[enamel] data. The result is that δ 13 C[enamel] counts are standardized so that a taxon’s relative isotope δ 13 C[enamel] frequencies summed across all bins

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match that taxon’s relative abundance, calculated from collection databases. We elected not to plot the remaining total relative abundance deficit (i.e., abundances of unsampled taxa divided by total abundance of all taxa, as determined from collection databases) as error bars, as was done in Robinson et al. (2017), and instead simply inform the reader of the summed relative abundance as a measure of how complete enamel sampling coverage is across all taxa. Because we were concerned with the overall shape of the distribution and not how relative frequencies

ACCEPTED MANUSCRIPT were divided among taxa (as in Robinson et al., 2017), we summed all relative frequencies within each δ 13 C[enamel] bin for our bar plots. We then compared the central tendency and spread of paleosol carbonate and enamel δ13 C distributions for each STU using medians and interquartile ranges (IQR), which are

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appropriate given the non-normal shape of many of the distributions. For the paleosol carbonate

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data, these were calculated using the raw δ 13 C[pc] values. For δ13 C[enamel] values, however, we

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again standardized the data but moved away from the methodology of Robinson et al. (2017), which discretizes continuous data via binning and thus discards information. We instead

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calculated weighted medians and IQR standardized by collection abundance data. We weighted

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the δ 13 C[enamel] data so that the sum of weights for a given taxon’s δ13 C[enamel] values equals its relative abundance from collection databases (e.g., if Giraffa has a collections relative abundance

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of 0.24 and three δ13 C[enamel] measurements, the weight for each of those measurements would be

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0.08). We then used the weights and the weighted.median() and weighted.quantile() functions in the R package spatstat (Baddeley et al., 2015) to calculate weighted medians and weighted 1st

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and 3rd quartiles, the difference of which is IQR.

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Eleven of our sixteen analyzed STUs have an δ 13 C[enamel] sample size larger than that for δ13 C[pc]. If each STU’s δ13 C[enamel] IQR is larger than its δ13 C[pc] IQR as we predicted (see Section

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1.2), this could be parsimoniously explained by enamel’s greater sample size since more observations imply the tails of a distribution are better sampled (which results in larger IQR). To address this possibility, we subsampled each STU’s enamel data without replacement down to the observed sample size of that STU’s paleosol data for those eleven STUs that have more enamel samples than analyzed paleosol carbonates. The probability of sampling δ13 C[enamel] values was weighted using the weighting scheme in the previous paragraph. We then calculated

ACCEPTED MANUSCRIPT IQR for each vector of subsampled δ13 C[enamel] values and repeated this procedure 1,000 times. To obtain p-values, we calculated the proportion of each STU’s 1,000 subsampled enamel IQRs that was less than or equal to the observed paleosol IQR. If observed paleosol IQR is significantly lower than the distribution of subsampled enamel IQR, this would indicate the spread of δ13 C[pc]

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account. R code for this analysis is provided in Supplemental File 1.

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values is smaller than that of δ13 C[enamel] even when sample size differences are taken into

3. Results

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3.1 Comparing taxon relative abundances between collection databases and δ13 C[enamel]

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samples

Relative abundances of isotopically sampled taxa generally do not correspond well with

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taxon relative abundances calculated from collection datasets (Figure 3; Supplemental Dataset

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3). For those few STUs where there is some agreement between the two proxies (e.g., Sidi Hakoma, Denen Dora; Figure 3), there is still notable scatter. For example, the highest point on

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the Sidi Hakoma plot (Figure 3), Theropithecus, has a collection relative abundance of 0.12 but

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an isotope relative abundance of 0.17; this amounts to a difference of about 40% (i.e., [0.17 – 0.12] / 0.12). Generally speaking, as the collection relative abundance rises above 0.1, taxa tend

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to be undersampled for δ13 C[enamel]. The relative abundance discrepancy between these two sources highlights the need to standardize the number of isotopically sampled individuals using abundance information from collection databases (Robinson et al., 2017), or to sample taxa for δ13 C[enamel] values in proportion to their collection abundances. Furthermore, there are also differences between STUs in the degree of taxonomic coverage of the δ 13 C[enamel] samples (Table

ACCEPTED MANUSCRIPT 2). While most of the identified taxa have been sampled for δ13 C[enamel] at the Aramis and Hadar STUs, Turkana Basin STUs exhibit great variability in the degree of taxonomic coverage.

3.2 Comparing δ13 C values from herbivore enamel and paleosol carbonates

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For all STUs considered here, except for Aramis (~ 4.4 Ma) and Lokochot (~ 3.5 Ma),

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standardized bar plots of δ13 C[enamel] values (gray bars in Figure 4) peak at higher values,

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indicating diets predominantly of C4 foods, and have tails at lower δ 13 C[enamel] values, representative of C3 diets. Aramis and Lokochot have long tails towards higher δ 13 C[enamel] values

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with peaks at lower δ 13 C[enamel] values. These patterns are not mirrored in their respective paleosol

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carbonate data (black bars in Figure 4), which are unimodal with less spread and lower degrees of skew.

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Perhaps the most noticeable difference between the distributions of δ 13 C[enamel] and

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δ13 C[pc] values is the clear offset between their medians of about 5-7 ‰ (Figures 4 and 5a), contrary to our initial predictions. This can be seen clearly in Figure 5a, where the weighted

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median of δ13 C[enamel] values is always more positive than the median value of δ13 C[pc] (except for

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Aramis and Lokochot). Despite this offset, once the outliers of Aramis and Lokochot are excluded, there is a linear relationship between the median δ13 C values of the two proxies

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(Figure 5a), suggesting that even though absolute δ 13 C values differ, relative differences are maintained (r = 0.72).

Another major difference between these two datasets is the degree of spread in the δ13 C data, as measured by IQR. In agreement with our prediction, the IQR of δ13 C[enamel] values is greater than that of δ13 C[pc] values (except for the upper Lomekwi/Lokalalei and Nariokotome STUs from the Nachukui Formation) (Figure 5b), though there is an unexpected negative

ACCEPTED MANUSCRIPT relationship between the two measures (r = -0.49 across all STUs). As mentioned previously, however, the IQR of a distribution is correlated with sample size, and these patterns could be the result of larger sample sizes of δ13 C[enamel] measurements relative to those from paleosol carbonates. Indeed, in all but five STUs (Koobi Fora Formation: Lokochot and Tulu Bor

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members; Nachukui Formation: Kataboi, Kalochoro, and Kaitio members), δ13 C[enamel] datasets

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have a larger sample size than δ13 C[pc] datasets (Figure 5c). Our analyses show that even after

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accounting for sample size, the majority of each STU’s δ13 C[enamel] subsampled iterations have larger IQR than their observed δ13 C[pc] IQR, except for Nariokotome (Figure 6). For the five

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STUs that had more δ 13 C[pc] than δ 13 C[enamel] samples, the observed paleosol carbonate IQR was

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still less than that calculated from δ13 C[enamel] values, which is the opposite result expected based on sample size arguments. Seven of the STUs, including Aramis, Hadar Formation members Sidi

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Hakoma and Kada Hadar, Koobi Fora Formation members KBS and Okote, and Nachukui

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Formation members lower/middle Lomekwi and upper Lomekwi/Lokalalei, have δ13 C[pc] IQR significantly below δ 13 C[enamel] IQR (p < 0.05, one-tailed test). In addition, the Denen Dora

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Member of the Hadar Formation (p = 0.07) has close to significantly lower IQR for δ 13 C[pc]

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values. Again, only the Nariokotome Member of the Nachukui Formation appears to have an

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IQR that is smaller for δ13 C[enamel] than for δ13 C[pc].

4. Discussion

Kingston (2007) argued that linking hominin evolution with environmental change falls short due to the lack of a conceptual framework for combining datasets of varying spatiotemporal scales, and he advocated for an explicitly hierarchical framework that incorporates such scales (see also Feibel, 1999; Behrensmeyer, 2006; Levin, 2015). Here, we

ACCEPTED MANUSCRIPT have attempted to shed new light on this problem by comparing two commonly used δ13 C proxies (i.e., herbivore enamel and paleosol carbonates) in a scale-explicit theoretical framework that we expand upon below. Summarizing our results, we find that median δ 13 C[enamel] values are usually enriched 5-7 ‰ relative to median δ13 C[pc] values, more than the 1-2 ‰ expected if the

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difference is due to biochemical aspects of fractionation (Koch et al., 1992), and that δ13 C[pc] IQR

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is smaller than δ13 C[enamel] IQR even when sample size effects are accounted for. We suggest

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these differences are due to enamel and paleosol carbonate δ 13 C datasets providing differently scaled information about paleovegetation, and we hypothesize which properties of past habitats

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these two proxies record and how these records can be used complementarily.

4.1 Developing a scale-explicit theoretical framework to explain the observed δ13 C[enamel]

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and δ13 C[pc] patterns

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Most of the STUs we analyzed were deposited in fluvial or fluvio-deltaic systems (Campisano and Feibel, 2007, 2008; Feibel, 2011), which exhibit a general pattern of vegetation

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structure in which gallery forests or woodlands occur immediately adjacent to the channel (i.e.,

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on levees and proximal floodplains), as well as across the more extensive floodplain of the channel belt. Because herbivores are mobile and wide-ranging, individuals could feed on either

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the immediate C3 resources in the floodplain woodland, C4 grasses on the distal floodplain or adjacent upland areas, or a combination of both. It is also likely that most herbivores would move off the floodplains into surrounding areas during seasonal flooding cycles and feed on vegetation adapted to conditions drier (e.g., C4 grasses) than those on river floodplains or lake margin habitats, where the water table is usually closer to the ground surface and more stable than areas farther from the river channel.

ACCEPTED MANUSCRIPT Most vertebrate body fossils, however, would be buried and preserved in river channels of various scales (either in situ or as transported remains) or in actively aggrading floodplain deposits including fine-grained channel fills (Behrensmeyer, 1988; Behrensmeyer and Hook, 1992). If the floodplain landscape was stable for an extended period of time (e.g., 102-3 years),

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under suitable geochemical and hydrological conditions, a carbonate-producing soil would form.

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Over longer periods that make up the STUs, basin subsidence would lead to successive deposits

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of fluvial, deltaic, or lake margin environments (including paleosols) being buried and preserved, generating STUs with preserved vertebrate fossils and paleosol carbonates from the same broad

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ecosystem. In cases where the overall depositional environment remained the same (e.g., fluvial),

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paleosol carbonates could record a primarily C3 signal of floodplain woodlands (and shrubs), though there is still some C 4 signal in the paleosol carbonate data (Figure 4), indicating the

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presence of limited or perhaps seasonal grasslands on the floodplain. Herbivore individuals, on

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the other hand, would collectively exhibit a more C4 signal because they sample the fuller spectrum of vegetation available to them on the broader paleolandscape (also suggested by Levin

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et al., 2008). This scenario would explain both the median δ 13 C offset between the two proxies

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and the smaller IQR in paleosol carbonates (because they are mainly capturing the woodland

herbivores).

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signal of a floodplain, which is part of the larger mosaic landscape inhabited by the mammalian

If a paleosol carbonate nodule represents a more time-averaged paleovegetation signal compared to a single herbivore tooth, this would further decrease the spread of δ 13 C[pc] values given that averaging removes the tails of a distribution. This could explain why even though the majority of analyzed STUs have a higher median δ 13 C[enamel] value than δ13 C[pc], most of these STUs still have δ 13 C[enamel] values lower than the lowest δ13 C[pc] value (e.g., all of the Hadar STUs

ACCEPTED MANUSCRIPT and many of the Turkana STUs; Figure 4). Addressing a related problem, Levin and colleagues (2004) proposed that paleosol carbonates in fluvial settings might not exhibit endmember C 3 values because the formation time of a carbonate nodule exceeds the residence time of a channel. That is, a channel and its riparian woodlands will have migrated away leaving grasses in its

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place, causing paleosol carbonate nodules to average C 3 and C4 signals together (see also Figure

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8b in Behrensmeyer et al., 2007).

4.2 A potential test of our theoretical framework

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One way to test our fluvial hypothesis regarding the difference s between a STU’s

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δ13 C[enamel] and δ 13 C[pc] values would be to collect these data for a STU that has no major paleochannels or fluvial context (and therefore no floodplain woodlands). One candidate is the

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upper Member 1 paleosol at Olorgesailie, Kenya, which is exposed laterally over 4 km of

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outcrop (Sikes et al., 1999). Sikes and colleagues (1999) analyzed 61 paleosol carbonate nodules and found δ13 C[pc] values ranged from -1.8 to 3.0 ‰ (mean = 1.1 ‰), which translates to a local

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biomass of 75-100% C4 plants. Though there are fossils preserved in this paleosol (Potts et al.,

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1999), none have been sampled for δ 13 C isotopes. We predict, however, that the median enamel δ13 C should be roughly the same as that from the paleosol carbonates unless foragers ranged into

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habitats with trees or other C 3 resources outside the preserved outcrop area. Uplifted fault blocks and Mt. Olorgesailie, which are within a few kilometers of the outcrop areas, would likely have supported more C 3 vegetation, as they do today. In this case, the median δ 13 C for enamel would be lower than that for paleosol carbonates, which is opposite the pattern we see in our analyses. In fact, this phenomenon may explain why Aramis and Lokochot show median δ 13 C offsets but in the opposite direction seen at the other STUs (Figures 4 and 5a), because these were deposited

ACCEPTED MANUSCRIPT at some distance from a major river channel (Woldegabriel et al., 2009; Feibel, 2011). We would expect the spread of δ 13 C[enamel] from the Olorgesailie Member 1 paleosol to be greater than that of δ13 C[pc] if there is enough paleovegetation variation across the paleolandscape (e.g., due to the presence of trees away from the carbonate sampling sites). The greater degree of time-averaging

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in paleosol carbonates relative to enamel would also cause the spread of δ 13 C[pc] to be relatively

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smaller.

4.3 Potential confounding factors in our δ13 C[enamel] and δ13 C[pc] comparison results

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Some of the raw δ 13 C[pc] data points in our analyzed dataset are averages (as determined

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from the original Levin [2013] database), which might explain why δ13 C[pc] IQR is lower than δ13 C[enamel] IQR for most STUs. Each averaged δ13 C[pc] value is calculated across multiple

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samples (range: 2-4) derived from either a single carbonate nodule or from multiple nodules

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within one meter of lateral exposure (Levin, 2013). Therefore, we would not expect each set of raw δ13 C[pc] values to vary much (in fact, the median coefficient of variation for each of these

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averaged values is only 0.05). Moreover, the averaged δ 13 C[pc] values only constitute 12% of all

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δ13 C[pc] data points, and seven STUs do not have any averaged values. Within each of the remaining STUs, averages make up 3% to 100% of data points (median = 30%; Figure 7).

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Because each one of these averaged δ 13 C[pc] values is accompanied by a standard deviation and number of samples (Levin, 2013), we can definitively assess whether this bias affects our IQR comparisons by simulating raw δ 13 C[pc] values for each averaged value as a random draw from a normal distribution with the provided mean, standard deviation, and sample size. Iterating this 1,000 times, we find δ 13 C[pc] IQR values are the same, regardless of whether we include the

ACCEPTED MANUSCRIPT averaged values or simulate raw ones (R2 = 0.79 when using the 1:1 line as the linear model; Figure 7). There remains the possibility that within STUs, fossils and paleosol carbonates might not have been sampled from the same area and time period (e.g., fossils are from the lower Okote

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Member, whereas paleosol carbonates are from the upper part). We could not assess this due to

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the absence of associated fine-scale spatiotemporal information within STUs in the published

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datasets. However, even if we assume an extreme form of this bias where fossils and paleosol carbonates come from completely different areas and time periods, we have no a priori reason to

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expect the median difference between δ 13 C[enamel] and δ 13 C[pc] to be of the same magnitude and in

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the same direction in 14 out of 16 STUs (i.e., it is unlikely that fossils happen to sample the more C4 area and time period within a STU 14 out of 16 times). The likelihood of getting such a result

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(or more extreme) by chance is exceptionally low (p = 0.002; one-tailed exact binomial test), so

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there must be a larger-scale, more consistent biasing factor operating across STUs, related to how these two proxies record δ13 C data (i.e., our proposed fluvial hypothesis). The same

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argument holds for the IQR results given how general they are across STUs.

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The formation of carbonate nodules in paleosols requires a negative water budget, such that the C3 endmember of vegetation immediately proximate to a paleochannel might not be

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recorded (Quade and Levin, 2013). This makes it all the more remarkable that most STUs show δ13 C[pc] medians 5-7 ‰ less than those from δ13 C[enamel]. The negative water budget bias might contribute to the smaller spread in δ13 C[pc] values, but the bias is probably not sufficient to account for the entirety of IQR differences between δ 13 C[enamel] and δ 13 C[pc]: δ13 C[enamel] IQR is at least 40% greater than δ 13 C[pc] IQR in 10 out of the 16 STUs analyzed and is at least twice as great in 7 STUs. Thus, an extraordinarily large portion (≥ 40%) of the plant δ13 C spectrum must

ACCEPTED MANUSCRIPT not be preserved by paleosol carbonates, if the negative water budget bias was to fully explain the observed IQR differences between δ 13 C[enamel] and δ 13 C[pc]. We view this as unlikely, so there must be additional processes acting to decrease the IQR of δ 13 C[pc] (i.e., δ13 C[pc] only recording proximate floodplain woodland habitats, and time-averaging of paleovegetation signals in

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δ13 C[pc]).

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4.4 Implications for the reconstruction of Plio-Pleistocene hominin habitats Because it is important to match the scale of one’s research question to the scale of

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empirical evidence at hand, the ability of enamel and paleosol carbonates to record

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paleovegetation patterns at different spatiotemporal scales can be viewed as a strength and not a shortcoming. For example, if one is interested in high temporal resolution, spatial questions in

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hominin evolution (e.g., hominin landscape use), the aim should be to collect teeth across space

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along a single marker bed, though the configuration of exposed outcrops may not permit such a collection strategy. Or if it does and adequate sample sizes cannot be achieved, some pooling of

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different fossil horizons is necessary. On the other hand, if one is interested in long-term

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evolutionary trends in hominin morphology, establishing a time series of δ13 C[pc] data would be an ideal approach, since the time-averaged nature of paleosol carbonate nodules should smooth

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out short-term environmental noise that is not relevant to the research question (though the small spatial scale of recorded paleovegetation information must be kept in mind). Depending on the question at hand, data from each proxy can be used to fill in spatial or temporal gaps in the other, or to examine short term spatiotemporal variation within longer term trends to create more complete, nuanced reconstructions of paleovegetation change in hominin habitats.

ACCEPTED MANUSCRIPT 5. Conclusions The analysis of both enamel and paleosol carbonate δ 13 C data has become increasingly common in Plio-Pleistocene paleovegetation reconstructions. Yet, using these proxies to determine the relationship between hominins and paleovegetation is complicated by the fact that

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they record paleoenvironmental data on different spatiotemporal scales. Our analyses indicate

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that paleosol carbonate data at the scale of our STUs in the Turkana and Awash basins

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consistently have less spread in δ13 C values than herbivore enamel data from the same units, even when sample size effects are accounted for, and that median enamel δ 13 C is typically ~5-7

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‰ greater than paleosol carbonate δ 13 C. We hypothesize these differences are due to the fluvial

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depositional environments of most Plio-Pleistocene sites: paleosol carbonates record a more C 3 signal from floodplain woodlands and shrubs, while large mammal taxa feed on these C 3

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resources as well as C 4 ones farther from the channel belt. Greater degrees of time-averaging

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involved in the formation of paleosol carbonate nodules may also contribute to the smaller spread in their δ13 C values compared to those from herbivore enamel. Careful consideration of

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the spatial and temporal signals inherent in these and other proxies should be applied in future

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studies. With a greater scale-explicit understanding of what these two proxies and others (e.g., Reed, 2008; Uno et al., 2016a, 2016b; Ungar et al., 2017) tell us about paleovegetation, we can

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leverage this information to more effectively advance our understanding of the role of environmental change in the evolution of the hominin clade in eastern Africa.

Acknowledgments Thanks to Enqu Negash for discussions about enamel and paleosol carbonate isotope data. We also thank Jonathan Wynn for discussions about his faunal abundance isotope normalization

ACCEPTED MANUSCRIPT method. Dominique Garello kindly provided the map shown in Figure 2. Rhonda Quinn provided previously unpublished raw paleosol carbonate data from the Nachukui Formation. We thank David Patterson for reading an earlier draft of this work, and comments from two anonymous reviewers greatly improved the manuscript. JR was supported by a National Science Foundation

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Graduate Research Fellowship. IAL was partially supported by a “la Caixa” Foundation

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Graduate Fellowship. We thank the decades of researchers who have provided isotope data used

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in this paper and Naomi Levin in particular for her publicly available compilations of eastern

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African paleosol isotope data.

ACCEPTED MANUSCRIPT References Alemseged, Z., Bobe, R., Geraads, D. 2007. Comparability of fossil data and its significance for the interpretation of hominin environments. In: Bobe, R., Alemseged, Z., Behrensme yer, A. (Eds.) Hominin environments in the East African Pliocene: An assessment of the

IP

T

faunal evidence Springer, Dordrecht, pp. 159-181.

CR

Ambrose, S.H., DeNiro, M., 1986. Reconstruction of African human diet using bone collagen

US

carbon and nitrogen isotope ratios. Nature, 319, 321–324.

AN

Aronson, J.L., Hailemichael, M. and Savin, S.M., 2008. Hominid environments at Hadar from

M

paleosol studies in a framework of Ethiopian climate change. J Hum Evol, 55, 532-550.

ED

Baddeley, A., Rubak, E., Turner, R., 2015. Spatial Point Patterns: Methodology and Applications

PT

with R. Chapman and Hall/CRC Press, London.

AC

211-227.

CE

Behrensmeyer, A.K., 1982. Time resolution in fluvial vertebrate assemblages. Paleobiology, 8,

Behrensmeyer, A.K., 1988. Vertebrate preservation in fluvial channels. Palaeogeogr Palaeoclimatol Palaeoecol, 63, 183-199.

Behrensmeyer, A.K., 2006. Climate change and human evolution. Science, 311, 476-478.

ACCEPTED MANUSCRIPT Behrensmeyer, A.K., Hook, R., 1992. Paleoenvironmental contexts and taphonomic modes. In: Behrensmeyer, A.K., Damuth, J., DiMichele, W., Potts, R., Sues, J., Wing, S. (Eds.). Terrestrial Ecosystems Through Time: Evolutionary Paleoecology of Terrestrial Plants and Animals.

T

University of Chicago Press, Chicago, 15-136.

IP

Behrensmeyer, A.K., Quade, J., Cerling, T.E., Kappelman, J., Khan, I.A., Copeland, P., Roe, L.,

CR

Hicks, J., Stubblefield, P., Willis, B.J. and Latorre, C., 2007. The structure and rate of late Miocene expansion of C 4 plants: Evidence from lateral variation in stable isotopes in paleosols of

AN

US

the Siwalik Group, northern Pakistan. Geol Soc Am Bull, 119, 1486-1505.

Behrensmeyer, A.K., Rogers, R.R., 2017. The tyranny of transport in taphonomy – how far do

M

bones really move and how much does it matter? Journal of Vertebrate Paleontology, Program

ED

and Abstracts, 2017, 79-80.

CE

Anthropol, 20, 254-263.

PT

Bobe, R., 2011. Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin. Evol

AC

Breecker, D.O., Sharp, Z.D., McFadden, L.D., 2009. Seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central New Mexico, USA. Geological Society of America Bulletin, 121, 630-640.

ACCEPTED MANUSCRIPT Campisano, C.J. and Feibel, C.S., 2007. Connecting local environmental sequences to global climate patterns: evidence from the hominin-bearing Hadar Formation, Ethiopia. J Hum Evol, 53, 515-527.

T

Campisano, C.J. and Feibel, C.S., 2008. Depositional environments and stratigraphic summary

IP

of the Pliocene Hadar formation at Hadar, Afar depression, Ethiopia. The geology of early

CR

humans in the Horn of Africa, 446, 179-201.

AN

herbivory: a hypothesis. Am Natur, 107, 465-480.

US

Caswell, H., Reed, R., Stephenson, S., Werner, P., 1973. Photosynthetic pathways and selective

ED

paleosols. Am J Sci, 291, 377-400.

M

Cerling, T.E., 1991. Carbon dioxide in the atmosphere: evidence from Cenozoic and Mesozoic

PT

Cerling, T.E., 1992. Use of carbon isotopes in paleosols as an indicator of the P(CO2) of the

CE

paleoatmosphere. Global Biogeochemical Cycles, 6, 307-314.

AC

Cerling, T.E. and Quade, J., 1993. Stable carbon and oxygen isotopes in soil carbonates. Climate change in continental isotopic records, 217-231.

Cerling, T.E., Harris, J., 1999. Carbon isotope fractionation between diet and bioapatite in ungulate mammals and implications for ecological and paleoecological studies, Oecologia. 120, 347–363.

ACCEPTED MANUSCRIPT Cerling, T.E., Harris, J.M., Ambrose, S.H., Leakey, M.G. and Solounias, N., 1997. Dietary and environmental reconstruction with stable isotope analyses of herbivore tooth enamel from the Miocene locality of Fort Ternan, Kenya. J Hum Evol, 33, 635-650.

T

Cerling, T.E., Harris, J., Passey, B.H., 2003. Diets of East African Bovidae based on stable

CR

IP

isotope analysis. J Mammal, 84, 456–470.

Cerling, T.E., Wynn, J.G., Andanje, S.A., Bird, M.I., Korir, D.K., Levin, N.E., Mace, W.,

US

Macharia, A.N., Quade, J. and Remien, C.H., 2011. Woody cover and hominin environments in

AN

the past 6 million years. Nature, 476, 51-56.

M

Cerling, T.E., Andanje, S.A., Blumenthal, S.A., Brown, F.H., Chritz, K.L., Harris, J.M., Hart, J.,

ED

Kirera, F., Kaleme, P., Leakey, L., Meave, L., Levin, N.E., Manthi, F., Passey, B.H, and Uno, K.T., 2015. Dietary changes of large herbivores in the Turkana Basin, Kenya from 4 to 1

CE

PT

Ma. Proc Natl Acad Sci USA, 112, 11467-11472.

AC

Chapman, G.P., 1996. The biology of grasses. Cab International.

Deines, P., Langmuir, D., Harmon, R.S., 1974. Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate groundwaters. Geo Cosm Acta, 38, 1147-1154.

DeNiro, M.J., Epstein, S., 1978. Influence of diet on the distribution of carbon isotopes in animals. Geo Cosm Acta, 42, 495-506.

ACCEPTED MANUSCRIPT Feakins, S.J., Levin, N.E., Liddy, H.M., Sieracki, A., Eglinton, T.I. and Bonnefille, R., 2013. Northeast African vegetation change over 12 my. Geology, 41, 295-298. Feibel, C.S., 1999. Tephrostratigraphy and geological context in paleoanthropology. Evol

T

Anthropol, 8, 87-100.

CR

IP

Feibel, C.S., 2011. A geological history of the Turkana Basin. Evol Anthropol, 20, 206-216.

US

Fleagle, J.G., 2002. The primate fossil record. Evo Anthropol, 11, 20-23.

AN

Garrett, N.D., Fox, D.L., McNulty, K.P., Faith, J.T., Peppe, D.J., Van Plantinga, A., Tryon, C.A., 2015. Stable isotope paleoecology of Late Pleistocene Middle Stone Age humans from the Lake

ED

M

Victoria basin, Kenya. J Hum Evol, 82, 1-14.

Harmand, S., Lewis, J.E., Feibel, C.S., Lepre, C.J., Prat, S., Lenoble, A., Boës, X., Quinn, R.L.,

PT

Brenet, M., Arroyo, A., Taylor, N., 2015. 3.3-million-year-old stone tools from Lomekwi

CE

3, West Turkana, Kenya. Nature, 521, 310.

AC

Harris, J. Cerling, T.E., 2002. Dietary adaptations of extant and Neogene African suids. J Zool, 256, 45-54.

Harris, J., Cerling, T.E., Leakey, M., Passey, B.H., 2008. Stable isotope ecology of fossil hippopotamids from the Lake Turkana Basin of East Africa. J Zool, 275, 323-331.

ACCEPTED MANUSCRIPT Hattersley, P., 1992. C 4 photosynthetic pathway variation in grasses (Poaceae): its significance for arid and semi-arid lands. In: Chapman, G. (Ed). Desertified Grasslands: Their Biology and Management. Linnean Society, London, pp. 181–212.

C/12 C Ratios of C3Plants:

IP

CR

Implications for Palaeodiet Studies. J Archaeol Sci, 26, 637-649.

13

T

Heaton, T., 1999. Spatial, Species, and Temporal Variations in the

Johanson, D.C., Taieb, M., Coppens, Y., 1982. Pliocene hominids from the Hadar Formation,

US

Ethiopia (1973-1977): stratigraphic, chronologic, and paleoenvironmental contexts, with notes

AN

on hominid morphology and systematics. Am J Phys Anthropol, 57, 373-402.

M

Kimbel, W.H., Rak, Y. and Johanson, D.C., 2004. The skull of Australopithecus afarensis.

ED

Oxford University Press.

PT

Kingston, J.D., 2007. Shifting adaptive landscapes: Progress and challenges in reconstructing

CE

early hominid environments. Yearb Phys Anthropol, 134, 20-58.

AC

Kingston, J.D., 2011. Stable isotopic analyses of Laetoli fossil herbivores. In: Harrison, T. (Ed.). Paleontology and geology of Laetoli: Human evolution in context. Springer, Netherlands, pp. 293-328. Kingston, J.D., Harrison, T., 2007. Isotopic dietary reconstructions of Pliocene herbivores at Laetoli: Implications for early hominin evolution. Palaeogeogr Palaeoclimatol Palaeoecol, 243, 272-306.

ACCEPTED MANUSCRIPT

Koch, P.L., Zachos, J.C. and Gingerich, P.D., 1992. Correlation between isotope records in marine and continental carbon reservoirs near the Palaeocene/Eocene boundary. Nature, 358,

T

319-322.

IP

Kohn, M., 2010. Carbon isotope compositions of terrestrial C 3 plants as indicators of (paleo)

CR

ecology and (paleo) climate. Proc Natl Acad Sci USA, 107, 19691-19695.

US

Kohn, M.J., Schoeninger, M.J. and Barker, W.W., 1999. Altered states: effects of diagenesis on

AN

fossil tooth chemistry. Geo Cosm Acta, 63, 2737-2747.

M

Lee-Thorp, J.A., 1989. Stable carbon isotopes in Deep Time: The diets of fossil fauna and

ED

hominids. Ph.D. Dissertation. University of Cape Town, Cape Town.

PT

Lee-Thorp, J.A., 2002. Two decades of progress towards understanding fossilization processes

CE

and isotopic signals in calcified tissue minerals. Archaeometry, 44, 435-446.

AC

Lee-Thorp, J.A., Sponheimer, M., 2003. Three case studies used to reassess the reliability of fossil bone and enamel isotope signals for paleodietary studies. Journal of Anthropological Archaeology, 22, 208-216.

Levin, N.E., 2013. Compilation of East Africa Soil Carbonate Stable Isotope Data. https://doi.org/10.1594/IEDA/100231.

ACCEPTED MANUSCRIPT

Levin, N.E., 2015. Environment and Climate of Early Human Evolution. Annu Rev Earth Planet Sci, 43, 405-429.

T

Levin, N.E., Quade, J., Simpson, S.W., Semaw, S. and Rogers, M., 2004. Isotopic evidence for

CR

IP

Plio-Pleistocene environmental change at Gona, Ethiopia. Earth Plant Sci Lett, 219, 93- 110.

Levin, N.E., Simpson, S.W., Quade, J., Cerling, T.E. and Frost, S.R., 2008. Herbivore enamel

US

carbon isotopic composition and the environmental context of Ardipithecus at Gona, Ethiopia.

AN

Geol Soc Am Spec Pap, 446, 215-234.

M

Levin, N.E., Brown, F.H., Behrensmeyer, A.K., Bobe, R. and Cerling, T.E., 2011. Paleosol

ED

carbonates from the Omo Group: Isotopic records of local and regional environmental change in

PT

East Africa. Palaeogeogr Palaeoclimatol Palaeoecol, 307, 75-89.

CE

Levin, N.E., Haile-Selassie, Y., Frost, S.R. and Saylor, B.Z., 2015. Dietary change among hominins and cercopithecids in Ethiopia during the early Pliocene. Proc Natl Acad Sci USA,

AC

112, 12304-12309.

O'Leary, M. H., 1981. Carbon isotope fractionation in plants. Phytochemistry, 20, 553-567.

O'Leary, M. H., 1988. Carbon isotopes in photosynthesis. Bioscience, 38, 328-336.

ACCEPTED MANUSCRIPT Passey, B.H., Cerling, T.E., 2002. Tooth enamel mineralization in ungulates: implications for recovering a primary isotopic time-series. Geo Cosm Acta, 66, 3225-3234.

Passey, B.H., Robinson, T.F., Ayliffe, L.K., Cerling, T.E., Sponheimer, M., Dearing, M.D.,

T

Ehleringer, J.R., 2005. Carbon isotope fractionation between diet, breath CO2, and

CR

IP

bioapatite in different mammals. J Archaeol Sci, 32, 1459-1470.

Potts, R., Behrensmeyer, A.K. and Ditchfield, P., 1999. Paleolandscape variation and Early

US

Pleistocene hominid activities: members 1 and 7, Olorgesailie Formation, Kenya. J Hum Evol,

AN

37, 747-788.

M

Quade, J. and Levin, N.E., 2013. East African hominid paleoecology: Isotopic evidence from

ED

paleosols. In: Sponheimer, M., Lee-Thorp, J.A., Reed, K.E.., and Ungar, P.S. (Eds.), Early

PT

hominin paleoecology. University Press of Colorado, Boulder, Colorado, 59-102.

CE

Quinn, R.L., Lepre, C.J., Wright, J.D. and Feibel, C.S., 2007. Paleogeographic variations of pedogenic carbonate δ13C values from Koobi Fora, Kenya: implications for floral compositions

AC

of Plio-Pleistocene hominin environments. J Hum Evol, 53, 560-573.

Quinn, R.L., Lepre, C.J., Feibel, C.S., Wright, J.D., Mortlock, R.A., Harmand, S., Brugal, J.P., Roche, H., 2013. Pedogenic carbonate stable isotopic evidence for wooded habitat preference of early Pleistocene tool makers in the Turkana Basin. J Hum Evol, 65, 65-78.

ACCEPTED MANUSCRIPT Reed, K.E. 2008. Paleoecological patterns at the Hadar hominin site, Afar regional state, Ethiopia. J Hum Evol, 54, 743-768.

Robinson, J.R., Rowan, J., Campisano, C.J., Wynn, J.G., and Reed, K.E., 2017. Late Pliocene

T

environmental change during the transition from Australopithecus to Homo. Nature Ecology and

CR

IP

Evolution, 0159.

Sikes, N.E., Potts, R. and Behrensmeyer, A.K., 1999. Early Pleistocene habitat in Member 1

AN

US

Olorgesailie based on paleosol stable isotopes. J Hum Evol, 37, 721-746.

Sponheimer, M., Lee-Thorp, J.A., 1999a. Alteration of enamel carbonate environments during

ED

M

fossilization. J Archaeol Sci, 26, 143–150.

Sponheimer, M., Lee-Thorp, J.A., 1999b. Oxygen isotopes in enamel carbonate and their

CE

PT

ecological significance. J Archaeol Sci, 26, 723–728.

Sponheimer, M., Lee-Thorp, J. A., DeRuiter, D., Smith, J., van der Merwe, N., Reed, K.E.,

AC

Grant, C., Ayliffe, L., Robinson, T., Heidelberger, C., Marcus, W., 2003. Diets of southern African Bovidae: stable isotope evidence. J Mammal, 84, 471–479.

Sponheimer, M., Alemseged, Z., Cerling, T.E., Grine, F.E., Kimbel, W.H., Leakey, M.G., LeeThorp, J.A., Manthi, F.K., Reed, K.E., Wood, B.A. and Wynn, J.G., 2013. Isotopic evidence of early hominin diets. Proc Natl Acad Sci USA, 110, 10513-10518.

ACCEPTED MANUSCRIPT Tejada-Lara, J.V., MacFadden, B.J., Bermudez, L., Rojas, G., Salas-Gismondi, R., Flynn, J.J., 2018. Body mass predicts isotope enrichment in herbivorous mammals. Proceedings of the Royal Society B: Biological Sciences 285, 20181020.

IP

T

Tiezsen, L.L., Senyimba, M.M., Imbaba, S.K., Troughton, J.H., 1979. The distribution of C 3 and C4 grasses and carbon isotope discrimination along an altitudinal and moisture gradient in

US

CR

Kenya. Oecologia, 37, 337-350.

Tiezsen, L.L., Boutton, T., Tesdahl, K., Slade, N., 1983. Fractionation and turnover of stable

AN

carbon isotopes in animal tissues: implications for the

C analysis of diet. Oecologia, 57,

M

32–37.

13

ED

Ungar, P.S., Abella, E.F., Burgman, J.H., Lazagabaster, I.A., Scott, J.R., Delezene, L.K., Manthi,

PT

F.K., Plavcan, J.M. and Ward, C.V. 2017. Dental microwear and Pliocene paleocommunity ecology of bovids, primates, rodents, and suids at Kanapoi. J Hum Evol, DOI:

AC

CE

10.1016/j.jhevol.2017.03.005

Uno, K.T., Polissar, P.J., Jackson, K.E., 2016a. Neogene biomarker record of vegetation change in eastern Africa. Proc Natl Acad Sci USA, 113, 6355-6363.

Uno, K.T., Polissar, P.J., Kahle, E., Feibel, C., Harmand, S., Roche, H., 2016b. A Pleistocene palaeovegetation record from plant wax biomarkers from the Nachukui Formation, West Turkana, Kenya. Phil Trans R Soc B, 373, 20150235.

ACCEPTED MANUSCRIPT

van der Merwe, N.J., Medina, E., 1991. The canopy effect, carbon isotope ratios and foodwebs in Amazonia. J Archaeol Sci, 18, 249-259.

T

Villmoare, B., Kimbel, W.H., Seyoum, C., Campisano, C.J., DiMaggio, E.N., Rowan, J., Braun,

IP

D.R., Arrowsmith, J.R. and Reed, K.E., 2015. Early Homo at 2.8 Ma from Ledi-Geraru, Afar,

CR

Ethiopia. Science, 347, 1352-1355.

US

Wang, Y., Cerling, T.E., 1994. A model of fossil tooth and bone diagenesis: implications for

AN

paleodiet reconstruction from stable isotopes. Palaeogeogr Palaeoclimatol Palaeoecol, 107, 281-

M

289.

ED

Werdelin, L., 2010. Chronology of Neogene Mammal Localities. In: Werdelin, L., and Sanders, W.J. (Eds.). Cenozoic Mammals of Africa, University of California Press, Los Angeles, pp. 27-

CE

PT

44.

Western, D. and Behrensmeyer, A.K., 2009. Bone assemblages track animal community

AC

structure over 40 years in an African savanna ecosystem. Science, 324, 1061-1064.

White, T.D., WoldeGabriel, G., Asfaw, B., Ambrose, S., Beyene, Y., Bernor, R.L., Boisserie, J.R., Currie, B., Gilbert, H., Haile-Selassie, Y., Hart, W.K., Hlusko, L.J., Howell, F.C., Kono, R.T., Lehmann, T., Louchart, A., Lovejoy, C.O., Renne, P.R., Saegusa, H., Vrba, E.S.,

ACCEPTED MANUSCRIPT Wesselman, H., Suwa, G., 2006. Asa Issie, Aramis and the origin of Australopithecus. Nature, 440, 883-889.

White, T.D., Ambrose, S.H., Suwa, G., Su, D.F., DeGusta, D., Bernor, R.L., Boisserie, J.-R.,

T

Brunet, M., Delson, E., Frost, S., Garcia, N., Giaourtsakis, I.X., Haile-Selassie, Y., Howell, F.C.,

IP

Lehmann, T., Likius, A., Pehlevan, C., Saegusa, H., Semprebon, G., Teaford, M., Vrba, E., 2009.

CR

Macrovertebrate paleontology and the Pliocene habitat of Ardipithecus ramidus. Science, 326,

US

87-93.

AN

Wood, B.A., Leakey, M.G., 2011. The Omo‐Turkana Basin Fossil Hominins and Their

M

Contribution to Our Understanding of Human Evolution in Africa. Evol Anthropol, 20, 264-292.

ED

WoldeGabriel, G., Ambrose, S.H., Barboni, D., Bonnefille, R., Bremond, L., Currie, B., DeGusta, D., Hart, W.K., Murray, A.M., Renne, P.R. and Jolly-Saad, M.C., 2009. The

PT

geological, isotopic, botanical, invertebrate, and lower vertebrate surroundings of Ardipithecus

CE

ramidus. Science, 326, 65-65e5.

AC

Wynn, J.G., 2000. Paleosols, stable carbon isotopes, and paleoenvironmental interpretation of Kanapoi, Northern Kenya. J Hum Evol, 39, 411-432.

Wynn, J.G., 2004. Influence of Plio‐Pleistocene aridification on human evolution: Evidence from paleosols of the Turkana Basin, Kenya. Am J Phys Anth, 123, 106-118.

ACCEPTED MANUSCRIPT Wynn, J.G., Sponheimer, M., Kimbel, W.H., Alemseged, Z., Reed, K., Bedaso, Z.K. and Wilson, J.N., 2013. Diet of Australopithecus afarensis from the Pliocene Hadar formation, Ethiopia. Proc Natl Acad Sci USA, 110, 10495-10500.

T

Wynn, J.G., Reed, K.E., Sponheimer, M., Kimbel, W.H., Alemseged, Z., Bedaso, Z.K. and

IP

Campisano, C.J., 2016. Dietary flexibility of Australopithecus afarensis in the face of

CR

paleoecological change during the middle Pliocene: Faunal evidence from Hadar, Ethiopia. J

US

Hum Evol, 99, 93-106.

AC

CE

PT

ED

M

Palaeoclimatol Palaeoecol, 416, 168-178.

AN

Zazzo, A., 2014. Bone and enamel carbonate diagenesis: a radiocarbon prospective. Palaeogeogr

ACCEPTED MANUSCRIPT Figure 1. Model of atmospheric and terrestrial carbon reservoirs indicating the fractionation chain from atmospheric CO 2 through vegetation to herbivore tooth enamel or paleosol carbonate. Fractionation is represented by the black arrows (except for the transition from vegetation to soil organic matter, where no fractionation is involved), and the difference between carbon isotope values at the ends of each arrow indicates the magnitude of isotopic enrichment, which is calculated as a function of the fractionation factor (see main text). As discussed in the text, we use + 14 ‰ as the fractionation factor for both herbivore enamel and paleosol carbonates.

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Figure 2. Map and schematic stratigraphic section of study sites (STUs) from the Turkana Basin, Kenya, and the Awash Valley, Ethiopia (blue, Koobi Fora Formation; purple, Nachukui Formation; red, Hadar Formation; orange, Sagantole Formation). Stratigraphic sections adapted from Werdelin (2010) and based on Campisano and Feibel (2007, 2008), Feibel (1999, 2011), and WoldeGabriel (2009).

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Figure 3. Scatter plots of taxon relative abundance from collections databases versus relative abundance of taxa sampled for δ13 C[enamel]. Points represent taxa used in this study (see Supplemental Dataset 3). Black lines represent a 1:1 relationship, with points falling above the 1:1 line representing taxa that are overrepresented in the δ13 C[enamel] sample relative to their collection abundances (red), and vice versa for points falling below the 1:1 line (blue). The colors of STU names indicate which geological formation they belong to (following Figure 2).

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Figure 4. Mirrored bar plots comparing distributions for δ13 C[enamel] (top gray) and δ13 C[pc] (bottom black). δ 13 C values for both enamel and paleosol carbonates are binned, with bin widths set at one per mil (‰). Number of sampled individuals for which there are δ 13 C[enamel] values are standardized using taxon relative abundance data from faunal databases (see Materials and Methods). δ13 C[pc] counts are standardized by the total number of paleosol samples in each STU. The colors of STU names indicate which geological formation they belong to (following Figure 2).

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Figure 5. Scatter plots comparing each STU’s (A) paleosol carbonate and weighted enamel δ 13 C median values, (B) paleosol carbonate and weighted enamel δ13 C interquartile range (IQR), and (C) paleosol carbonate and enamel sample size. Enamel isotope values are weighted using taxon relative abundances from faunal databases. Black lines are 1:1 lines. The color of points corresponds to which geological formation each STU belongs to (following Figure 2). Figure 6. Comparison of each STU’s observed paleosol carbonate interquartile range (IQR) (asterisk) to the distribution of interquartile ranges from 1,000 iterations of subsampled δ13 C[enamel] values (gray histograms) (to account for the larger enamel sample sizes). P-values are from one-tailed tests, calculating the proportion of subsampled enamel IQRs that is less than or equal to the observed paleosol carbonate IQR. “NA”s indicate which STUs have larger sample sizes for paleosol carbonates relative to enamel, which precludes the need for subsampling. Colors of STU names indicate which geological formation they belong to (following Figure 2). Figure 7. Comparing δ 13 C[pc] IQR calculated including reported averaged δ 13 C[pc] values versus simulated raw δ 13 C[pc] values. Each reported averaged δ 13 C[pc] value represents a mean of multiple samples (range = 2-4), while each set of simulated raw values represents a random draw

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from a normal distribution whose mean, standard deviation, and sample size are equivalent to those for each reported averaged δ 13 C[pc] value (1,000 iterations). Those STUs which have no averaged δ 13 C[pc] values are excluded from this analysis. Each point is an STU whose size is proportional to the percentage of that STU’s δ 13 C[pc] data which are averaged values. For the yaxis and over all 1,000 simulated iterations, each point represents the mean IQR calculated when each averaged δ 13 C[pc] value is represented by simulated raw values, and error bars indicate ±1 standard error. Large standard errors are due to the small number of samples represented by each averaged δ 13 C[pc] value. Dotted line is the 1:1 line and when used as the linear model, R2 = 0.79.

ACCEPTED MANUSCRIPT Table 1. Summary of each STU’s represented amount of space and time, approximate age range, enamel and paleosol δ 13 C sample sizes, and hominin taxa present. See Figure 2 for a map of sites. Space-time Unit (STU)

Area (km2 )a

Age Rang e (Ma)

Sample Sizeb

Tim e spa n (Ma )

Enam el 101

Paleos ol 44

Hominin Taxac

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Formati on

Sagantol e

Aramis

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4.404.40

<0.0 1

Ardipithecus ramidus

Hadar

Sidi Hakoma Denen Dora Kada Hadar

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0.16 0.06 0.26

76 132 107

10 9 12

East Turkana, Turkana Basin (4.0°N/36.37° E)

Koobi Fora

Lokochot Tulu Bor upper Burgi KBS Okote

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3.423.26 3.263.20 3.202.94 3.603.44 3.443.07 2.001.87 1.871.56 1.561.38

0.16 0.37 0.13 0.31 0.18

19 17 181 181 93

34 31 63 168 48

West Turkana, Turkana Basin (3.93°N/25.77 °E)

Nachukui

3.973.44 3.443.00 3.002.33 2.331.87 1.871.55 1.551.30 1.300.75

0.53 0.44 0.67 0.46 0.32 0.25 0.55

12 108 53 35 36 21 24

28 38 35 37 63 12 5

Australopithecus afarensis Australopithecus afarensis Australopithecus afarensis Hominini gen. et. sp. indet. Australopithecus afarensis Homo spp./Paranthropus boisei Homo spp./Paranthropus boisei Homo spp./Paranthropus boisei Australopithecus sp./Kenyanthropus platyops Australopithecus sp./Kenyanthropus platyops Paranthropus aethiopicus/Paranthr opus boisei Hominini gen. et. sp. indet. Homo erectus/Paranthropus boisei Homo erectus Homo erectus

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Kataboi lower/middle Lomekwi upper Lomekwi/Lokal alei Kalochoro Kaitio Natoo Nariokotome

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Middle Awash, Afar (10.5°N/40.5° E) lower Awash, Afar (11.1°N/40.58 °E)

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Region

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Approximate amount of area (as an order of magnitude estimate) represented by each formation’s STU. The area estimate can be thought of as a convex hull encompassing all samples within an STU.

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Stable carbon isotope data come from Aronson et al. (2008), Cerling et al. (2015), Harmand et al. (2015), Levin et al. (2011), Levin (2015), Quinn et al. (2007), Quinn et al. (2013), White et al. (2009), Woldegabriel et al. (2009), and Wynn et al. (2016). Sample sizes are those used in this study. c Hominin identifications are based on Kimbel et al. (2004), White et al. (2009), and Wood and Leakey (2011).

ACCEPTED MANUSCRIPT Table 2. Summed relative abundances of taxa sampled for isotopes as derived from faunal databases for each STU (i.e., summed abundances of sampled taxa divided by total abundances of sampled and unsampled taxa).

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Relative Abundance 0.974 0.815 0.974 0.920 0.661 0.575 0.790 0.928 0.684 0.416 0.727 0.856 0.877 0.767 0.557 0.852

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Space-time Unit (STU) Aramis Sidi Hakoma Denen Dora Kada Hadar Lokochot Tulu Bor upper Burgi KBS Okote Kataboi L/M Lomekwi U Lomekwi and Lokalalei Kalochoro Kaitio Natoo Nariokotome

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Formation Sagantole Hadar

ACCEPTED MANUSCRIPT Highlights Median δ 13 C values are typically greater in enamel than in paleosols at the same locality

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Variation in δ 13 C values is usually smaller in paleosols relative to enamel

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These two δ 13 C proxies record paleovegetation at different spatiotemporal scales

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Being aware of scale in habitat reconstructions is key to studying human evolution

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