In humid, continental Michigan, we identified pedogenic carbonate in a soil profile developed on glacial drift sediments, as rinds, rhizoliths, and filaments (at depths >50 cm). Given that the climate setting is unusual for pedogenic carbonate, we investigated its formation with environmental monitoring and isotope analyses of carbonate (delta C-13, delta O-18, Delta(47), and C-14) and waters (delta O-18 and delta H-2). We found covariation in delta C-13 and Delta(47) amongst the carbonate types (rhizoliths, rinds, filaments, bulk soil, and detrital clasts), and C-14 ages of rinds that predate plausible formation ages. The delta C-13 and Delta(47) values of the bulk carbonate and some of the pedogenic morphologies are not fully compatible with pedogenic formation in the modern environment. The delta O-18 data from precipitation and river waters and from carbonates are not uniquely identifying; they are compatible with the soil carbonate being pedogenic, detrital, or a mix. We conclude that the soil carbonate is likely a physical mix of pedogenic and detrital carbonate. Pedogenic carbonate is forming in this humid setting, likely because seasonal cycles in soil respiration and temperature cause cycles of dissolution and re-precipitation of detrital and pedogenic carbonate. The pedogenic carbonate may be a transient feature as carbonate-rich till undergoes post-glacial chemical weathering.

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) of incrementally grown tissues have been used to study movement and migration of animals. Despite advances in characterizing ⁸⁷Sr/⁸⁶Sr turnover [1], the 2-D geometry of turnover in the tooth enamel is still poorly understood. The relocation of a zoo elephant (Loxodonta africana) named Misha provided an exceptional case study for understanding this pattern [1]. We documented the ⁸⁷Sr/⁸⁶Sr turnover in Misha’s molar using high-resolution in situ measurements with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).We prepared a longitudinally-cut thick section from Misha’s molar plate for LA-ICP-MS analysis. Within the tooth enamel, we measured 10 LA-ICP-MS transects parallel to the enamel dentine junction (EDJ), to map the 2-D pattern of ⁸⁷Sr/⁸⁶Sr turnover. Within the dentine, we measured a transect adjacent to the EDJ to document the unattenuated ⁸⁷Sr/⁸⁶Sr turnover sequence. We also analyzed conventionally drilled enamel samples from the same molar plate using the solution method for ⁸⁷Sr/⁸⁶Sr to document any turnover signal attenuation.Molar dentine data are consistent with the published Sr turnover pattern in Misha’s tusk dentine. The inner half of the molar enamel preserves the turnover features in high fidelity, with a 2-D turnover geometry closely following that of enamel apposition. By contrast, the middle to outer surface of the enamel shows progressively more elevated ⁸⁷Sr/⁸⁶Sr values than those of the dentine. Data from drilled enamel samples show an attenuated turnover pattern due to averaging during drilling, as well as more elevated ⁸⁷Sr/⁸⁶Sr. We attribute these elevated Sr ratios to post-relocation Sr overprinting primarily on the outer enamel surface during enamel maturation.Our results suggest that in situ LA-ICP-MS analysis of the inner half of enamel best recovers the time scale and magnitude of the ⁸⁷Sr/⁸⁶Sr turnover in an elephant molar. By contrast, the attenuated and overprinted turnover sequence from conventionally drilled enamel samples may lead to biased interpretations of the timing and geospatial scale of the animal’s movement history. To properly interpret conventionally drilled enamel sequences, future work would benefit from a modeling framework that can account for attenuation, overprint, and turnover of Sr, to quantitatively reconstruct movement or life history of extant and extinct animals. References:[1] Yang, D., Bowen, G. J., Uno, K. T., Podkovyroff, K., Carpenter, N. A., Fernandez, D. P., & Cerling, T. E. (2023). BITS: A Bayesian Isotope Turnover and Sampling model for strontium isotopes in proboscideans and its potential utility in movement ecology. Methods in Ecology and Evolution, 14, 2800–2813. https://doi.org/10.1111/2041-210X.14218

Dietary shifts and corresponding morphological changes can sometimes evolve in succession, not concurrently—an evolutionary process called behavioral drive. Detecting behavioral drive in the fossil record is challenging because it is difficult to measure behaviors independently from corresponding morphologies. To solve this problem, we focused on a puzzling behavior in the fossil record of some primates: eating graminoid plants. We report carbon and oxygen isotope ratios from fossil cercopithecid monkeys and integrate the data into a view of hominin dietary evolution, finding that changes in graminivorous behavior preceded corresponding changes in dental morphology by ~700,000 years. Decoupling diets and morphologies in time was conducive to determining when and to exploring why dietary changes helped to propel human evolution.

Strontium isotope ratios (87Sr/86Sr) in dental tissues are widely used to study animal and human migration. However, questions remain regarding how different biological processes and sampling methods influence measured 87Sr/86Sr and subsequent interpretations. We present a unique experiment with the known relocation history of a zoo elephant to evaluate the influence of biological turnover, tissue type, and sampling methods. We collected 87Sr/86Sr data from the elephant's tusk and molar enamel using in-situ laser ablation microsampling, conventional drilling, and micromilling techniques. Our data comparisons show that the innermost enamel best records the primary 87Sr/86Sr turnover history, while enamel maturation affects outer enamel 87Sr/86Sr. Conventional drilling and micromilling show attenuated 87Sr/86Sr records due to enamel maturation and sample averaging. To effectively account for 87Sr/86Sr signal attenuation due to turnover, we demonstrated a microsampling-modeling workflow using our tusk and enamel data. This recommended workflow can facilitate geospatially explicit interpretations of seasonal migration.

The continental fossil record has exceptional, long sequences of fossiliferous strata that are the basis for evaluating ecosystem dynamics and their formative influences. The Siwalik sequence of South Asia is one example. It occurs in the Potwar Plateau (Punjab Province, Pakistan) and spans 18–1 Ma. The sequence consists of alluvial sediments deposited in a foreland basin created by the collision of the Indian and Eurasian tectonic plates. Sediments representing large and small river channels and their associated floodplain deposits correspond to mountain-sourced large rivers and foothill-sourced smaller rivers. Vegetation attributes are recorded in stable carbon isotopes and biomarkers in paleosols. Molluscs, fishes, crocodilians, turtles, lizards, snakes, birds, and mammals are preserved throughout the sequence. Mammalian faunas had exceptionally high species richness (116 species) at their peak and included up to 18 species of co-occurring megaherbivores (>800 kg). Significant changes over time in species richness, taxonomic composition, and ecological structure of mammalian faunas coincided with major changes in climate and vegetation. ▪ Siwalik strata and fossils document a long continuous sequence of South Asian continental sediments and ecosystems south of the Himalaya Mountains. ▪ A multidisciplinary analysis of tectonics, fluvial systems, climate history, and vertebrate diversity documents ecosystem dynamics from 18 to 6 million years ago. ▪ A sparse portion of the Siwalik record coinciding with the Miocene Climatic Optimum raises the possibility that humid heat stress limited occupancy of the floodplain by most mammals for much of this time. ▪ The timing and magnitude of change in mammalian species richness and ecological structure are consistent with environmental forcing as a significant influence on these features.

Triple oxygen isotope values of xylem water were measured along the length of smooth horsetail stems (Equisetum laevigatum). Extreme isotope enrichment is observed moving from base to stem tip. δ18O values range from -8.3‰ at the base to 82.6‰ at the tip. Δ'17O values range from 0 to -1,797 per meg. The δ18O and Δ'17O values are the most extreme measured for any terrestrial material and expand the known range of Δ'17O values by fivefold for mass-dependent fractionation on Earth. The extreme isotope enrichments are explained using a hybrid evaporation/chain-of-lakes model, allowing us to refine the leaf respiration coefficient to θk = 0.511 ± 0.001. This new value is required to explain the low Δ'17O values previously measured in desert plants and animals and is critical when using fossil samples for paleoclimate reconstruction. Coexisting phytoliths and stem water were also measured. The 1000ln18αsilica-water value at the plant base (35.89‰) appears to be in isotopic equilibrium, with far smaller fractionations of 10.3‰ near the tip. The smaller fractionations at higher levels are explained by continual silica deposition as the plant elongates and the δ18O values of each segment become higher. The overall integrated phytolith value is a combination of early and late silica growth. The Δ'17Osilica - Δ'17Owater values are not in equilibrium, explained by a kinetic isotope effect, with a λ value of 0.5205 vs. 0.5244 for equilibrium. Phytolith isotope values may lead to erroneous interpretations for paleoclimate reconstruction.

Although modern humans left Africa multiple times over 100,000 years ago, those broadly ancestral to non-Africans dispersed less than 100,000 years ago 1 . Most models hold that these events occurred through green corridors created during humid periods because arid intervals constrained population movements 2 . Here we report an archaeological site—Shinfa-Metema 1, in the lowlands of northwest Ethiopia, with Youngest Toba Tuff cryptotephra dated to around 74,000 years ago—that provides early and rare evidence of intensive riverine-based foraging aided by the likely adoption of the bow and arrow. The diet included a wide range of terrestrial and aquatic animals. Stable oxygen isotopes from fossil mammal teeth and ostrich eggshell show that the site was occupied during a period of high seasonal aridity. The unusual abundance of fish suggests that capture occurred in the ever smaller and shallower waterholes of a seasonal river during a long dry season, revealing flexible adaptations to challenging climatic conditions during the Middle Stone Age. Adaptive foraging along dry-season waterholes would have transformed seasonal rivers into ‘blue highway’ corridors, potentially facilitating an out-of-Africa dispersal and suggesting that the event was not restricted to times of humid climates. The behavioural flexibility required to survive seasonally arid conditions in general, and the apparent short-term effects of the Toba supereruption in particular were probably key to the most recent dispersal and subsequent worldwide expansion of modern humans.

Eastern Africa is home to the largest terrestrial migrations on Earth. Though these migratory systems have been well studied for decades, little is known of their antiquity and evolutionary history. Serially sampled strontium stable isotopes (87Sr/86Sr) from tooth enamel can be used to track migration in mammals. Here we analyse 87Sr/86Sr for 79 bovid and equid individuals representing 18 species from four localities in Kenya to characterize prehistoric migratory systems during the Last Glacial Period (115-11.7 ka). Of the species analysed, 16 lack definitive evidence for migration, including blue wildebeest (Connochaetes taurinus), Thomson's gazelle (Eudorcas thomsonii) and plains zebra (Equus quagga), which are long-distance migrants today in the Greater Serengeti Ecosystem and historically in the Athi-Kapiti Plains. Only two species, the extinct wildebeests Rusingoryx atopocranion and Megalotragus sp., were migratory. These findings suggest a possible alternative narrative about ecosystem dynamics during the Last Glacial Period and shed light on the behaviour of both extant and extinct species at this time. In particular, these results indicate that migratory behaviour in extant species either emerged during the Holocene or was more spatiotemporally constrained in the past. Our results contribute to a growing body of evidence suggesting that the structure and function of geologically recent large mammal communities in eastern Africa differed considerably from those observed in the present day. Analysing strontium isotope ratios for individuals of 18 bovid and equid species dating to the Last Glacial Period (115-11.7 ka), the authors find that 16 of these species lack definitive evidence of migration, even those species that are long-distance migrants today.

How animals respond to seasonal resource availability has profound implications for their dietary flexibility and realized ecological niches. We sought to understand seasonal dietary niche partitioning in extant African suids using intra-tooth stable isotope analysis of enamel. We collected enamel samples from canines of red river hogs/bushpigs (Potamochoerus spp.) and third molars of warthogs (Phacochoerus spp.) in 3 different regions of central and eastern Africa. We analyzed multiple samples from each tooth and used variations in stable carbon and oxygen isotope ratios (δ13C and δ18O) and covariances between them to infer seasonal dietary changes. We found that most Phacochoerus display C4-dominated diets, while most Potamochoerus display C3-dominated diets. Phacochoerus and Potamochoerus that co-occur in the same region display no overlap in intra-tooth δ13C, which suggests dietary niche partitioning. They also show diverging δ13C values as the dry seasons progress and converging δ13C values during the peak of the rainy seasons, which suggests a greater dietary niche separation during the dry seasons when resources are scarce than during the rainy season. We found statistically significant cross-correlations between intra-tooth δ13C and δ18O in most specimens. We also observed a temporal lag between δ13C and δ18O in some specimens. This study demonstrates that intra-tooth stable isotope analysis is a promising approach to investigate seasonal dietary niche variation. However, large inter-individual variations in δ18O at certain localities can be challenging to interpret. Future studies that expand the intra-tooth stable isotope surveys or include controlled feeding experiments will improve its application in ecological studies.

Strontium isotope ratios (87Sr/86Sr) of incrementally grown tissues have been used to study animal movement/migration. Despite growing interest in this tool, questions remain regarding how different dental tissues preserve the same 87Sr/86Sr input signal, and how different biological processes and sampling methods influence measured enamel 87Sr/86Sr. We collected 87Sr/86Sr data from tusk dentine and molar enamel of Misha, a zoo elephant with known movement history, using in situ laser ablation (LA-ICP-MS) mapping, conventional drilling, and micromilling techniques. We compared 87Sr/86Sr data from different substrates to evaluate the influence of turnover, tissue type, and sampling methods. Our LA-ICP-MS analysis showed a remarkable 87Sr/86Sr geometry consistent with enamel apposition. Enamel maturation affects 87Sr/86Sr primarily in the outer enamel. Conventional drilling and micromilling produced attenuated 87Sr/86Sr records due to enamel maturation and sample averaging. Caution should be taken when interpreting 87Sr/86Sr data from conventionally drilled enamel, which may bias reconstructions of movement/migration. Our results show that LA-ICP-MS of the innermost enamel with associated dental growth measurements can best recover the primary 87Sr/86Sr turnover history. However, biological turnover of 87Sr/86Sr is still the primary source of input signal attenuation and should be accounted for. We recommend a micro-sampling and inverse modeling workflow which we demonstrate using Misha’s tusk and enamel data. While a broader application of this approach would benefit from more experiments, it can facilitate quantitative interpretations of movement/migration histories and help answer questions of individual life history such as human/animal seasonal subsistence and reproductive patterns.

Reconstructing habitat types available to hominins and inferring how the paleo-landscape changed through time are critical steps in testing hypotheses about the selective pressures that drove the emergence of bipedalism, tool use, a change in diet, and progressive encephalization. Change in the amount and distribution of woody vegetation has been suggested as one of the important factors that shaped early hominin evolution. Previous models for reconstructing woody cover at eastern African hominin fossil sites used global-scale modern soil comparative datasets. Our higher-spatial-resolution study of carbon isotopes in soil organic matter is based on 26 modern African locations, ranging from tropical grass-dominated savannas to forests. We used this dataset to generate a new Eastern Africa -specific Woody Cover Model (EAWCM), which indicates that eastern African hominin sites were up to 13% more wooded than reconstructions based on previous models. Reconstructions using the EAWCM indicate widespread woodlands/bushlands and wooded grasslands and a shift toward C4-dominated landscapes in eastern Africa over the last 6 million years. Our results indicate that mixed tree-C4 grass savannas with 10-80% tree cover (but not pure grasslands with <10 % tree cover) dominated early hominin paleoenvironments. Landscapes with these biomes are marked by exceptional heterogeneity, which posed challenges and offered opportunities to early hominins that likely contributed to major behavioral and morphological shifts in the hominin clade. (c) 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution.

The Turkana Basin in NW Kenya and SW Ethiopia hosts remarkable fossil-rich sediments that are central to our understanding of early hominin evolution, with interbedded volcanic tuffs providing critical time markers. However, the resolution of existing Early Pleistocene–Pliocene ages is limited to c. 20–60 kyr, inhibiting the evaluation of climatic and environmental drivers of evolution. We present high-precision, single-feldspar 40 Ar/ 39 Ar age and elemental data for four stratigraphically significant tuffs. These samples exhibit variably dispersed age distributions correlated with feldspar compositional trends, interpreted to indicate the partial retention of inherited 40 Ar related to crustal ‘cold storage’ and rapid melt infiltration preceding eruption. We evaluated various statistical methods and calculated astronomically calibrated Bayesian age estimates of 1879.1 ± 0.6 ka (±2.4 ka including external errors) for the Kay Behrensmeyer Site (KBS)/H2 Tuff, 1837.4 ± 0.9 ka (±2.4 ka) for the Malbe/H4 Tuff, 1357.5 ± 1.8 ka (±2.5 ka) for the Chari/L Tuff and 1315.4 ± 1.9 ka (±2.5 ka) for the Gele Tuff. Our results permit refined age constraints for important early Homo fossils, including the cranium KNM-ER1813 ( Homo habilis ) and various Homo erectus fossils. The KBS Tuff age also provides an important calibration locus for orbital tuning of palaeoclimate proxy records, revealing the complex interplays between palaeoclimate and geological drivers of sedimentation. Supplementary material : The supplementary tables and figures include previously published ages (Table S1), sample and irradiation information (Table S2), electron probe microanalytical results for tuff glasses (Table S3, Figs S2 and S3) and feldspars (Table S4), 40 Ar/ 39 Ar analytical data (Tables S5 and S6, Fig. S4), orbital tuning model parameters (Table S7), a summary of previous and revised hominin ages (Table S8) and a worked Bayesian estimation example (Fig. S1) and are available at https://doi.org/10.6084/m9.figshare.c.6602994

Abstract Strontium isotope ratios (87Sr/86Sr) of incrementally grown tissues have been widely used to study movement ecology and migration of animals. However, the time scale of 87Sr/86Sr incorporation from the environment into tissue and how it may influence data interpretation are still poorly understood. Using the relocation of a zoo elephant (Loxodonta africana) named Misha, we characterise and model the 87Sr/86Sr turnover process using high‐resolution measurements of its tusk dentine. We seek to develop a framework that can improve quantitative interpretation of 87Sr/86Sr data in tissues. The 87Sr/86Sr transition associated with the relocation is measured using laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) on a prepared tusk slab. We develop a turnover model (BITS), with a rapidly exchanging central pool and a slowly exchanging peripheral pool, in a Bayesian statistical framework. The measured dentine data are first used to calibrate model parameters. The parameters are then used to estimate possible 87Sr/86Sr input time series from two datasets via model inversion: a fidelity test using Misha's dentine data and a case study using published dentine measurements from an Alaskan Woolly Mammoth (Mammuthus primigenius). The LA‐ICP‐MS data are consistent with a two‐compartment turnover process with equivalent half‐lives of 41 days for the central pool and 170 days for the peripheral pool. The model inversion shows good fidelity when estimating the intake 87Sr/86Sr time series associated with Misha's relocation. In the case study, the model suggests an abrupt pattern of change in, and a much wider range of, intake 87Sr/86Sr values than expressed in the woolly mammoth dentine data themselves. Our framework bridges the gap between environmental 87Sr/86Sr variation and data measured in tusk dentine or other incrementally grown tissues. It could be coupled with movement models and additional isotope tracers to study seasonal residency or the spatial and temporal patterns of movement/migration. The generic turnover processes can be adapted to other isotope systems, additional incremental tissues, or other organisms, thus expanding our modelling toolkit to investigate niche partitioning, life history traits and behavioural patterns in conservation biology, archaeology and paleoecology.

Individual animals should adjust diets according to food availability. We used DNA metabarcoding to construct individual-level dietary timeseries for elephants from two family groups in Kenya varying in habitat use, social position and reproductive status. We detected at least 367 dietary plant taxa, with up to 137 unique plant sequences in one fecal sample. Results matched well-established trends: elephants tended to eat more grass when it rained and other plants when dry. Nested within these switches from ‘grazing’ to ‘browsing’ strategies, dietary DNA revealed seasonal shifts in food richness, composition and overlap between individuals. Elephants of both families converged on relatively cohesive diets in dry seasons but varied in their maintenance of cohesion during wet seasons. Dietary cohesion throughout the timeseries of the subdominant ‘Artists’ family was stronger and more consistently positive compared to the dominant ‘Royals’ family. The greater degree of individuality within the dominant family's timeseries could reflect more divergent nutritional requirements associated with calf dependency and/or priority access to preferred habitats. Whereas theory predicts that individuals should specialize on different foods under resource scarcity, our data suggest family bonds may promote cohesion and foster the emergence of diverse feeding cultures reflecting links between social behaviour and nutrition.