Relative abundance of grazing and browsing herbivores is not a direct reflection of vegetation structure: Implications for hominin paleoenvironmental reconstruction

Ecomorphology in Kenya's Koobi Fora Formation: Reconstructing Early Pleistocene hominin paleoenvironments with 3D geometric morphometric analyses of bovid metapodials

This research presents a new method of ecological morphology (ecomorphology) analysis using three-dimensional geometric morphometrics to quantify shape variation in extant bovid metapodials with known habitat preferences. Extant data were used to create a model for classifying bones into distinct habitat categories and to test functional hypotheses related to locomotor behavior in different habitats. The model was then applied to fossils from the Koobi Fora Formation, Kenya, to assess the environmental context during important events in hominin evolution. The use of three-dimensional geometric morphometrics demonstrates significant improvement over traditional methods using caliper measurements. Discriminant function analysis successfully classified 94% of metacarpals and 93% of metatarsals into their correct habitat categories for modern specimens. The protocol was reduced to a subset of landmarks focused on the distal epiphyses. This model produced greater overlap, but classification success rates remained high, with 82% and 83% correct classification for modern metacarpals and metatarsals, respectively. We applied the reduced model to metapodials from Upper Burgi (1.98-1.87 Ma), KBS (1.87-1.56 Ma), and Okote (1.56-1.38 Ma) members in the Koobi Fora Formation. This location is important to understanding human evolution, fossil diversity, and paleoecology. Moreover, previous studies on faunal abundance, paleosol carbonates, and carbon isotopes provide a robust framework to compare the findings of this study. Our analyses classified the majority of fossil specimens as open-habitat dwellers, with a few specimens grouped as closed-adapted, the highest number of these falling within the Okote Member sample. This suggests that open and likely xeric environments dominated the East Turkana region during the Early Pleistocene. These findings are consistent with many previous reconstructions, though with a more open signal for the Okote Member than expected based on bovid abundance research.

The large mammal fossil fauna of the Cradle of Humankind, South Africa: a review

South Africa's Cradle of Humankind UNESCO World Heritage Site has remained the single richest source of hominin fossils for over ninety years. While its hominin specimens have been the subject of extensive research, the same is not true for its abundant faunal assemblages, despite their value in Plio-Pleistocene palaeoenvironmental reconstructions. Moreover, precise ages and depositional histories have been historically difficult to assess, though advancements in both relative and absolute dating techniques are changing this. This review explores the history of non-hominin large mammal faunal reporting, palaeoenvironmental reconstructions based on these fauna, and dating histories (with a focus on biochronology) at the following eight fossil-bearing sites of the Cradle that have been radiometrically dated with uranium-lead: Bolt's Farm, Cooper's Cave, Drimolen, Haasgat, Hoogland, Malapa, Sterkfontein and Swartkrans. Continued efforts to provide more precise and direct ages for sites using a variety of methods indicate that the bulk of Cradle deposits date to between 3 and 1.4 Ma. We find that, across almost all eight sites, there is little discussion or debate surrounding faunal reports, with some sites described by a single publication. Many of the reports are decades old with little review or reanalysis in the years following, emphasising the need for reviews such as this one. Our analysis of the data indicates that faunal-based paleoenvironmental reconstructions across sites commonly show a trend of wooded landscapes giving way to grasslands. We find that these reconstructions are primarily based on faunal abundance data, despite the availability of many other informative analytical techniques. The findings of this review highlight a need for more extensive and robust faunal reporting, as this will aid in understanding the context of these Cradle sites.

Modern African ecosystems as landscape-scale analogues for reconstructing woody cover and early hominin environments

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.

Oxygen isotopes in orangutan teeth reveal recent and ancient climate variation

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially produced growth layers, such as in corals, shells, and tree rings, as well as in accretionary deposits-ice and sediment cores, and speleothems. Oxygen isotopic compositions (δ18O) of tooth enamel are a direct method of reconstructing environmental variation experienced by an individual animal. Here, we utilize long-forming orangutan dentitions (Pongo spp.) to probe recent and ancient rainfall trends on a weekly basis over ~3-11 years per individual. We first demonstrate the lack of any consistent isotopic enrichment effect during exclusive nursing, supporting the use of primate first molar teeth as environmental proxies. Comparisons of δ18O values (n=2016) in twelve molars from six modern Bornean and Sumatran orangutans reveal a high degree of overlap, with more consistent annual and bimodal rainfall patterns in the Sumatran individuals. Comparisons with fossil orangutan δ18O values (n=955 measurements from six molars) reveal similarities between modern and late Pleistocene fossil Sumatran individuals, but differences between modern and late Pleistocene/early Holocene Bornean orangutans. These suggest drier and more open environments with reduced monsoon intensity during this earlier period in northern Borneo, consistent with other Niah Caves studies and long-term speleothem δ18O records in the broader region. This approach can be extended to test hypotheses about the paleoenvironments that early humans encountered in southeast Asia.

Pliocene hominins from East Turkana were associated with mesic environments in a semiarid basin

During the middle Pliocene (∼3.8-3.2 Ma), both Australopithecus afarensis and Kenyanthropus platyops are known from the Turkana Basin, but between 3.60 and 3.44 Ma, most hominin fossils are found on the west side of Lake Turkana. Here, we describe a new hominin locality (ET03-166/168, Area 129) from the east side of the lake, in the Lokochot Member of the Koobi Fora Formation (3.60-3.44 Ma). To reconstruct the paleoecology of the locality and its surroundings, we combine information from sedimentology, the relative abundance of associated mammalian fauna, phytoliths, and stable isotopes from plant wax biomarkers, pedogenic carbonates, and fossil tooth enamel. The combined evidence provides a detailed view of the local paleoenvironment occupied by these Pliocene hominins, where a biodiverse community of primates, including hominins, and other mammals inhabited humid, grassy woodlands in a fluvial floodplain setting. Between <3.596 and 3.44 Ma, increases in woody vegetation were, at times, associated with increases in arid-adapted grasses. This suggests that Pliocene vegetation included woody species that were resilient to periods of prolonged aridity, resembling vegetation structure in the Turkana Basin today, where arid-adapted woody plants are a significant component of the ecosystem. Pedogenic carbonates indicate more woody vegetation than other vegetation proxies, possibly due to differences in temporospatial scale and ecological biases in preservation that should be accounted for in future studies. These new hominin fossils and associated multiproxy paleoenvironmental indicators from a single locale through time suggest that early hominin species occupied a wide range of habitats, possibly including wetlands within semiarid landscapes. Local-scale paleoecological evidence from East Turkana supports regional evidence that middle Pliocene eastern Africa may have experienced large-scale, climate-driven periods of aridity. This information extends our understanding of hominin environments beyond the limits of simple wooded, grassy, or mosaic environmental descriptions.