Comparative isotopic evidence from East Turkana supports a dietary shift within the genus Homo.

It has been suggested that a shift in diet is one of the key adaptations that distinguishes the genus Homo from earlier hominins, but recent stable isotopic analyses of fossils attributed to Homo in the Turkana Basin show an increase in the consumption of C4 resources circa 1.65 million years ago, significantly after the earliest evidence for Homo in the eastern African fossil record. These data are consistent with ingesting more C4 plants, more animal tissues of C4 herbivores, or both, but it is also possible that this change reflects factors unrelated to changes in the palaeobiology of the genus Homo. Here we use new and published carbon and oxygen isotopic data (n = 999) taken from large-bodied fossil mammals, and pedogenic carbonates in fossil soils, from East Turkana in northern Kenya to investigate the context of this change in the isotope signal within Homo. By targeting taxa and temporal intervals unrepresented or undersampled in previous analyses, we were able to conduct the first comprehensive analysis of the ecological context of hominin diet at East Turkana during a period crucial for detecting any dietary and related behavioural differences between early Homo (H. habilis and/or H. rudolfensis) and Homo erectus. Our analyses suggest that the genus Homo underwent a dietary shift (as indicated by δ13Cena and δ18Oena values) that is (1) unrelated to changes in the East Turkana vegetation community and (2) unlike patterns found in other East Turkana large mammals, including Paranthropus and Theropithecus. These data suggest that within the Turkana Basin a dietary shift occurred well after we see the first evidence of early Homo in the region.

Hand grip diversity and frequency during the use of Lower Palaeolithic stone cutting-tools.

The suite of anatomical features contributing to the unique gripping capabilities of the modern human hand evolved alongside the proliferation of Lower Palaeolithic flaked tool technologies across the Old World. Experimental studies investigating their potential co-evolution suggest that the use of flakes, handaxes, and other stone tools is facilitated by manipulative capabilities consistent with the evolutionary trajectory of the hominin hand during this period. Grip analyses have provided important contributions to this understanding. To date, however, there has been no large-scale investigation of grip diversity during flaked stone-tool use, empirical comparative analyses of grip use frequencies, or examination of ergonomic relationships between grip choice and stone tool type and form. Here, we conduct four experimental studies, using replica Lower Palaeolithic stone tools in a series of actualistic and laboratory-based contexts, to record grip type and frequency of grip use during 1067 stone tool-use events by 123 individuals. Using detailed morphometric data recorded from each tool, we demonstrate how grip choice varies according to the type and form of stone tool used, and how these relationships differ between tool-use contexts. We identify 29 grip types across all tool-use events, with significant differences recorded in their frequency of use dependent on tool type, tool form, and the context of use. Despite the influence of these three factors, there is consistency in the frequent use of a limited number (≤4) of grip types within each experiment and the consistent and seemingly forceful recruitment of the thumb and index finger. Accordingly, we argue that there are deep-rooted, ergonomically-related, regularities in how stone tools are gripped during their use, that these regularities may have been present during the use of stone tools by Plio-Pleistocene hominins, and any subsequent selective pressures would likely have been focused on the first and second digit.

Investigating hominin carnivory in the Okote Member of Koobi Fora, Kenya with an actualistic model of carcass consumption and traces of butchery on the elbow.

Previous zooarchaeological analysis at Koobi Fora indicates that Okote Member hominins were the primary agents of bone assemblage formation, gained early access to large and small mammal flesh, and consumed both high- and low-ranked carcass parts. The discovery of additional butchered specimens prompted the re-analysis presented here of three large and well-preserved zooarchaeological assemblages from the Okote member, GaJi14, FwJj14N and FwJj14S, to revisit paleoecological hypotheses about tool-assisted carnivory. Cow and goat limb butchery documenting the skeletal location of cut marks created by skinning, defleshing, and disarticulation was used to build an actualistic model to infer hominin consumption of distinct carcass resources. Archaeological specimens were assigned to early (defleshing limbs), middle (defleshing ribs, viscera, vertebrae, and head) and late (metapodial tendon removal, element disarticulation, long bone fragmentation) carcass consumption stages, and the incidence of these butchery behaviors was examined for specimens and minimum number of element and individual aggregates. Elbow specimens, where traces of defleshing, disarticulation, and percussion co-occur, offer a sequential view of carcass consumption behaviors that is free from fragmentation bias. Classification trees populated with actualistic data were used to identify defleshing and disarticulation cut mark clusters on archaeological elbow portions by their location, cut mark count, median length, and median cross-sectional width. Actualistically-informed configurational analysis offers high-resolution behavioral reconstruction of the butchered sub-assemblage and should be integrated with assemblage-scale zooarchaeological methods. These experiments highlight the bias for detecting butchery traces of early carcass access, because defleshing cut marks are abundant and introduced to dense midshaft portions, whereas disarticulation cut marks are rare and occur on epiphyseal portions, which are often deleted by density-mediated destruction. Butchery trace interpretation across multiple analytical scales confirms a flexible carnivorous paleoecological role for Okote hominins that included primary and secondary access to carcass resources from large and small mammals.

A new high-resolution 3-D quantitative method for identifying bone surface modifications with implications for the Early Stone Age archaeological record.

Bone surface modifications have become important indicators of hominin behavior and ecology at prehistoric archaeological sites. However, the method by which we identify and interpret these marks remains largely unchanged despite decades of research, relying on qualitative criteria and lacking standardization between analysts. Recently, zooarchaeologists have begun using new technologies capable of capturing 3-D data from bone surface modifications to advance our knowledge of these informative traces. However, an important step in this research has been overlooked and after years of work, we lack both a universal and replicable protocol and an understanding of the precision of these techniques. Here we propose a new standard for identifying bone surface modifications using high-resolution 3-D data and offer a systematic and replicable approach for researchers to follow. Data were collected with a white-light non-contact confocal profilometer and analyzed with Digital Surf's Mountains® software. Our data show that when methods are standardized, results between researchers are statistically indistinguishable. Multivariate analyses using the measured parameters allow discrimination between stone tool cut marks and mammalian carnivore tooth marks with 97.5% accuracy. Application of this method to fossil specimens resulted in 100% correspondence with identifications made by an experienced analyst using macroscopic observations of qualitative features of bone surface modifications. High-resolution 3-D analyses of bone surface modifications have great potential to improve the reliability and accuracy of taphonomic research, but only if our methods are replicable and precise.