Project 1

Bone Modification Paleoscape

The Pliocene paleoscape context of the origins of technology
Two cut marks made by stone tools on the rib of a cow sized mammal

Principal Investigators

Project 1 uses a novel approach to the empirical study of hominin butchery–a potential sign of enhanced social learning–and other agents of bone-surface modification in the first extensive sample of middle Pliocene (3.4 Ma) fossils amassed for this purpose through new field work in the critical but poorly known time period between 2.9 and 2.6 Ma.

This project addresses the “complex cognition” aspect of our research paradigm by testing the possibility of the development of a stage of stone tool use that predated shaped stone tools. To understand the pace of cumulative culture, we need to fix in time when different technological phases originated. This project targets the earliest phase of interplay between complex cognition and cumulative culture.

Detailed Project Description

Functional links among stone-tool manufacture, enhanced cognition, and meat-eating have been at the center of anthropological theorizing since Darwin’s time. Regular consumption of meat protein, either through scavenging or hunting, represents a critical adaptive shift usually associated with the origin of Homo; supporting evidence comes from the broad contemporaneity of Oldowan tools, stone-tool marked mammalian bone, and at least modestly encephalized skulls of early Homo species, sometimes in the same stratigraphic horizons, by ca. 2.0 Ma. Evidence of stone tool manufacture and cut-marked bone at 2.5-2.6 Ma points to an older linkage, although the paucity of hominin fossils from this time period makes it impossible to tie the implied butchery behaviors to any specific taxon or taxa. Contemporaneous (and earlier) Australopithecus (sensu lato) is usually thought to have been technologically pre-lithic, but there are circumstantial and theoretical reasons for thinking that stone tool use, if not manufacture, has even more ancient roots in the hominin lineage. The manufacture of stone tools indicates enhanced social learning capabilities beyond the occasional use of unshaped flakes by our great ape cousins. Therefore, determining when, where, and under what environmental circumstances the first stone tools were used is of paramount significance.

These ideas have been highlighted by the recovery of two fossil bone fragments of medium to large size mammals bearing evidence of stone-tool cutting and percussion from ca. 3.3-3.4 Myr-old Hadar Formation sediments at Dikika, Ethiopia. These bones pre-date the earliest evidence of butchery for meat procurement by ca. 0.8 myr. No flaked stone tools have yet been found in these sediments, and debate has ensued regarding the identification of the bone-modifying agents in the Dikika cases.

Methods

We propose to undertake the first large-sample analysis of fossil-bone surface modification using three-dimensional geometric morphometric methods. The Dikika bone surface modification identifications were originally done with “expert-knowledge,” using three blind-tested analysts to classify the marks. The resulting debate highlights the need to develop objective computer-based classificatory approaches. Using high-resolution 3D scanners, we scanned the marks of a wide variety of surface modifications in modern bone assemblages (crocodiles, hyenas, stone tool cutmarks, stone tool percussion marks, and trampling marks) and then subjected them to morphometric analysis. Our results from the initial analysis of this small sample suggests that most of the marks can be statistically differentiated. We propose to significantly enlarge the samples and variation of the agents to develop robust machine-based systems of mark analysis that will allow us to analyze samples with great statistical power. The new 3D imaging laboratory, funded by this research program, will be used for this analysis.

In conjunction with this analytical approach, we will also expand field work to characterize the “bone-surface modification paleoscape.” While much of the attention devoted to the Dikika results has focused on the identifications of agents of modification, and thus on the discovery of the earliest evidence for tool use, a new approach to field collecting defines the population of bone-surface modification across paleo-landscapes as a new way to illuminate the ecology of early hominins. A landscape has a pattern of surface modification that is a direct trace of the interactions of ancient carnivores and their prey in different habitat settings. Carcass competition and predation risk vary across landscapes and are reflected in the bones and their surface modification. Our field localities at the Hadar site (adjacent to, and overlapping in time with, the Dikika site) preserve pieces of these differing habitats, and a study that defined as continuous data the “surface modification paleoscape” would be able to not only define the presence and abundance of surface damage potentially attributable to hominins, but could situate it within a broader reconstruction of the activities of carnivores and their prey across the ancient ecosystem. Studies of the “bone-surface modification paleoscape” have never been attempted at these timescales, and we propose to conduct such a study. Similar studies are ongoing at Olduvai Gorge, Tanzania, and as that material is published, we will be able to compare the Hadar results to those attributable to early Homo so as to detect any significant changes from a hominin that is likely using, but not making tools, to an undoubted early tool maker.

In 2012, the IHO team led field work at the Hadar site, which contains deposits of the same 3.3-3.4 myr-old Sidi Hakoma Member unit that yielded the cut-marked fossils from nearby Dikika (the two sites are separated by the Awash River). Under the direction of archaeologist and bone-modification expert Jessica Thompson, data were recorded from more than 15,000 fossil specimens following a paleo-landscape approach to sampling by following specific silt and sand horizons over more than 1 km. More than 1,500 modified specimens were collected for analysis—a unique sample in the mid-Pliocene African paleontological record.

We will apply our 3D high-resolution imaging and morphometric techniques (facilitated by the IHO imaging lab) to these and other new field samples from Hadar to define the patterning of surface modification across these ancient landscapes and thus determine if and how frequently early hominins were involved in carnivory. This will inform us on the origins of technology, in what habitats early hominins interacted with carcasses, and what the pattern of carcass use by other predators was like across this landscape. The verification of a pre-Homo emergence of lithic technology, potentially signaled by stone-modified mammalian bone during the era of small-brained but bipedal Australopithecus, would fundamentally question the presumed linkage of stone-tool use/manufacture, brain-size increase, and the origin of our own genus—and thus open up new questions and hypothesis about the triggers of cultural evolution in Homo.