Pyrotechnology through a zooarchaeological perspective: experimental data on burned bone and their application to Neanderthal fire use at Roc de Marsal (France)
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Pyrotechnology through a zooarchaeological perspective: experimental data on burned bone and their application to Neanderthal fire use at Roc de Marsal (France)

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A central point for nearly all disciplines of paleoanthropology remains the desire to describe, understand, and contextualize the diverse behavior of hominins and the emergence of modern human behavior. These compelling questions are at the forefront of studies which consider the archaeology of Homo sapiens and Neanderthals, our close genetic cousins, and prompt us to reconsider what it means and what it has meant to be human.Neanderthals are estimated to be phenotypically extinct around 40,000 years ago, despite sharing a genetic legacy with all non-exclusively African populations of modern Homo sapiens (Prüfer et al., 2014). It is currently reconstructed through genetic and archaeological data that the last Neanderthals shared a landscape with contemporaneous Homo sapiens groups in Western Europe (overlap estimated to be between 2,000 and 10,000 years, but likely the former), but the exact nature and timing of their depopulation and eventual extinction remain an active research question. One aspect of Neanderthal lifeways which has recently brought attention to potential adaptations that could have impacted their survival is the nature of Neanderthal control, use, and maintenance of fire. Control, meaning hominin production of fire, is here distinguished from use, which can include the management of fire naturally occurring in landscapes to alter materials (Goldberg et al., 2017; Sandgathe et al., 2017; Stahlschmidt et al., 2020). The maintenance of fire additionally includes the curation of and different technologies which intersect with anthropogenic fire (i.e., heat-treatment of lithics; Goldberg et al., 2017; Sandgathe et al., 2017; Stahlschmidt et al., 2020). Due to fire acting as a mechanism to control one’s environment it has been suggested to be deeply linked to human’s evolutionary history and survival. Fire has been associated with many benefits, including the ability to cook, to preserve food, to modify wood and stone implements, to create birch tar, to offer protection from predators, to clear refuse, to create light, and to maintain a source of heat (Binford, 1978; Kozowyk et al., 2017, Sandgathe et al., 2011). Indeed, some researchers have proposed that fire use to increase caloric, and therefore energetic, returns through cooking could have contributed to the exponential increases in brain size seen 2 million years ago and again at ~400,000-500,000 years ago (Wrangham, 2009; Wrangham et al., 2017), while others have suggested that for migrations of hominins out of Africa, fire use would be necessary to survive in more northern latitudes (Gowlett, 2006). Despite these early predictions of fire’s importance, it is not reflected in the visible archaeological record (Roebrocks and Villa, 2011). Instead, the timing of habitual fire use in Europe, as predicted by more frequent presence of reputable fire evidence, is estimated to be ~400,000 years ago (Roebrocks and Villa, 2011). Neanderthal’s ability to make and have pyrotechnology was most starkly called into question when researchers noted patterns of fire absence, remarkably during relatively cold periods, at several occupational sites within a constrained geographical area that could not be described by post-depositional processes (Dibble et al., 2017; Sandgathe et al., 2011). This is despite these periods occurring well after 400,000 years ago, when anthropogenic fire is more commonly occurring (Roebrocks and Villa, 2011; Sandgathe et al., 2011). Therefore, the consideration of Neanderthal occupations without fire presents a few scenarios for researchers: 1) Neanderthals could be adapted to living without fire; 2) some Neanderthals could not make fire due to intellectual limitations or having lost the knowledge (through social learning); 3) Neanderthals in strained environmental conditions (i.e. limited fuel resources) did not always make fire or sparingly used fire as a resource, or 4) Neanderthals made fires elsewhere, potentially related to the organization of activities. As the absence of evidence presents a challenge to investigate further, this project instead addresses the ways in which Neanderthal combustion feature properties, when present, can be studied and described with faunal assemblages. I aim here to address with zooarchaeological analyses aspects of fire temperature, location, duration, and atmosphere which can contribute to greater knowledge of how Neanderthal populations utilized and curated fire. To achieve this goal, I use faunal remains to monitor changes which are induced by thermal alteration. Transformations to bone mineral are also demonstrated here by a large body of experimental studies, conducted as a sequence of collaborations to better understand the exact conditions under which bones are heated. I focus here on the chemical and structural changes to bone through spectroscopic analyses produced through Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray diffraction (XRD). These data support traditional zooarchaeological standards of heated bone categorization to recommend a holistic strategy for sampling and studying archaeological burnt bone. Chapter 2 introduces bone as a biomineral and presents a large experimentally produced referential dataset of bones heated from 100-1200 ˚C. FTIR and XRD are used here to demonstrate the changes in crystallite growth sizes, in addition to other aspects of thermal alteration. Bone which is charred and combusted (~ 300 ˚C) but has not yet experienced calcination (~700 ˚C) is demonstrated to be extremely porous with heightened solubility compared to both unburnt and calcined bone, and therefore it is vulnerable to differential preservation. The experimental bone is also compared to an archaeological assemblage of bone from the Upper Paleolithic (~30,000 years ago) site of Tolbor, Mongolia, to contextualize experimental observations and describe burning behaviors from an open air zooarchaeological assemblage. Chapter 3 isolates the variables of time and duration to better understand the heat induced changes to bone. In this study I specifically address the misleading nature of coloration as a primary indicator of high temperatures, as well as suggest criteria for discerning long-time durations within archaeological assemblages. This is particularly valuable because ethnoarchaeologically, duration time has been demonstrated to be connected to fire function and because natural grass fires are documented to primarily be rapid and ephemeral (Bellomo, 1993; Mallol et al., 2007; Mallol and Henry, 2017; Pyne et al., 1996; Scott, 2000). Eight experimental trials were conducted as a part of this experiment, heating bone to temperatures of 300˚, 550˚ and 750 ˚C for time durations of 10 minutes, 9 hours, and 48 hours. I describe bone in this study using coloration (Munsell color chart, 2010), FTIR, and XRD. Results indicate that bone can be depigmented and light in color at low temperatures for long durations, which is similar (and potentially misleading) to what is recognized as calcined bone heated at high temperatures. These bones exposed to low temperatures for long durations are not, however, structurally and chemically calcined, and the bioapatite crystallites and crystal lattice do not experience the growth or transformations that accompany high heat. This does positively indicate that bones burnt at low temperatures for long durations can be recognized in the archaeological record. Chapter 4 combines all observations from the experimental studies and applies this knowledge to the archaeological Middle Paleolithic (MP) faunal assemblage of Roc de Marsal (RDM) layer 9 from southwestern France. I utilize traditional zooarchaeological techniques alongside spectroscopic FTIR and mFTIR analyses on screened fragment and micromorphological thin sections to describe the properties of different Neanderthal fires within this depositional layer which have been previously described with lithic, geoarchaeological, and paleobotanical evidence (Aldeias et al., 2012; Goldberg et al., 2012; Reeves et al., 2019; Wroth et al., 2019). The abundance of thermally altered bone and well preserved combustion features in this layer provides an ideal environment to speak towards Neanderthal pyrotechnology. The burnt faunal assemblage of Roc de Marsal layer 9 and variability of burning conditions within that assemblage is consistent with differences between individual fires features inside the ancient dripline and those located in the cave exterior. This is a previously undescribed quality of fires at RDM, and the standardized methodology developed for this study can be used to address larger scale questions of Neanderthal fire use and curation with the future inclusion of additional assemblages. Chapter 5 provides directions for future research and concluding remarks.

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