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The bifacial Keilmesser is the type fossil of the late Middle Paleolithic Keilmessergruppen or Micoquian of central and eastern Europe. The tool is variable in shape but standardized regarding shaping sequences and morphological components. In this study we examine whether these components, a base and back opposite a sharp edge, are related only to bifacial tools or if they form a functional tool concept that was applied as well to simple edge retouched and to unifacially shaped flake tools. This study is based on a dataset of 29 3D-scanned artifacts from central Germany, for which the geographic origin, paleoenvironment, and chronological context are known in order to reduce variability introduced by these factors. With new luminescence dates, we can provide a chronological time frame for the collected and excavated artifacts to between 55 and 40 ka. We analyze variability caused by function, blank type, shaping, intensity of retouch, and typology, using 3D geometric morphometrics, Thickness Mapping, edge angle analysis, and multivariate principal component analysis based on conventional technological attributes and indices. We show that the unifacially shaped scrapers with a Keilmesser-like morphology can be classified as a unifacial variant of the bifacial Keilmesser. We interpret simple scrapers with a Keilmesser-like morphology as a special, simplistic variant of Keilmesser where the blank already fulfills the functional requirements of prehensile and active parts. With some caution related to sample size, an additional sample of Micoquian handaxes appears to be a related, but more symmetric tool concept in our data set.

The archaeological record represents a window onto the complex relationship between stone artefact variance and hominin behaviour. Differences in the shapes and sizes of stone flakes-the most abundant remains of past behaviours for much of human evolutionary history-may be underpinned by variation in a range of different environmental and behavioural factors. Controlled flake production experiments have drawn inferences between flake platform preparation behaviours, which have thus far been approximated by linear measurements, and different aspects of overall stone flake variability (Dibble and Rezek J Archaeol Sci 36:1945-1954 Lin et al. Am Antiq 724-745, 2013; Magnani et al. J Archaeol Sci 46:37-49, 2014; Rezek et al. J Archaeol Sci 38:1346-1359, 2011. However, when the results are applied to archaeological assemblages, there remains a substantial amount of unexplained variability. It is unclear whether this disparity between explanatory models and archaeological data is a result of measurement error on certain key variables, whether traditional analyses are somehow a general limiting factor, or whether there are additional flake shape and size drivers that remain unaccounted for. To try and circumvent these issues, here, we describe a shape analysis approach to assessing stone flake variability including a newly developed three-dimensional geometric morphometric method ('3DGM'). We use 3DGM to demonstrate that a relationship between platform and flake body governs flake shape and size variability. Contingently, we show that by using this 3DGM approach, we can use flake platform attributes to both (1) make fairly accurate stone flake size predictions and (2) make relatively detailed predictions of stone flake shape. Whether conscious or instinctive, an understanding of this geometric relationship would have been critical to past knappers effectively controlling the production of desired stone flakes. However, despite being able to holistically and accurately incorporate three-dimensional flake variance into our analyses, the behavioural drivers of this variance remain elusive.

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The Willandra Lakes complex is one of the few locations in semi-arid Australia to preserve both paleoenvironmental and Paleolithic archeological archives at high resolution. The stratigraphy of transverse lunette dunes on the lakes’ downwind margins record a late Quaternary sequence of wetting and drying. Within the Willandra system, the Lake Mungo lunette is best known for its preservation of the world’s oldest known ritual burials, and high densities of archeological traces documenting human adaptation to changing environmental conditions over the last 45 ka. Here we identify evidence at Lake Mungo for a previously unrecognised short-lived, very high lake filling phase at 24 ka, just prior to the Last Glacial Maximum. Mega-lake Mungo was up to 5 m deeper than preceding or subsequent lake full events and represented a lake volume increase of almost 250%. Lake Mungo was linked with neighboring Lake Leaghur at two overflow points, creating an island from the northern part of the Mungo lunette. This event was most likely caused by a pulse of high catchment rainfall and runoff, combined with neotectonic activity which may have warped the lake basin. It indicates a non-linear transition to more arid ice age conditions. The mega-lake restricted mobility for people living in the area, yet archeological traces indicate that humans rapidly adapted to the new conditions. People repeatedly visited the island, transporting stone tools across water and exploiting food resources stranded there. They either swam or used watercraft to facilitate access to the island and across the lake. Since there is no evidence for watercraft use in Australia between initial colonization of the continent prior to 45 ka and the mid-Holocene, repeated visits to the island may represent a resurrection of waterfaring technologies following a hiatus of at least 20 ky.

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Studies have long noted the influence of stone package size and reduction intensity on lithic assemblage composition, particularly in the form of flake size distributions. However, it remains difficult to distinguish objectively the effect of either factor in archaeological contexts without controlling for the variation in one of the two variables. Here we report on an experimental study designed to test the null hypotheses that original stone size and reduction intensity have no impact on the size distribution of lithic flake debris produced during core reduction. Results indicate statistically significant influence from original stone size but not reduction intensity, although the effects from the former are low enough to be considered trivial. In reviewing a sequence of archaeological assemblages from a Middle Paleolithic site, all exhibit an excess of smallsized materials in comparison to the experimental data. When exceptionally high frequencies of the smaller size classes occur, taphonomic processes are clearly responsible.

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