Dimension scatter plot of blanks of tranchet blows (gray) and negatives of tranchet blows (black, only length and width) from Grotte de la Verpillière I.

<p>See data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188990#pone.0188990.s004" target="_blank">S4</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188990#pone.0188990.s005" target="_blank">S5</a> Tables.</p

Sequential steps necessary in the production sequence of <i>Keilmesser</i> with tranchet blow.

<p>Sequential steps necessary in the production sequence of <i>Keilmesser</i> with tranchet blow.</p

Comparison of working stage succession on all <i>Keilmesser</i> with tranchet blow from Grotte de la Verpillière I.

<p>Gray shaded field on top indicates the working stage succession which is prevalent at VP I and the gray shaded field below marks the main working stage succession at the Buhlen site (abbreviations: fl = flattening (surface shaping in general, green); tr = truncation (platform formation, blue); ef = edge formation (prevalently the formation of the active edge, violet); bc = backing (yellow); TB = performance of a tranchet blow (red); B = bottom side shaped first; T = top side shaped first and BT = indistinguishable if bottom or top side is shaped first).</p

<i>Keilmesser</i> with tranchet blow with cortical back.

<p><b>A</b> cortical blank is used as matrix, backing was not necessary (GER16.204-102.25.3).</p

<i>Keilmesser</i> with tranchet blow with cortical back.

<p><b>A</b> cortical blank is used as matrix, backing was not necessary (81.12.1.147).</p

The performance of tranchet blows at the Late Middle Paleolithic site of Grotte de la Verpillière I (Saône-et-Loire, France)

<div><p>This paper focuses on the technological characteristics of <i>Keilmesser</i> with a lateral tranchet blow modification on the cutting edge. It examines the underlying technological production of these bifacial objects: this implies the evaluation of their working stage succession, as well as produced forms necessary for the execution of tranchet blow performance. Furthermore, it offers a techno-morphological description of these enigmatic tools. The <i>Keilmesser</i> with tranchet blow and corresponding blanks of tranchet blows from Grotte de la Verpillière I in Germolles (Saône-et-Loire, France) are used as case study. The collection of <i>Keilmesser</i> with tranchet blow and corresponding blanks of tranchet blow has been massively expanded with new fieldwork and the review of ancient assemblages. The majority of the pieces were made on blanks from local raw material. The evaluation of the underlying production concept shows that a <i>Keilmesser</i> with tranchet blow, regardless of the wide range of morphologies and matrix size, always consists of specific parts that are necessary for the production sequence and the assumed function. The production of these pieces follows highly specific working stages, some of which can be interchanged in sequence. However, it is always the goal to obtain a low-angled cutting edge. The performance of a tranchet blow is not only an integral part of production, but it is rather the aim of the entire production.</p></div

Morphology change of <i>Keilmesser</i> with tranchet blow if broken or dull, and subsequently reworked and re-sharpened, after experimentally studies of Migal & Urbanowski [44] and observations of Jöris [32].

<p>Blue arrows indicate previous (dashed) and subsequent (solid) tranchet blows. Red squares and dashed arrows show the shift of morphological points on the outline. a) Parallel size reduction at active edge and bow, the subsequent tranchet blow is performed parallelly to the previous one; b) Inclined size reduction at active edge and bow resulting in an inclined direction of the subsequent tranchet blow; c) Reduction by repeated and parallel tranchet blow performance without any other reduction; d) Parallel size reduction and rotation for a new tranchet blow performance resulting in an opposing subsequent tranchet blow; e) Removal of the terminal part and parallel size reduction on active edge and bow resulting in a parallel subsequent tranchet blow.</p

Spatial distribution of <i>Keilmesser</i> with tranchet blow and blanks of tranchet blows at Grotte de la Verpillière I.

<p>a) Plan view of the rock shelter with evaluated positions of ancient trenches and exact positions of the new excavations (base data from cave floor plan measurements by Beutelspacher, Floss, Jantschke & Woerz, August 2–3, 2003, data use with permission of Floss). Blue shades or dots signal the position of blanks of tranchet blows and red shades or dots signal the position of KMTBs. Sharply delineated symbols represent objects from the Floss excavation. The amount is represented in the size of the symbol per square meter. Shaded areas represent objects from ancient excavations (and maybe surface collections) without exact localization. The exact quantity per activity is displayed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188990#pone.0188990.t001" target="_blank">Table 1</a>. The violet line indicates the position of the cross section shown below. b) Cross section of the rock shelter, collapsed rocks and the hillside in front of the rock shelter (GIS and three-dimensional reconstruction of both views: Hoyer).</p

<i>Keilmesser</i> with tranchet blow with late backing (GER15.204-104.1.6).

<p>A decorticated blank is used as matrix, backing is performed late in the working stage succession.</p

Degree differences of active edge angles before and after the tranchet blow performance on <i>Keilmesser</i> with tranchet blow (a) and blanks from tranchet blows (b) from Grotte de la Verpillière I.

<p>Degree differences of active edge angles before and after the tranchet blow performance on <i>Keilmesser</i> with tranchet blow (a) and blanks from tranchet blows (b) from Grotte de la Verpillière I.</p