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Poster De Conférence Année : 2022

From footprint morphometrics to the stature of fossil hominins: experimental regressions and uncertainties

Résumé

Hominin footprints provide access not only to the locomotor behaviours of fossil taxa but also to their body characteristics such as their stature. Stature is usually estimated from the length of footprints by using the well-known foot length to stature ratio (15%). However, the morphology of the footprints is not only impacted by the dimensions of the foot but also by the biomechanical features of the individuals and the nature of the substrate in which they were left. Therefore, recent studies emphasize the need to better understand the relationships between individual stature and footprint morphometry and not just foot morphometry. Furthermore, while stature estimates have been based solely on linear measurements, methodological advances in 3D scanning and geometric morphometrics offer the possibility of investigating the correlation of stature with a wide range of under-exploited morphometric variables. It is in this context that this study aims to quantify the relationships between different morphometric variables measured on footprints and individual stature by means of an experimental study and to discuss the application of these relationships to the fossil record. In order to carry out this study, 22 individuals aged between 10 and 36 years and for which their stature was measured, were asked to make footprints on an experimental area. This area is composed of a dune sand of fine granulometry. This type of sediment is common in the fossil record and induces by its grain size, porosity and moisture a high intra-individual variability impacting the uncertainty of biological estimates from footprints. Each individual moved on the area in different ways (static position, habitual walking, slow running). A total of 221 experimental footprints, including 58 footprints digitized in 3D by photogrammetry, were thus studied by measuring 24 morphometric variables (16 linear, 5 surface and 3 volume measurements). The correlation between each variable and the stature of the individuals was then investigated. The linear measurements of the footprints show on average higher correlations with stature than the surface and especially the volume measurements, the volume of the footprint being strongly impacted by the substrate moisture. The footprint lengths measured from the base of the heel to the tip of the hallux and second toe are the dimensions most correlated with stature, linear regressions giving the best predictions. It should be noted, however, that although these dimensions have one of the lowest intraindividual variability of the 24 morphometric variables, this variability remains significant. Indeed, the length of a footprint can differ by more than 10% from the average length of footprints made by a single individual. This uncertainty must be considered in particular for the study of isolated fossil footprints for which it is impossible to quantify intra-individual dispersion in the absence of trackways. The estimation of stature from footprints is therefore confronted with two types of uncertainties, that of regressions between the average footprint length and the stature of the individuals and the more important uncertainty linked to the substrate deformation inducing intraindividual variability. In addition to these two uncertainties, there is a third uncertainty related to the variations in body proportions during hominin evolution. Indeed, the ratio between foot size and stature probably differ between modern populations and fossil taxa. However, direct quantification of this ratio is impossible for fossil species, including the most recent ones such as Neandertals, because of the fragmentary aspect of the fossil record.
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Dates et versions

hal-03802103 , version 1 (06-10-2022)

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  • HAL Id : hal-03802103 , version 1

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Jérémy Duveau. From footprint morphometrics to the stature of fossil hominins: experimental regressions and uncertainties. 12th European Society for the study of Human Evolution meeting, Sep 2022, Tübingen, Germany. 2022. ⟨hal-03802103⟩
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