Keywords:
1. Introduction
Bipedalism as preferential locomotor mode is considered essential in the hominins’ phylogenetic history (e.g., Darwin Citation1871; Harcourt-Smith and Aiello Citation2004; Fleagle and Lieberman Citation2015). However, simulating the locomotion of fossil species is usually a difficult challenge. On the one hand, as motion data are no accessible and soft tissues are not kept in the fossil record, functional inferences can only be based on osteological characteristics, such as body proportions, joint angles or the relative thickness of cortical bone (e.g., Lovejoy and Trinkaus Citation1980; Holliday Citation1997; Steudel-Numbers and Tilkens Citation2004; Ruff Citation2009). On the other hand, fossil osteological assemblages are most of the time very fragmentary (e.g., Wood and Lonergan Citation2008; Richmond and Hatala Citation2013), which complicates such inferences. Nevertheless, some fossil human taxa, such as Neandertals, appear sufficiently complete in order to undertake reliable biomechanical analyses of the musculoskeletal system (e.g., Chapman et al. Citation2010).
Here we report a study that aim at simulating the Neandertal gait from a specific plausible anatomical modelling and estimating the corresponding gait energy expenditure, focusing on methodological tasks.
2. Methods
2.1. Neandertal anatomical model
First, it was necessary to reconstruct a plausible anatomical model of the Neandertal locomotor system (including the pelvic girdle and both lower limbs) using available remains representing several individuals (). Indeed, although the Neandertals locomotor anatomy is relatively well known compared to other fossil taxa, no complete skeleton has been discovered so far so that we have a chimeric view of what the locomotor anatomy of Neandertals was (Sawyer and Maley Citation2005).
Figure 1. Methodological approach used in order to simulate walking and estimate associated energy costs.
The Neandertal anatomical model was based on the most complete Neandertal skeleton in our possession (La Ferrassie 1). Missing or fragmented anatomical parts of the lower limbs or pelvic girdle have been reconstructed from areas common to other morphologically close Neandertal bones (e.g., the coxal bone from Kebara 2, the right foot from La Ferrassie 2) after being scaled. When the material was too fragmentary to be able to completely reconstruct a bone, it was modelled from a mirror image from the same bone of different laterality. The re-articulation between different bones was carried out on the basis of our knowledge of the joint surfaces and spaces in anatomically modern humans and in accordance with the recommendations of the International Society of Biomechanics (Wu et al. Citation2002).
2.2. Simulation of Neandertal walk
This plausible anatomical model was used as input in a tool of simulation to generate a plausible Neandertal walk; this tool has previously been validated in current species (humans and other primates), based on the proportions of body segments and joint angles (Nicolas et al. Citation2009).
3. Results and discussion
Although our focus here is essentially methodological, the different possibilities of the reconstructions of the Neandertal locomotor system will be presented. The characteristics of the simulation will be detailed as well as the modifications made in order to adapt it to the fossilrecord.Biomechanical simulations and associated energy expenditures estimates, that are still in progress, will be detailed and confronted with the results obtained in anatomically modern humans in order to discuss whether the slight differences usually described in the locomotor anatomy of these two taxa result in functional differences.
4. Conclusions
This transversal study between biomechanics and paleoanthropology provides original information on the locomotor behavior of Neandertals, a key element in their evolution. From a methodological point of view, it also opens up access to similar studies for other fossil hominin taxa less well known than Neandertals.
Additional information
Funding
References
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