Model-based inferring of Neanderthal upper cervical spine motion

The primary aim of this pilot study is not to provide definitive statements on Neanderthal kinematics, but rather to illustrate the potential of Procrustes Motion Analysis (PMA) combined with predictive modelling as a robust tool for addressing questions of functional morphology in the fossil record. We use this novel approach to model and compare the potential upper cervical spine (UCS) flexion-extension kinematics of the La Ferrassie 1 Neanderthal and modern humans. The study material comprised the 3D virtual morphology of the occipital base, atlas (C1), and axis (C2) of La Ferrassie 1 and the corresponding kinematic and morphological data from seven unembalmed modern human cadaveric specimens. We first used the PMA framework to analyze the shape-motion relationship in the modern human sample. This relationship was then used to build a predictive model. We applied this model to the UCS morphology of La Ferrassie 1-inferring its potential motion trajectory rather than measuring direct fossil kinematics-and statistically compared the results to the modern human mean. Contrary to previous hypotheses based solely on morphological inference, our model-based results challenge the assumption of reduced Neanderthal neck mobility. The inferred trajectory of flexion-extension for La Ferrassie 1 were statistically comparable to that of the modern human sample, suggesting no significant difference in this specific movement. This study demonstrates the utility of integrating empirical motion data, geometric morphometrics, and predictive modelling in paleoanthropology, offering a significant advance over traditional morphological inference. By successfully illustrating the application of PMA, this research provides a new framework for investigating hominin kinematics, while simultaneously emphasizing that the kinematics presented for the Neanderthal specimen were predicted and modelled, not directly measured.