*2.3. Data Preparation*

We acquired 50 anatomical landmarks on each modern human skull specimen on the entire cranial surface (e.g., facial complex, neurocranium, and cranial base). We placed 500 equidistant surface semilandmarks on the left side only of a reference sample. We slid the semilandmark on the entire sample of 20 specimens following the protocol included in 'Morpho' [32]. Then, we mirrored the slid configurations to the other side and projected them on the surfaces after a GPA step rotating semilandmark configuration accordingly to the set of bilateral landmarks.

Concerning fossil specimens, we manually sampled bilateral landmarks on Petralona and Saccopastore by using Amira software (version 5.4.5 [43]) (see Supplementary Materials for the full detailed description of landmarks). We created decimated patches by cutting half of the skull, and then we removed the damaged parts on each surface (i.e., the browridge region from Saccopastore 1). For each patch, we retrieved the coordinates of the vertices and used them as semilandmarks. As we needed bilateral points, we symmetrized the semilandmarks on the opposite side and slid them along the surface by using manually placed landmarks as a reference. The manipulation of landmarks and semilandmarks was performed by using the R Cran software (version 4.0.5).

For the Steinheim case study, we used both the original and the retrodeformed patches from the study presented in [40] (this volume).
