Retrodeformation of the Steinheim Cranium: Insights into the Evolution of Neanderthals

Abstract

A number of different approaches are currently available to digitally restore the symmetry of a specimen deformed by taphonomic processes. These tools include mirroring and retrodeformation to approximate the original shape of an object by symmetrisation. Retrodeformation has the potential to return a rather faithful representation of the original shape, but its power is limited by the availability of bilateral landmarks. A recent protocol proposed by Schlager and colleagues (2018) overcomes this issue by using bilateral landmarks and curves as well as semilandmarks. Here we applied this protocol to the Middle Pleistocene human cranium from Steinheim (Germany), the holotype of an abandoned species named Homo steinheimensis. The peculiar morphology of this fossil, associated with the taphonomic deformation of the entire cranium and the lack of a large portion of the right side of the face, has given rise to different hypotheses over its phylogenetic position. The reconstruction presented here sheds new light on the taphonomic origin of some features observed on this crucial specimen and results in a morphology consistent with its attribution to the Neanderthal lineage.

The Cranium I: Neurocranium

“…Moreover, the Steinheim cranium presents a more Neandertal‐derived suprainiac region and occipital torus, as well as a relatively elongated cranial vault when compared with the SH adult sample. Although the Steinheim cranium underwent plastic deformation, the new reconstruction indicates that the cranial height would probably be somewhat greater, but not as great as in SH (Buzi et al, 2021). In conclusion, the combination of cranial proportions and discrete traits, such as the morphology of the frontal torus or the occipital features, observed in the SH, are not found in any other African, European, or Asian MP individual.…”

A New Integrated Tool to Calculate and Map Bilateral Asymmetry on Three-Dimensional Digital Models

“…This, in turn, may have important consequences on the correct recognition of the phylogenetic position and taxonomy of the remains [22,23]. For instance, the 'roofed' appearance of the neurocranium in the Steinheim skull was interpreted as evidence of its plesiomorphic condition [46] but may be better indicative of taphonomic alteration [40] (Buzi et al, this volume). A similar misinterpretation might have complicated the interpretation of Ceprano Homo heidelbergensis calvarium [47].…”

“…We decided to test show.asymmetry on a highly deformed specimen before and after the retrodeformation procedure to see if the retrodeformed specimen shows a lower than expected level of asymmetry (as judged by comparison to living Homo sapiens specimens) and whether show.asymmetry captures this essential feature of the retrodeformation process. We used the Steinheim skull case-study presented in [40] (this volume). Steinheim cranium was found in 1933 in a gravel pit 70 km north of Steinheim an der Murr (Baden-Württemberg, Germany) and, despite a longstanding debate, is commonly attributed to Homo heidelbergensis, or otherwise linked to the Neanderthal lineage [41,42].…”

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

Special Issue “Symmetry in Human Evolution, from Biology to Behaviours”

“…Zhao et al [7] were interested in a regularly studied subject, the bilateral variations in the biomechanical properties of the humeri. However, they proposed a novel approach.…”