Cladistics with geometric morphometric data: the variability of the calvarium in the genus Homo

Over the last 30 years, several protocols to adapt 3D geometric morphometric data to cladistics have been developed. Strongly criticised, these protocols are only occasionally used in palaeoanthropology, despite the obvious heuristic potential of such an approach. This study tests two different protocols to analyse 23 operational taxonomic units (OTUs) representing the genera Pongo, Gorilla, Pan, Australopithecus and Homo, in order to evaluate the phylogenetic information derived from geometric morphometric data. The 23 OTUs were based on averaged Procrustes-aligned coordinates (generalised Procrustes analysis) of three landmark configurations (148, 347 and 636 landmarks) describing the calvarium morphology of 78 specimens. The first protocol used the coordinates of the principal components, obtained after a principal component analysis, as variables describing the OTUs. The second approach directly used the aligned 3D coordinates of the landmarks. These two datasets were then analysed with both the heuristic and branch-and-bound algorithms implemented in the TNT software. These analyses produced a unique cladistic tree for each dataset. Independent of the matrix used to obtain the trees, these preliminary results were phylogenetically consistent and support debated paleoanthropological hypotheses.