Serial reconstruction of Hominini manual phalanges

Serial morphology is the study of repeating, sequentially arranged structures in organisms, focusing on their development, organization, and evolutionary significance. Manual digits in primates, exhibiting proximodistal and radioulnar homology, can be analyzed using a serial morphological approach. This method offers a potential tool for reconstructing serial elements of hominin fossil record. Therefore, this study aims to analyze serial homology in proximal and intermediate phalanges of extant and extinct Hominini species to validate a novel methodology for reconstructing missing bones within the hand. For this purpose, we designed a template (27 true landmarks and 128 curve semilandmarks) for proximal and intermediate phalanges of digits II-V, applied to Homo sapiens (n = 125), Homo neanderthalensis (n = 9), Homo naledi (n = 9), Australopithecus sediba (n = 2), and Pan troglodytes (n = 122). Missing data were estimated using bilateral symmetry or geometric estimation methods. We used principal component analysis to quantify and examine morphological variability for each phalanx. Each serially reconstructed phalanx was validated by comparing the estimated to the original morphology using generalized Procrustes analysis and Procrustes distances, principal component analysis, and the Mann-Whitney U test. The results highlight both similarities and differences in serial homology between Pan and hominins, reflecting a shared developmental 'blueprint' alongside interspecific morphological variations influenced by genetic and functional factors. Finally, serial reconstruction with homologous elements is possible in the proximal and intermediate manual phalanges of Hominini, being more accurate with a proximal-proximal or intermediate-intermediate disposition, offering potential for reconstructing missing fossil hominin manual phalanges.