The use of Z-scores to facilitate morphometric comparisons between African Plio-Pleistocene hominin fossils: An example of method

• Published in: South African Journal of Science 2022-01, Vol.118 (1-2), p.91-95
• Main Authors: Thackeray, J. Francis, Kullmer, Ottmar
• Format: Article
• Language: English
• Subjects: Australopithecus; Cranium; Fossils; Genetic variability; Hominids; Hominin; Homo habilis; Mandible; Mathematical analysis; Methods; Morphology; Morphometrics; Pleistocene; Plio-Pleistocene; PlioPleistocene; Reference materials; Skull; Standard error; Statistics; Taxonomy; Variability; Variation
• ISSN: 0038-2353; 1996-7489
• DOI: 10.17159/sajs.2022/11182

South Africa and East Africa each have a rich palaeoanthropological heritage, but the taxonomy of fossil hominins from these regions is controversial. In this study, two morphometric methods related to the quantification of variability in morphology have been applied to pairwise comparisons of linear measurements of hominoid crania and mandibles. The log-transformed standard error of the m-coefficient ('log sem') is calculated from linear regressions. Like Procrustes Distances (PD), log sem statistics can serve to quantify variation in the shape of a cranium or mandible in the context of a constellation of landmarks. In this study, PD and log sem statistics are integrated and standardised using Z-scores, and applied probabilistically to Plio-Pleistocene hominins. As a test case, OH 7 and OH 24 as reference specimens of Homo habilis are compared to fossils representing other taxa. There is a wide spectrum of variation in Z-scores for specimens attributed to early Homo dated within the period between circa 1.8 Ma and 2 Ma. In terms of morphometric variation predating 1.8 Ma, Z-scores (Z