Variation in the Cranial Morphology of Hominin Specimens: Geographic Distinctions

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The Ohio State University

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Morphological variation has been widely used to identify differences between hominins and define their species. Despite this accumulated work, there is little consensus regarding the definition of most hominin species, which has significantly impacted our understanding of hominin relationships. Therefore, it is important to better contextualize the morphological variation seen among hominin fossil crania, to better understand species morphological boundaries and evaluate the significance of geographic dispersion within species. To explore hominin morphological variation, we collected 29 cranial linear measurements from 162 specimens from the literature. We excluded specimens and variables with more than 35% of missing values, resulting in 111 specimens and 17 measurements, divided into 15 species. The Homo species were further divided by geographic regions, resulting in 24 groups. We used linear discriminant analysis to explore morphological affinities among species and groups. The results show significant overlap between late Homo species irrespective of their geographic regions. Paranthropus and Australopithecus are distinct from late Homo, and H. habilis and rudolfensis occupy intermediary positions. The similarities in cranial morphological measurements observed within Homo across geographic boundaries support a greater need for broad species definition within the genus, with relatively small morphological changes among them. Nevertheless, Homo habilis and rudolfensis are clearly distinct from other Homo species, and our results support the separation of the Paranthropus and Australopithecus genera. These results are relevant to discuss the validity of species nomenclatures adopted in the past, given that over 70 different species names have been suggested for hominin fossils in the past.



Hominin, Morphology, Species, Variation, Evolution, Concept