Skull diversity in the Homo lineage and the relative position of Homo naledi.
The discovery of Homo naledi has expanded the range of phenotypic variation in Homo, leading to new questions surrounding the mosaic nature of morphological evolution. Though currently undated, its unique morphological pattern and possible phylogenetic relationships to other hominin taxa suggest a complex evolutionary scenario. Here, we perform geometric morphometric analyses on H. naledi cranial and mandibular remains to investigate its morphological relationship with species of Homo and Australopithecus. We use Generalized Procrustes analysis to place H. naledi within the pattern of known hominin skull diversity, distributions of Procrustes distances among individuals to compare H. naledi and Homo erectus, and neighbor joining trees to investigate the potential phenetic relationships between groups. Our goal is to address a set of hypotheses relating to the uniqueness of H. naledi, its affinity with H. erectus, and the age of the fossils based on skull morphology. Our results indicate that, cranially, H. naledi aligns with members of the genus Homo, with closest affiliations to H. erectus. The mandibular results are less clear; H. naledi closely associates with a number of taxa, including some australopiths. However, results also show that although H. naledi shares similarities with H. erectus, some distances from this taxon - especially small-brained members of this taxon - are extreme. The neighbor joining trees place H. naledi firmly within Homo. The trees based on cranial morphology again indicate a close relationship between H. naledi and H. erectus, whereas the mandibular tree places H. naledi closer to basal Homo, suggesting a deeper antiquity. Altogether, these results emphasize the unique combination of features (H. erectus-like cranium, less derived mandible) defining H. naledi. Our results also highlight the variability within Homo, calling for a greater focus on the cause of this variability, and emphasizing the importance of using the total morphological package for species diagnoses.
Department of Archaeology, University of Cape Town, Rondebosch 7701, South Africa; Department of Anthropology, University at Buffalo, SUNY, Buffalo, NY 14261, USA; Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Human Evolution Research Institute, University of Cape Town, Rondebosch 7701, South Africa. Electronic address: lschroeder1510@gmail.com.
Lauren
L
Schroeder
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Anthropology, The University of Iowa, Iowa City, IA 52242, USA; Department of Sociology and Anthropology, Metropolitan State University of Denver, CO 80217, USA.
Jill E
JE
Scott
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Applied Forensic Sciences, Mercyhurst University, Erie, PA 16546, USA; Department of Anthropology/Archaeology, Mercyhurst University, Erie, PA 16546, USA.
Heather M
HM
Garvin
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.
Myra F
MF
Laird
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Human Evolutionary Studies Program and Department of Archaeology, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada.
Mana
M
Dembo
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Geology and Paleontology, Croatian Natural History Museum, Demetrova 1, 10000 Zagreb, Croatia.
Davorka
D
Radovčić
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.
Lee R
LR
Berger
Evolutionary Studies Institute and Centre for Excellence in PaleoSciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa; Department of Anthropology, Texas A&M University, College Station, TX 77843, USA.
Darryl J
DJ
de Ruiter
Department of Archaeology, University of Cape Town, Rondebosch 7701, South Africa; Human Evolution Research Institute, University of Cape Town, Rondebosch 7701, South Africa. Electronic address: becky.ackermann@uct.ac.za.
Rebecca R
RR
Ackermann
D000818:Animals; D005075:Biological Evolution; D005580:Fossils / Q000033:anatomy & histology*; D015186:Hominidae / Q000033:anatomy & histology*; D008334:Mandible / Q000033:anatomy & histology*; D010802:Phylogeny; D012886:Skull / Q000033:anatomy & histology*; D013019:South Africa
Cranial and mandibular variation; Dinaledi hominins; Genus Homo; Geometric morphometrics; Homo erectus; Rising Star