Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04–1.95 million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.
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New fossils from Kromdraai and Drimolen, South Africa, and their distinctiveness among Paranthropus robustus
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All data are available in the Methods, Supplementary Information and at MorphoBank (http://morphobank.org/permalink/?P3477). Specimen DNH 155 is curated by the Evolutionary Studies Institute of the University of the Witwatersrand. Requests for permission to examine DNH 155 should be directed to their hominin access committee and are subject to regulations of the South African Heritage Resources Agency.
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We thank Y. Rak and B. Kimbel, who are completing a detailed description of the DNH 7 skull, for sharing observations and insights on this specimen, a number of which correspond to ours; however, endorsement of our conclusions is not implied and all observations and interpretations are, of course, our own. The research underpinning this publication was undertaken while J.M.M. and A.B.L. were completing a PhD at La Trobe University. We thank the student excavators from the Washington University Drimolen Cave Field School and the Australian Palaeoanthropological Fieldschool at Drimolen. We dedicate the discovery of DNH 155 to I. Good, whose daughter S. Good uncovered the specimen on Father’s Day in 2018. We thank R. Nsibande for invaluable logistical assistance and we remember S. Mokobane for many years of similar support as well as mentorship and friendship but who sadly died mere months before the discovery of DNH 155. We thank J. Massey for providing access to digital data, K. McNulty and A. Gordon for providing statistical advice and support, A. Larson for advice regarding species concepts and to J.-J. Hublin and P. Gunz for access to data and support. We thank D. Wright for methodological assistance with the tip-dated analysis. We thank J. Adams and M. Meredith-Williams for the supervision provided to J.M.M. and A.B.L. throughout their PhD programmes (in addition to that also provided by A.I.R.H. and D.S.S.). We also thank P. Strait for timely advice regarding probability theory. We thank the landowners (K. and N. Nkosi) for their continuing support to excavate at Drimolen, including through South African Heritage Resource Agency permit nos. 2597 and 2883 to S.E.B. and A.I.R.H. This research was funded and supported by Higher Degree Research fee waivers and living scholarships from La Trobe University to J.M.M. and A.B.L. and an Australian Research Council Discovery Grant no. DP170100056 to A.I.R.H. and D.S.S. Biomechanical analysis was supported by a grant to D.S.S. from the Biological Anthropology Directorate of the National Science Foundation (no. NSF-BCS-0725126). S.N. was supported by the Max Planck Society.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Specimen positioned in a, posterior, b, basal, and c, right lateral views. Scale bar = 10mm.
Right lateral views of P. robustus specimens a, DNH 7, c, SK 48, e, SK 52, f, SKW11, and g, SK 12. Left lateral views of b, DNH 155, and d, TM 1517. Vertical red lines pass through P4/M1 on each specimen. The anterior aspect of the root is positioned at this line in a and b but anterior to the line in c–g. Scale bar = 10mm.
Paranthropus robustus specimens shown slightly offset from palatal view in order to visualize the lateral wall of the maxilla. a, DNH 7. b, DNH 155. c, SK 12. d, TM 1517. e, SK 48. All specimens are scaled to the same P4 – M2 length. Red and yellow lines represent the anterior- and posterior-most aspects of the zygomatic root on the maxilla. The root is proportionally thinnest in DNH 7 and DNH 155.
Oblique views of P. robustus specimens a, DNH 155, b, DNH 7, c, SK 46, d, SK 12, e, SK 52, f, TM 1517, and g, SK 48. Arrows indicate change of contour between the surfaces of the zygomatic bone and maxillary trigon. Shading indicates that the change in contour is abrupt and coincident with the zygomaticomaxillary suture in c–g, In a and b the change in contour is gentle (brackets) and positioned above the suture such that the suture lies within the trigon as opposed to being its superolateral margin. Scale bar = 10mm.
Frontal views of P. robustus specimens a, DNH 152, b, DNH 7, c, DNH 155, d, SK 46, and e, SK 48. Arrows indicate a squared supraorbital corner associated with a roughly horizontal supraorbital torus in d and e. In a and b the homologous region of the orbital margin is rounded, and in c the corner is not squared and the supraorbital torus is inclined. Note that specimen SK 46 is badly distorted, but the torus and corner are locally undistorted. Images not to the same scale.
Principal component analysis of 19 scale-adjusted craniofacial dimensions (Supplementary Data) were performed on chimpanzees (green) and fossil hominins (P. robustus = red, P. boisei = orange, Au. africanus = blue, early Homo = black) in order to convert the morphometric data into statistically independent variables to be used as input for cluster analysis. a, Plot of PC1 vs. PC2. b, PC3 vs. PC 4. PC 1 accounts for 34.5% of the total variance, PC2 for 28.5%, PC3 for 8.5%, and PC4 for 7.6%. PC1 and PC4 reflect interactions between facial height and minimum frontal breadth, albeit in inverse ways (PC1 loadings: Scale-adjusted Superior Facial Height = -0.51, Scale-Adjusted Nasal Height = -0.43, Scale-Adjusted Minimum Frontal Breadth = 0.44; PC4 loadings: Scale-adjusted Superior Facial Height = 0.41, Scale-Adjusted Minimum Frontal Breadth = 0.49). PC2 reflects palate shape (PC2 loadings: Scale-adjusted Outer Alveolar Breadth = -0.41, Scale-adjusted Interalveolar Distance at P3 = 0.43). PC3 reflects alveolar shape (PC3 loadings: Scale-adjusted Alveolar Height = 0.39, Scale-adjusted Maxilloalveolar length = 0.41). c, Dendrogram of UPGMA of the 19 sets of component scores (accounting for 100% of the total variance) showing that DNH 155 clusters with DNH 7 within P. robustus and Paranthropus clusters.
Frontal (top row), lateral (middle row) and superior-oblique (bottom row) views of a, c, e, DNH 7 and b, d, f, DNH 155. Note that the face of DNH 7 is detached from the specimen’s neurocranium and neurocranial distortion makes it difficult to join the two pieces. The placement of the face on the neurocranium in lateral and oblique views is heuristic and no morphological assessments reported here are dependent on these cranial parts being properly aligned. Moreover, the lateral view of DNH 7 is a reflected image of the specimen’s right side. DNH 155 is absolutely larger than DNH 7, it exhibits a sagittal crest (red arrows) and strong anteromedial incursion of the superior temporal lines (yellow arrows), and a zygomatic body that projects anterior to the nasal aperture (green arrow). DNH 7 is smaller, it lacks a sagittal crest, has only moderate anteromedial incursion of the superior temporal lines, and its zygomatic body does not project anterior to the nasal aperture. Scale bar = 10mm. Oblique views not to scale.
Buccolingual breadth vs. mesiodistal length of P. robustus postcanine teeth at Drimolen and Swartkrans. a, P3. b, P4. c, M1. d, M2. e, M3. Values for specimen DNH 155 are corrected for interproximal wear.
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Martin, J.M., Leece, A.B., Neubauer, S. et al. Drimolen cranium DNH 155 documents microevolution in an early hominin species. Nat Ecol Evol 5, 38–45 (2021). https://doi.org/10.1038/s41559-020-01319-6
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