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Postcranial evidence of late Miocene hominin bipedalism in Chad

Abstract

Bipedal locomotion is one of the key adaptations that define the hominin clade. Evidence of bipedalism is known from postcranial remains of late Miocene hominins as early as 6 million years ago (Ma) in eastern Africa1,2,3,4. Bipedality of Sahelanthropus tchadensis was hitherto inferred about 7 Ma in central Africa (Chad) based on cranial evidence5,6,7. Here we present postcranial evidence of the locomotor behaviour of S.tchadensis, with new insights into bipedalism at the early stage of hominin evolutionary history. The original material was discovered at locality TM 266 of the Toros-Ménalla fossiliferous area and consists of one left femur and two, right and left, ulnae. The morphology of the femur is most parsimonious with habitual bipedality, and the ulnae preserve evidence of substantial arboreal behaviour. Taken together, these findings suggest that hominins were already bipeds at around 7 Ma but also suggest that arboreal clambering was probably a significant part of their locomotor repertoire.

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Fig. 1: The femur of S. tchadensis.
Fig. 2: Comparative analysis of the subtrochanteric and midshaft cross-sectional contours of the TM 266 femur.
Fig. 3: Comparison of cortical thickness distributions between S.tchadensis and extant great apes.
Fig. 4: Ulnar remains of S.tchadensis.

Data availability

The postcranial material from Chad is curated and conserved by the CNRD in Chad. Access to the palaeontological material collected by the MPFT is regulated by formal agreement between the Université de N’Djamena, the CNRD and the Université de Poitiers and is available for study upon approval from Chad authorities. Access to the material for loan and/or study of the material, including original 3D microtomographic data, is available upon request to the CNRD, service de paléontologie, at nekoulnanc@yahoo.fr. Data supporting the findings of this study are available within the paper and its supplementary information files.

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Acknowledgements

We thank the following institutions and colleagues: the Chadian Ministère de l’Enseignement Supérieur, de la Recherche Scientifique et de l’Innovation and the Centre National de Recherche pour le développement (CNRD); the University of N’Djaména, the University of Poitiers, the Centre National de la Recherche Scientifique (CNRS), the French Ministère de l’Europe et des affaires étrangères, the Embassy of France to Chad, the région Nouvelle Aquitaine (project AH-HEM, NA2018-195586), and the French Army (MAM, Épervier and Barkhane) for its logistical support; M. Y. Khayal and B. Mallah (Director of the CNRD); all the MPFT members who participated in the field research, in particular D. Ahounta, G. Fanoné (deceased), A. Mahamat, F. Lihoreau and J. Surault; M. Brunet, head of the MPFT, for initiating this work and gathering the first comparative data as the basis of the present manuscript; the Musée Royal d’Afrique Centrale at Tervuren (E. Gillissen), the National Museum of Ethiopia, the National Museums of Kenya, Universitair Ziekenhuis at Leuven (W. Coudyzer), University of the Witwatersrand, B. Asfaw (Rift Valley Research Service), Y. Haile-Selassie (Cleveland Museum of Natural History), D. Johanson and W. Kimbel (Institute of Human Origins and Arizona State University at Tempe), C. O. Lovejoy (Kent State University), M. G. Leakey and R. Leakey, D. Pilbeam (Peabody Museum and Harvard University), T. D. White (University of California at Berkeley) and G. Suwa (University Museum of Tokyo) who granted M. Brunet and us access to their collections and contributed to the field research that collected these specimens; B. Zipfel (University of the Witwatersrand) for facilitating access to the hominin material from South Africa, including the StW 573m femur; G. Berillon, J. Braga, K. Carlson, R. Clarke, Q. Cosnefroy, R. Crompton, J. Heaton, J. Kappelman, D. Lieberman, F. Marchal, M. Pina, D. Stratford and M. Tocheri for providing comparative data and valuable comments; B. Senut, M. Pickford and D. Gommery for stimulating discussions and granting access to the CT scan and cast material of O.tugenensis; the Orrorin CT scans were done at the Clinique Pasteur (J.-P. Deymier, F. Berthoumieu, G. Larrouy, S. Charreau, A. M'Voto and P. Roch); the Orrorin Community Organisation and the Kenya Ministry of Education, Science and Technology; K. Cheboi and the Tugen palaeontology field team; all our colleagues and friends for their help and discussion, in particular D. Barboni, A. Mazurier (Plateforme Platina, IC2MP), A. Novello, O. Chavasseau, G. Merceron and J. Surault; S. Riffaut, J. Surault and X. Valentin for technical support; and G. Florent, C. Noël, G. Reynaud, C. Baron, M. Pourade and L. Painault for administrative guidance. Funding was provided by PALEVOPRIM and project AH-HEM (NA2018-195586).

Author information

Authors and Affiliations

Authors

Contributions

F.G. and G.D. contributed equally to this work and are both first authors. F.G. and G.D. designed the study, collected and interpreted the data, ran the analyses and interpreted the results. G.D., F.G. and J.-R.B. wrote the manuscript. G.D., F.G., J.-R.B., L.P., H.T.M., A.L., A.M., P.V. and N.D.C. discussed the results and revised earlier drafts of the paper.

Corresponding author

Correspondence to F. Guy.

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Extended data figures and tables

Extended Data Fig. 1 Photographs of the postcranial original material from Toros-Ménalla, Chad.

TM 266-01-063 femur: a, anterior view; b, posterior view; c, lateral view; d, medial view. TM 266-01-358 ulna: e, anterior view; f, posterior view; g, lateral view; h, medial view. TM 266- 01-050 ulna: i, anterior view; j, posterior view; k, lateral view; l, medial view. Scale bar 10 mm.

Extended Data Fig. 2 Femoral anterior curvature.

Panel a. comparative femoral anteroposterior curvature. The TM 266-01-063 femur (S. tchadensis) is compared (from left to right) to BAR 1002’00 (Or. tugenensis, as published in2,84), BAR 1002’00 (Or. tugenensis, acquired from CT-scan data, as published in52), BAR 1003’00 (Or. tugenensis, acquired from CT-scan data, courtesy of B. Senut, M. Pickford and D. Gommery), StW 573 (A. prometheus, as published in10) and A.L. 288-1p (A. afarensis, cast). Femora are in medial view. The colored portions for TM 266-01-063, BAR 1002’00, BAR 1003’00 and StW 573 illustrate the interval used for the 2D geometric morphometrics analysis of the femoral antero-posterior curvature (between 80% and 35% of the biomechanical femoral length, this study). Two version of Or. tugenensis anterior femoral curvature were included in the analysis, BAR 1002’00* (Or. tugenensis, as published in2,84), and BAR 1002’00** (Or. tugenensis, acquired from CT-scan data, as appears in52). Femora are about the same scale. Ant. for anterior, dist. for distal. Panel b. Comparative analysis of the anterior femoral curvature of the TM 266 specimen. Principal component analysis of Procrustes coordinates for the anterior femoral curvature, in medial view, as estimated between 80% and 35% of the femoral biomechanical length in fossil and extant hominoids. Bivariate plot of PC1 and PC2 summarizes 89.3% of the total variation. Anterior femoral curvature variation, summarized by the PC1-2 shape space, is illustrated by an outline representation at the extremity of each axis; the red dot is for the proximal end of the anterior contour. Black solid arrows mark the main anterior convexities, whereas white open arrows are for the main anterior concavities. Two version of Or. tugenensis anterior femoral curvature were included in the analysis, BAR 1002’00* (Or. tugenensis, as published in2,84), and BAR 1002’00** (Or. tugenensis, acquired from CT-scan data, as appears in52). Distribution of the specimens along PC1 describes the degree of curvature between two morphological femoral shapes; rectilinear (negative values) and anteriorly curved (positive values). Along PC2, distribution of the specimens illustrates additional aspects of the femoral curvature including a transition between proximally (negative values) to distally (positive values) located anterior curvature. Along PC1, extant apes describes a morphological gradient from straight femora in orangs to curved femora in gorilla, chimpanzee and humans being intermediates. Along PC2, humans, gorillas and orangutans present a proximally located anterior curvature while chimpanzees display a relatively more distal anterior curvature. In this pattern, the fossil hominins, apart from BAR 1002’00** and early Homo, occupy a central position in the morphospace in having moderately curved femora and a centrally located anterior curvature. TM 266-01-063 presents higher degree of curvature compared to other fossil hominins, within the range of chimpanzees and gorillas along PC1 but close to BAR 1002’00*. Alternative version of BAR 1002’00** falls out of the range of variation for the extant apes in having a relatively straight femoral shaft, clearly differing in this respect from BAR 1002’00*. BAR 1002’00** is in line with early Homo along PC1 and is overall closer to KNM-ER 1481 than any other apes.

Extended Data Fig. 3 Comparison of TM 266-01-063 with extant African apes and Or. tugenensis, illustrating femoral size variation.

From left to right: femoral specimens of Gorilla, Pan, Homo, TM 266-01-063, BAR 1003’00, BAR 1002’00. All femora are in posterior view. Scale bar is 50 mm.

Extended Data Fig. 4 Illustration and estimation of the TM 266-01-063 diaphyseal antetorsion.

a. 3D view of the femur (virtual model) showing the position of the proximal (base of the lesser trochanter) and distal (25% of the total biomechanical length) transverse sections; b. transverse CT-slice cross-sections showing the mediolateral axis (M-L) and the orientation of the longest axis of the diaphyseal sections (proximal, upper panel and distal, lower panel) assessed by the mean of Feret’s diameters (Ft1 and Ft2 respectively); c., 3D view of the femur (virtual model) showing the femoral antetorsion by the mean of the relative orientation of the proximal and distal Feret’s diameters. The white curved arrows mark the diaphyseal torsion angle (DT) measured between Ft1 and Ft2. Ft1: 11.7° counterclockwise, relative to mediolateral axis; Ft2: 153.2° counterclockwise, relative to mediolateral axis; DT is 38.5°. The right panel d presents an illustration of the variation of the parameter DT, in degrees, in chimpanzee, gorilla and modern human. Box and whiskers are for mean (centre), mean ± standard deviation (bounds of box) and minimum/maximum (whiskers). In chimpanzee means for P. paniscus (Pp, n = 6) and Pan troglodytes (Pt, n = 12) are given. The red dotted line corresponds at the value measured for TM 266-01-063.

Extended Data Fig. 5 Bivariate plot of PC1 (33.8%) versus centroid size (Cs).

The Cs mean (symbols are for group mean) and its range (whiskers) for the extant and extinct hominoid sample are provided in the left grey panel. Modern humans, n = 12; bonobos, n = 12; common chimpanzees, n = 18; gorillas, n = 9; orangutans, n = 7; fossil hominins, n = 10 (80%), n = 13 (50%); Miocene apes, n = 3.

Extended Data Fig. 6 Cortical bone variation of TM 266-01-063.

Panels a, b, c. Cross-sectional geometric properties of the TM 266-01-063 femur. a, Location of transverse microCT-slices at the distal margin of the lesser trochanter (1) and at standard levels of biomechanical length (2-5). Corresponding percent of cortical area (i.e., CA/TA*100) is given at 80%, 65%, 50% and 35%; b, microCT-slice images of the selected transverse sections; c, interpretive drawings of the cortical thickness for selected microCT-slice sections, numbers are for the measured cortical thickness anteriorly, posteriorly, medially and laterally (in mm), maximum thickness is in red while minimum thickness is in green. TA, total area in mm2; CA, cortical area in mm2; %, percent of cortical area. Med. is for medial and Lat. is for lateral. Scale bar is (a) 10 mm; (b) 6 mm. Panel d. Three-dimensional cortical thickness of TM 266-01-063. From left to right, anterior, posterior, medial and lateral view. Scale bar is 25 mm. Chromatic scale corresponds to the look-up table of cortical thickness, from relatively thin (blue) to relatively thick (red) cortical diaphyseal bone. Posterior thickening of the cortical bone occurs at about the level of the nutrient foramen, where the ‘proto-linea aspera’ is the narrowest. The femoral cortical thickness distribution is also characterized by an anterior thinning, with a proximo-distal gradient. The lateral reinforcement pattern appears to parallel an insertion area including the mm. vastus lateralis and gluteus maximus proximally, and the attachment zone of the m. vastus intermedius distally. In medial view, the relative cortical thickening is restricted to the proximal portion of the femoral shaft, corresponding to the attachment of the m. vastus medialis. The third reinforcement occurs posteriorly at about 35-55% of the biomechanical length and corresponds to an insertion area delineated by the two mm. vasti and comprising the hip adductor and extensor (m. biceps femoris) muscles.

Extended Data Fig. 7 Comparative CSGP data for the Chadian femur and ulna.

a., b., c., Cross-sectional geometric properties at 80% of the femoral biomechanical length including percentage of cortical area (a, %CA.), second moments of area (b., Ix/Iy, and c., Imax/Imin). d., e., f., Cross-sectional geometric properties at 50% of the femoral biomechanical length including percent of cortical area (d, %CA,), second moments of area (e., Ix/Iy, and f., Imax/Imin). g., h., Second moments of area (g., Imax/Imin and h., Ix/Iy) at 50% of the ulna biomechanical length (TM 266-01-050). Extant apes are represented by mean (circle) and standard deviation (whiskers), whereas isolated circles represent individual values for fossil specimens. See Supplementary Table 2 specimen list. Ulnar data are from25,82. The yellowish frame encompasses the early hominin range of variation whereas the red dotted lines mark the mean values for Pan and extant Homo within each panel. For the femur: modern humans, n = 40; chimpanzees, n = 20; gorillas, n = 23; orangutans, n = 23; Miocene hominoids, n = 3; Miocene hominins, n = 3; australopiths, n = 5; early Homo, n = 6; neandertals, n = 9. For the ulna: modern humans, n = 19; chimpanzees, n = 17; gorillas, n = 14; orangutans, n = 14; gibbons, n = 16, Australopiths, n = 3.

Extended Data Fig. 8 Illustration of the calcar femorale of TM 266-01-063.

a, virtual representation of the proximal portion of the femur in posterior view, the asterisk marks the position of the parasagittal microCT-slice passing through the lesser trochanter; b, microCT-slice image of the parasagittal section showing the proximo-distal extension of the calcar femorale (cf) and b’, corresponding binarized image enhancing the calcar femorale; c, microCT-slice image of the parasagittal section in BAR 1003’00 femur (Or. tugenensis) showing the proximo-distal extension of the calcar femoral, and c’, corresponding binarized image; d, virtual representation of the proximal portion of the femur in posterior view showing transversal levels (i-vi) used for imaging the development of the calcar femorale (following29); e, microCT- slice images of the sections (i-vi as in TM 266-01-063) showing expression of the calcar femorale transversally (medial to the right and anterior to the top), and f, corresponding binarized version; g, microCT- slice images of the sections (i-vi) showing expression of the calcar femorale transversally in BAR 1003’00 (acquired from CT-scan data, this study). Scale bar for a, d, 10 mm; b, 6 mm; e, f, 4 mm.

Extended Data Fig. 9 Calcar femorale morphology in extant hominines.

The selected individuals corresponds to morphological extrema, i.e., the minimal and maximal degrees of expression of the calcar femorale, in our comparative sample (wild caught specimens). The boxes are for a, modern humans; b, chimpanzees (Pan paniscus); c, chimpanzees (Pan troglodytes); d, gorillas. For each box, parasagittal views are on the left (taken at the maximal possible degree of expression of the calcar femorale, around mid-width of the lesser trochanter, see lower right panel); transversal views are on the right (taken at the maximal possible degree of expression of the calcar femorale, ca at the proximal border of the lesser trochanter, see lower right panel). The asterisk marks an evidence of a calcar femorale. The calcar femorale is present in all modern humans of our sample; in parasagittal view, its expression displays a columnar aspect with an oblique orientation. The trabecular bundle forming the CF shows various degree of densification and thickness, from loose (e.g., third specimen from the top) to tightened (e.g., first and fourth specimens from the top). In transversal view, the CF forms a rather short spur originating from the thickened medial cortical bone. By contrast, most of our sampled non-human apes do not show any evidence of a columnar and oblique trabecular bundle. At best, a thin, curved, cancellous bone densification is identifiable in parasagittal view. In transversal view, the CF, when present, corresponds to a thin ray composed of few or single trabeculae, contrasting in this aspect with the modern human condition. Besides, the degree of development of the CF is associated with a relative thickening of the antero-medial cortical bone, but with a less extent in non-human apes than in modern humans. In modern humans, the thickening tends to be more medial than antero-medial. This configuration potentially enlightens the results from29 showing a lengthened CF in modern humans compared to non-human apes, as the absolute CF length was measured from the tip of the CF to the exterior cortical boundary.

Extended Data Fig. 10 Ulnar comparison of S. tchadensis and extinct and extant hominines.

a., lateral view; b., anterior view; c., medial view; d. posterior view. All ulnae are from 3D virtual models, except for A.L. 438-1 (modified from35), ALA-VP-2/101 (modified from33) and StW 573 (modified from10). Scale bar is 40 mm. F and M are for female and male.

Supplementary information

Supplementary Information

Includes Supplementary Notes 1–5 providing information on the context of discovery, fossil descriptions, comments on Figs. 2 and 3, comparisons of cortical thickness, cross-sectional geometric properties and definitions. In addition, Supplementary Tables 1 and 4 provide raw measurements and sample lists, respectively.

Reporting Summary

Supplementary Table 2

Comparative femoral cross-sectional geometric properties in extinct and extant apes.

Supplementary Table 3

Morphological state of the main preserved features in the femur and ulnae of S. tchadensis, and their comparative in the extant and extinct hominins.

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Daver, G., Guy, F., Mackaye, H.T. et al. Postcranial evidence of late Miocene hominin bipedalism in Chad. Nature 609, 94–100 (2022). https://doi.org/10.1038/s41586-022-04901-z

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