A partial pelvis of Australopithecus sediba

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21. D. Falk, Am. J. Phys. Anthropol. 53, 525 (1980). 22. P. Bailey, G. von Bonin, The Isocortex of the Chimpanzee (Univ. of Illinois Press, Urbana, IL, 1950). 23. A. E. Walker, J. F. Fulton, J. Anat. 71, 105, 9 (1936). 24. J. K. Rilling et al., Nat. Neurosci. 11, 426 (2008). 25. N. M. Schenker et al., Cereb. Cortex 20, 730 (2010). 26. K. Amunts et al., J. Comp. Neurol. 412, 319 (1999). 27. D. Falk, Science 221, 1072 (1983). 28. R. L. Holloway, Hum. Neurobiol. 2, 105 (1983). 29. B. Fischl et al., Cereb. Cortex 18, 1973 (2008). 30. D. C. Van Essen, Nature 385, 313 (1997). 31. D. Falk, in Progress in Brain Research, M. A. Hofman, D. Falk, Eds. (Elsevier, New York, 2011), vol. 195. 32. J. N. Darroch, J. E. Mosimann, Biometrika 72, 241 (1985). 33. K. Semendeferi, E. Armstrong, A. Schleicher, K. Zilles, G. W. Van Hoesen, Am. J. Phys. Anthropol. 106, 129 (1998). 34. J. K. Rilling, Evol. Anthropol. 15, 65 (2006). 35. K. Semendeferi, E. Armstrong, A. Schleicher, K. Zilles, G. W. Van Hoesen, Am. J. Phys. Anthropol. 114, 224 (2001). 36. M. L. Kringelbach, E. T. Rolls, Prog. Neurobiol. 72, 341 (2004). 37. S. Frey, M. Petrides, Proc. Natl. Acad. Sci. U.S.A. 97, 8723 (2000). 38. E. Koechlin, A. Hyafil, Science 318, 594 (2007). 39. D. Badre, M. D’Esposito, Nat. Rev. Neurosci. 10, 659 (2009). 40. D. Falk et al., Science 308, 242 (2005). 41. K. Semendeferi et al., Cereb. Cortex 21, 1485 (2011). Acknowledgments: We thank the South African Heritage Resource Agency for permits to work at the Malapa site;

the Nash family for granting access to the Malapa site and their continued support of research on the Malapa and John Nash Nature Reserves; the South African Department of Science and Technology, the South African National Research Foundation (particularly the African Origins Platform Initiative), the Institute for Human Evolution (IHE), the University of the Witwatersrand, the University of the Witwatersrand’s Vice Chancellor’s Discretionary Fund, the National Geographic Society, the Palaeontological Scientific Trust (PAST), the Andrew W. Mellon Foundation, the Ford Foundation, the United States Diplomatic Mission to South Africa, the French Embassy of South Africa, the Research Office of the University of the Witwatersrand, the Ray A. Rothrock ’77 Fellowship, the Program to Enhance Scholarly and Creative Activities, and International Research Travel Assistance Grant of Texas A&M University, the Oppenheimer and Ackerman families, and Sir Richard Branson for funding; the University of the Witwatersrand’s Schools of Geosciences and Anatomical Sciences and the Bernard Price Institute for Palaeontology for support and facilities; the Gauteng Government, Gauteng Department of Agriculture, Conservation and Environment, and the Cradle of Humankind Management Authority; and our respective institutions for ongoing support. For access to comparative specimens, we thank S. Potze, L. Kgasi, and the Ditsong National Museum of Natural History; B. Billings, D. Lieberman and the Peabody Museum of Archeology and Ethnology (Harvard University); E. Mbua, P. Kiura, V. Iminjili, and the National Museums of Kenya; and the University of Zurich 2009 and 2010 Field Schools. Numerous individuals assisted with ongoing preparation and excavation of the Malapa fossils, including C. Dube, S. Jilah, C. Kemp, M. Kgasi, M. Languza, J. Malaza,

A Partial Pelvis of Australopithecus sediba Job M. Kibii,1 Steven E. Churchill,2,1* Peter Schmid,3,1 Kristian J. Carlson,1,4 Nichelle D. Reed,2 Darryl J. de Ruiter,5,1 Lee R. Berger1,6 The fossil record of the hominin pelvis reflects important evolutionary changes in locomotion and parturition. The partial pelves of two individuals of Australopithecus sediba were reconstructed from previously reported finds and new material. These remains share some features with australopiths, such as large biacetabular diameter, small sacral and coxal joints, and long pubic rami. The specimens also share derived features with Homo, including more vertically oriented and sigmoid-shaped iliac blades, greater robusticity of the iliac body, sinusoidal anterior iliac borders, shortened ischia, and more superiorly oriented pubic rami. These derived features appear in a species with a small adult brain size, suggesting that the birthing of larger-brained babies was not driving the evolution of the pelvis at this time. he evolution of the hominin pelvis over the past four million years reflects functional accommodations to both terrestrial bipedalism and encephalization. The relative importance of these two factors in evolutionary

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1 Institute for Human Evolution, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. 2Department of Evolutionary Anthropology, Box 90383, Duke University, Durham, NC 27708 USA. 3Anthropological Institute and Museum, University of Zuerich, Winterthurerstr. 190, CH-8057 Zuerich, Switzerland. 4Department of Anthropology, Indiana University, Bloomington, IN 47405, USA. 5Department of Anthropology, Texas A&M University, College Station, TX 77843, USA. 6School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.

*To whom correspondence should be addressed. E-mail: [email protected]

change in the pelvis from Australopithecus to Homo, however, is unclear. One key fossil for assessing the evolutionary importance of differences between these genera is a pelvis (BSN 49/P27) from early Pleistocene [0.9 to 1.4 million years ago (Ma)] deposits at Gona, Ethiopia (1, 2). The taxonomic assignment of this pelvis is uncertain because it is not associated with craniofacial remains and it shares morphological features with both australopiths and Homo. Its great transverse breadth, laterally flaring ilia, anteriorly positioned iliac pillar, long pubic rami, and wide sciatic notches are australopith-like. It also shares derived features with Homo [table S6 in (1)], including a sigmoidshaped iliac crest, a tall posterior ilium, an expanded fossa for gluteus medius, and a narrow

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G. Mokoma, P. Mukanela, T. Nemvhundi, M. Ngcamphalala, S. Tshabalala, and C. Yates. Other individuals, contributing substantial support to this project include L. Backwell, D. Conforti, B. de Klerk, C. Dlamini, V. Fernandez, J. Kretzen, B. Kuhn, W. Lawrence, B. Louw, B. Nkosi, M. Peltier, L. Pollarolo, C. Steininger, F. Thackeray, H. Visser, and B. Zipfel. T.J. also would like to thank the Claude Leon Foundation for awarding her a postdoctoral fellowship. We acknowledge the ESRF ID17 beamline team, and the ESRF for granting beamtime under proposal ec521. We thank Charlotte Maxeke Johannesburg Academic Hospital and J. Smilg for facilitating computed tomography (CT) scans and Q. Letsoalo for assistance in conducting them; D. Falk, R. Holloway, and R. Clarke for discussions on hominin fossils in South Africa; T. Preuss and J. Rilling for images and discussions of chimpanzee cortical anatomy; M. Dowdeswell for statistical guidance; S. Hurst for permitting use of CT data from Sts 60 and Sterkfontein Type 2 endocasts; and the editor and three anonymous reviewers for their comments. Image data of the MH1 cranium and endocast are curated in the IHE at the University of the Witwatersrand and at ESRF.

Supporting Online Material www.sciencemag.org/cgi/content/full/333/6048/1402/DC1 Materials and Methods SOM Text Figs. S1 to S10 Table S1 References (42, 43) 7 February 2011; accepted 29 July 2011 10.1126/science.1203922

tuberoacetabular sulcus. The Homo-like features in this pelvis have been argued to be architectural responses to the obstetric demands of birthing larger-brained babies (1). Without a clear taxonomic association, however, scenarios of pelvic evolution and encephalization based on the Gona pelvis remain conjectural [see (2)]. The pelves of early Pleistocene Homo (KNMER 3228, KNM-ER 5881, OH 28, and KNM-WT 15000) share with modern humans a suite of features that include a thick iliac body, reduced (relative to body size) distance from the auricular to acetabular joint surfaces, expansion of the retroauricular area, a large iliac tuberosity, vertically set iliac blades, a sigmoid-shaped iliac crest with moderate- to well-developed fossae for iliacus and gluteus medius, a distinct iliac pillar, a sinusoidal anterior iliac border, and a narrow tuberoacetabular sulcus (1, 3–7). Many of these features are seen in the pelvic remains of two fairly complete individuals of Australopithecus sediba from Malapa (8). Here, we describe newly found and previously unpublished fossils of the adult female paratype (Malapa Hominin 2, MH2) that allow us to reconstruct her pelvis. We also reconstruct, from previously published fragments (8), the pelvis of the juvenile male holotype (MH1). Given the clear association of these pelvic remains with a small-brained species that was close to the transition of Australopithecus to Homo, these fossils provide information about the role of brain size expansion in the evolution of Homo-like pelvic architecture. The remains attributed to the juvenile male MH1 include partial right and left ilia and a left ischium [supporting online material (SOM) text

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S1]. The right (complete) and left (fragmentary) pubic bones of the adult female MH2 have been previously described (8). We have now recovered part of her right ilium and sacrum (Fig. 1). The ilium preserves most of the blade and the superior half of the acetabulum. There is a moderate sigmoid curvature to the iliac crest, with a relatively deep gluteus medius fossa and a shallow yet distinct iliacus fossa. Although the anterior superior iliac spine (ASIS) is missing, the preserved anterior portion of the blade curves medially, denoting a medially displaced ASIS as in Homo. The inferior portion of the iliac pillar is present as an indistinct thickening. MH2 shares with other australopiths relatively small sacroiliac and coxal joint surfaces and an auricular surface that is small relative to acetabular diameter (SOM text S2.1). On the basis of the remains of both individuals, the os coxa of Au. sediba is also plesiomorphic (that is, similar to temporally earlier species of Australopithecus) in a number of details (Table 1), including having a long pubic ramus with a medially positioned pubic tubercle and a marked angle between the facet of the adductor magnus and that of the semitendinosus and semimembranosus on the ischial tuberosity. In addition, on the basis of morphology of the pubic symphyseal face of MH2, Au. sediba may not have possessed the apomorphic feature of delayed fusion of the pubic apophysis, which is a developmental feature that contributes to sexual dimorphism in modern humans (9). This, along with the fairly wide sciatic notch of MH1 (8) and low subpubic angle of MH2 (Table 2), suggests that Au. sediba may not have expressed the marked sexual dimorphism that characterizes the pelves of modern humans. The sacrum of MH2 is incomplete: Almost the entirety of its left ala and most of the auricular surface of its right ala are missing. The sacrum is curved in sagittal profile and is anteroposteriorly thicker than the sacra of AL 288-1 (Au. afarensis) and Sts 14 (Au. africanus), but is not as thick as that of Stw 431 (Au. africanus). As in modern humans and Stw 431 (but not AL 288-1 or Sts 14), the auricular surface extends onto the third sacral vertebra. The MH2 sacrum is plesiomorphic in having mediolaterally broad alae with nonrugose attachments for the inferior portion of the posterior sacroiliac ligament. In most other characters, the ossa coxae and sacrum of Au. sediba exhibit derived morphology either characteristic of Pleistocene and/or modern Homo or intermediate between Australopithecus and Homo (Table 1). The meaning of the derived features in the Au. sediba pelvis is unclear, because debate exists as to the functional implications of these features in Homo. In one model, australopiths were habitual terrestrial bipeds but retained a substantial arboreal component to their locomotor repertoire (10–12). Accordingly, the competing selective demands of arboreal climbing and terrestrial bipedalism constrained the extent to which selection could favor adaptations in the pelvis for more effective bipedalism. Because of stabilizing selection for morphological competence in climbing,

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australopith bipedalism involved kinematics like those used by apes in vertical climbing, with more flexed positions of the hip and knee during single-leg support than is seen in the striding bipedalism of living humans (13, 14). According to this kinematic-shift model, the changes in the pelvis of early Homo reflect the relaxation of this constraint (i.e., a full commitment to terrestrial locomotion) and the emergence of a more effective and efficient form of full-striding bipedalism (15, 16). An alternative model is that the morphological contrasts between australopiths and Homo represent obstetric rather than locomotor differences between them (9, 17). If so, the kinematics of bipedalism may have differed little between Australopithecus and Homo, but brain size expansion in the latter favored larger birth canals and necessitated changes in overall pelvic architecture. Birthing of bigger-brained babies would have been facilitated by three interrelated architectural changes: an increase in the sagittal relative to the transverse diameter of the pelvic inlet and outlet, an increase in the absolute transverse diameter of the inlet and outlet, and an elevation of the anterior portion of the midplane brought about by an upward rotation of the pubic corpora and a downward rotation of the ischial corpora (9). These structural changes secondarily produced a relative reduction in the length of the superior pubic rami (9), more vertical and less laterally flared ilia (9), more robust and posteriorly positioned iliac pillars (17), greater robusticity of the ilia (17), and a narrowing of the tuberoacetabular sulcus (9).

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Because in this model both primary and secondary changes are thought to reflect obstetric accommodations to larger-brained babies, we would expect the small-brained species Au. sediba to exhibit the primitive condition for all of these traits. The estimated adult endocranial volume (ECV) of MH1, at ~420 to 440 cm3 (8), is below but within one standard deviation of the mean ECVof Au. afarensis and Au. africanus (18). Thus, brain size in Au. sediba neonates was likely no greater than that of other gracile australopiths [between ~153 to 201 cm3 (18, 19)], and adult female body size does not appear to differ between these species (8). Accordingly, there is no reason to suspect that fetal cephalic-maternal pelvic disproportion was a selective factor in the establishment of Au. sediba pelvic morphology. Consideration of the obstetrically important diameters of the reconstructed MH2 pelvis supports this interpretation. Both the sacrum and the right pubis of MH2 retain points of contact with the ilium, which allows us to reconstruct with great confidence the pelvis of this individual (Fig. 2), albeit without the ischium. Sufficient portions of the MH1 pelvis are present so as to permit reconstruction of that specimen as well (Fig. 2), although with less confidence. (For details of the reconstruction of both pelves, see SOM text S1.) The diameters of the pelvic inlet of the adult female MH2 do not differ substantially from those of A.L. 288-1 (Au. afarensis) and Sts 14 (Au. africanus) (Table 2). The pelvic inlet of MH2 is more gynaecoid (i.e., having a relatively greater sagittal dimension) than the markedly platypelloid (transversely Fig. 1. (Top) Coxal remains of MH2 in internal (left) and external (right) perspectives. (Bottom) MH2 sacrum in ventral (left), lateral (center), and dorsal (right) views. Portions of the pedicles and laminae of the ultimate and penultimate lumbar vertebrae are cemented by matrix to the superior portion of the bone (removed by virtual preparation, fig. S4). Scale bars in centimeters.

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broad) pelvis of AL 288-1 (Au. afarensis) but is similar to the Au. africanus specimen Sts 14 (Table 2). As with the Gona pelvis (1), relative sagittal expansion of the inlet appears to have been accomplished both by a greater anterior projection of the pubic rami and superiorward reorientation of the pubic corpora. Although the birth canal of MH2 is more gynaecoid than that of AL 288-1, it is less so than that of Gona or living humans. This difference (along with expansion of the transverse diameter) likely reflects later obstetric accommodations to encephalization

in the latter. Still, two of the architectural features thought to characterize the Homo pelvis—increased relative sagittal diameter of the birth canal and upward rotation of the pubis—had emerged in this late australopith (20). As with other small-brained australopiths, the pubic ramus of MH2 is relatively long, and the iliac pillar is weakly developed and anteriorly positioned. Pubic length relative to acetabular diameter in MH2 (2.01) is somewhat greater than even that of AL 288-1 (1.95) and Sts 14 (1.73) [using minimum pubic lengths for the latter two

Table 1. Morphological features of the Au. sediba pelvis. The adjective “relative” and the adverb “relatively” should be taken to mean “relative to body size.” Adjectives such as “reduced,” “increased,” “expanded,” etc. are relative to the condition normally found in the two best known species of Australopithecus, Au. afarensis and Au. africanus. Reference Plesiomorphic features shared with other australopiths Large relative biacetabular diameter Anteriorly positioned and indistinct iliac pillar* Relatively small sacral and acetabular joint surfaces Marked angle between facets for hamstring muscles and adductor magnus Weakly developed iliopubic eminence Relatively long pubis Medially positioned pubic tubercle Early (compared to modern humans) fusion of the secondary centers of ossification of the pubic symphysis† Mediolaterally broad sacral alae (relative to centrum size) Small dorsal sacral intermediate fossa (for sacroiliac ligaments) Nonrugose and nonprominent inferior margin of lateral sacral ridge Moderate or no sexual dimorphism in pelvic shape

(27) (34) (27) (12) (12) (27) (1) (9) (1, 35) (1) (1) (1)

Features intermediate between australopiths and Homo Greater sagittal (more vertical) orientation of iliac blades Sigmoid curvature of the iliac crest (with strongly developed fossae for the iliacus and gluteus medius) and medial reflection of the ASIS Increased buttressing of the iliac body (enlargement of the acetabulosacral buttresses) Pronounced and more rugose iliofemoral ligament attachment area‡ Features shared synapomorphically or homoplastically with Homo Reduced relative distance from the sacroiliac to hip joints Expansion of the posterior portion of the ilium (notably the retroauricular area) Pronounced iliac tuberosity Sinusoidal anterior iliac border Shelf-like attachment of the reflected head of rectus femoris Shortened ischium (including a relatively narrow tuberoacetabular sulcus) Everted ischial tuberosity§ More superior position of superior pubic ramus Superoinferior elongation of the pubic symphyseal face||; less ovoid, more rectangular symphysis Increased curvature of the sacrum in the sagittal plane Enlarged transverse processes (dorsal alar tubercle or “upper lateral angles”) on the first sacral vertebrae¶ Auricular surface of sacrum extends to S3 Increased lumbosacral angle Relative enlargement of the anteroposterior dimension of the pelvic inlet (resulting in a less platypelloid and more gynaecoid inlet shape)#

(12, 17) (3, 12) (3, 4) (3, 12)

(3) (3) (36) (1, 4) (1) (12, 35) (3) (9, 37) (1, 12, 38) (12) (12)

(39) (9, 40)

*Morphology varies between MH1 and MH2; see main text and SOM text S2.2 for discussion. †MH2 exhibits a fully fused symphyseal secondary center of ossification, but given her adult status and unknown age at death, it cannot be determined with certainty that Au. sediba possessed the primitive state for this feature. ‡Variably expressed in Au. sediba; MH1 is rugose; MH2, nonrugose. §Characteristic of early Homo but not of modern humans. ||Actually superoanterior to inferoposterior in anatomical position. ¶See SOM text S1. #Also seen in the Au. africanus pelves Sts 14 (41) and Stw 431 (23).

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specimens from (21)] and substantially longer than that of modern human females [1.48, based on mean values in (22)]. As for the iliac pillar, Au. sediba appears to be variable; MH2 exhibits the usual australopith pattern of an indistinct thickening of the anterolateral portion of the iliac blade, whereas MH1 possesses a distinct (Homo-like) buttress. However, when the thickness of this buttress is evaluated metrically, Au. sediba is indistinguishable from other australopiths (SOM text S2.2). Additionally, the buttress in MH1 was initially described (8) as being more posteriorly positioned, as in Homo. However, subsequent attempts to quantify buttress position suggest that this observation was in error and that it may instead have been anteriorly positioned in MH1 (SOM text S2.2). Although pubic length and anterior iliac buttressing conform to the predictions of the obstetric model, other features of the Au. sediba pelvis do not. Most notably, the iliac blades are decidedly Homo-like in their vertical orientation, well-defined sigmoid curvature, and medial displacement of the ASIS (SOM text S2.3). Although it is also the case that MH2 has reduced lateral flare of the iliac blades [commonly thought to be a derived feature of later Homo (1)], this feature does not differ significantly between any of the groups (SOM text S2.3). This change in shape and orientation of the iliac blade is presaged by a change in iliac orientation in Au. africanus relative to Au. afarensis (23) and by the enhanced sigmoid curvature seen in the juvenile Au. africanus specimen MLD 25 from Makapansgat and a taxonomically uncertain [but most likely Au. robustus (24)] specimen from Swartkrans, SK 3155b. These specimens, together with MH2, indicate that morphological changes in the direction of Homo are apparent in some individuals belonging to smallbrained species. It has been suggested that vertical reorientation and reduced lateral flare of the iliac blades in Homo reduced the mechanical advantage of the gluteal muscles, resulting in higher joint reaction forces in the hip and greater bending moments on the femoral neck in the supporting limb during the stance phase in walking (9, 17). This reduction in gluteal leverage and the attendant increases in stress in the proximal femur may have provided the selective context that favored a reduction in the relative length of the femoral neck and an increase in relative femoral head size in the genus Homo (9, 17). Relative biomechanical neck length (standardized by femoral head diameter) in MH1 (1.8), however, is within one standard deviation of the mean value for other australopiths (1.9 T 0.14, n = 4), despite the vertically set iliac blade in Au. sediba. This might suggest that shortening of the neck was not necessary until body mass increased in the Homo lineage. As in Homo, the weight transfer region of the iliac body of the Malapa hominins is more robust than that of other australopiths, manifested by greater thickness of the acetabulosacral buttress

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and shortening of the acetabulosacral load arm. The mean value of the ratio of these measures for Au. sediba lies 6.5 standard deviations above that of other australopiths (SOM text S2.4). Structural reinforcement of the load-bearing regions of the ilium (25) might indicate increased force transduction through the pelvis relative to earlier australopiths, although the small sacroiliac and hip joints appear to contravene this idea. However, Au. sediba has a relatively large postauricular portion of the iliac blade (SOM text S2.5) along with hypertrophy of the interosseous and short posterior sacroiliac ligaments (as evidenced by expansion of the area of the iliac tuberosity and by an apparent hypertrophy of the sacral dorsal alar tubercle; see SOM text S1), perhaps implying higher magnitude nutational moments at the sacroliliac joint.

Lastly, on the basis of the morphology of MH1, Au. sediba shares with Homo a superoinferiorly short ischium, resulting in a narrow tuberoacetabular sulcus and a relatively reduced lever arm for the hamstring muscles (SOM text S2.6). The moment arm of the hamstrings, when scaled to minimum iliac breadth (as a control for body size), falls 5.4 standard deviations below the mean value for other australopiths. It is not clear whether this reflects selection related to a change in the role of these muscles in locomotion (12) or a pleiotropic consequence of further superoinferior shortening of the iliac body beyond that already attained by earlier australopiths (as reflected in a reduced acetabulosacral distance; see above). Thus, Au. sediba is australopith-like in having a long superior pubic ramus and an anteriorly

Table 2. Obstetric dimensions and indices of female fossil and extant hominid pelves. All measurements as defined by (42). All measurements on MH2 were taken on a virtual reconstruction of the pelvis (SOM text S1). AL 288-1 dimensions are from (40) unless otherwise noted, Sts 14 dimensions are from (41), and BSN 49/P27 dimensions are from the supporting online material of (1). Homo sapiens weighted averages were calculated from means and sample sizes of six female samples from (42); SD indicates standard deviation of the weighted mean; pooled sample sizes ranged from 191 to 311. Pan troglodytes combined sex sample, data from (41): n = 29; 6 males, 5 females, 18 unknown sex. BIB, bi-iliac breadth (false pelvis transverse diameter); BAD, biacetabular diameter; SD, sagittal diameter (anteroposterior diameter); TD, transverse diameter; dash entries, no data available. Parentheses denote estimated values. MH2 BIB (250) BAD 122.3 BIB/BAD 2.04 Inlet SD 81.7 Inlet TD 117.6 Inlet SD/TD index 69.5 Midplane SD 97.9 Outlet SD 97.4 Subpubic angle 76.0°

AL 288-1

Sts 14

BSN 49/P27

268.3* 118.0* 2.27 76.0 132.0 57.6 – 71.0 81.0°

256.3 107.5 2.38 83.0 116.8 71.1 – – 107.2°

288.0 131.0 2.20 98.0 124.5 78.7 – – 110.0°

H. sapiens

P. troglodytes

Mean

SD

Mean

SD

259.5 123.2 2.10 105.2 131.6 80.0 125.1 119.4 89.6°

16.4 6.5 0.13 19.1 10.4 17.4 16.0 17.8 12.3°

122.4 105.8 1.16 143.7 100.0 146.1 137.5 122.4 –

18.3 35.6 12.6 12.3 20.1 26.8 9.6 –

*Dimensions from Schmid’s reconstruction (43), as reported by (41).

Fig. 2. Comparison of the MH1 (left), Sts 14 (center), and MH2 (right, mirror-imaged) pelves in anteroinferior (top row) and anterosuperior (bottom row) views. Areas represented in white or light gray in the MH1 and MH2 pelves represent reconstructed portions of the pelvis (SOM text S1). Sts 14 is attributed to Au. africanus and is represented by the virtual reconstruction of (41). Scale bar in centimeters [note that the anterosuperior view of Sts 14, as provided by (41), is in a slightly different orientation than those of MH1 and MH2]. An additional comparison is provided in fig. S7.

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positioned and indistinctly developed iliac pillar, which is consistent with the obstetric model. However, Au. sediba is Homo-like in having vertically oriented and sigmoid-shaped iliac blades, more robust ilia, and a narrow tuberoacetabular sulcus (26), contra the obstetric model. Pelvic inlet shape is more gynacoid than that of AL 288-1 (as is that of Sts 14) but less so than that of the Gona pelvis or modern humans (Table 2), and the pubic body is upwardly rotated as in Homo. Taken together, these features show that architectural reorganization of the pelvis and the emergence of derived Homo-like characters preceded, in at least one lineage of early hominins, substantial brain size expansion. The derived features in the pelvis of Au. sediba are not allometric consequences of increased body size (27). Femoral head diameters and other indicators of body size in Au. sediba fall at the low end of, but completely within, the range of values known for Au. afarensis and Au. africanus (8): Major increases in hominin body size appear to begin only with H. erectus (2). Similarly, Homo-like features in the pelvis of the smallbodied individual from Gona cannot be attributed to body size allometry (1). The Gona pelvis possesses a mix of primitive and derived features different than that seen in Au. sediba, involving a larger and more gynaecoid birth canal and less vertical and somewhat less sigmoid-shaped iliac blades. Although different than MH2, the morphology of the Gona pelvis also argues against the obstetric model, in that it has long pubic rami and australopith-like iliac blades despite an enlarged and gynaecoid birth canal. We propose that the derived features of Au. sediba reflect a close phyletic relationship with Homo, although it is possible that these features are homoplasies (28). Regardless, even if Au. sediba is not ancestral to Homo, it demonstrates that derived Homo-like features in the pelvis can occur independently of encephalization and the birthing of large-brained neonates. The functional importance of the reorganization of biomechanically important aspects of the pelvis of Au. sediba, in the absence of increased encephalization or body size, is not entirely clear. The basic postcranial anatomy of early australopiths, characterized by the retention of numerous features that have been interpreted as adaptations for climbing, persisted relatively unchanged for nearly two million years. This long-term stasis appears to reflect a stable locomotor adaptation in the absence of directional selection for improved terrestrial competence (29). Although evidence against the obstetric model is not ipso facto evidence for the kinematic-shift model, the appearance of derived features of the pelvis in Au. sediba, after such a long period of stasis and in the absence of altered obstetric demands, seems most parsimoniously attributed to altered biomechanical demands on the pelvis in locomotion. This in turn may be related to a change in the nature of exploitation of terrestrial environments [but within the context of continued reliance on

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arboreal habitats, see (30, 31)], perhaps associated with an expansion of grassland ecosystems in the South African Plio-Pleistocene (32, 33). Although there is no doubt that the eventual expansion of brain size in the genus Homo had a substantial impact on the functional morphology of the pelvis (and on the establishment of human pelvic sexual dimorphism), evidence from Au. sediba suggests that locomotor rather than obstetric demands drove the emergence of the basic Homo pelvic bauplan. References and Notes 1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

21. 22. 23.

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24. H. M. McHenry, R. S. Corruccini, Am. J. Phys. Anthropol. 43, 263 (1975). 25. M. Dalstra, R. Huiskes, J. Biomech. 28, 715 (1995). 26. All of these features can be observed and quantified in the unreconstructed fossils. Our assessment of pelvic inlet shape and the orientation of the pubic corpora are dependent on our reconstruction, but these determinations are certain to be reasonable given the nature of the contacting surfaces and the constraints that guided the reconstruction (SOM text S1). 27. C. Berge, J.-B. Kazmierczak, Folia Primatol. 46, 185 (1986). 28. B. Wood, T. Harrison, Nature 470, 347 (2011). 29. C. V. Ward, Yearb. Phys. Anthropol. 119 (suppl. 35), 185 (2002). 30. T. L. Kivell, J. M. Kibii, S. E. Churchill, P. Schmid, L. R. Berger, Science 333, 1411 (2011). 31. B. Zipfel et al., Science 333, 1417 (2011). 32. M. Sponheimer, J. A. Lee-Thorp, “Biogeochemical evidence for the environments of early Homo in South Africa,” in The First Humans: Origin and Early Evolution of the Genus Homo., F. E. Grine, J. G. Fleagle, R. E. Leakey, Eds. (Springer, Dordrecht, Netherlands, 2009), pp. 185–194. 33. A. I. R. Herries, P. J. Hopley, J. W. Adams, D. Curnoe, M. A. Maslin, Am. J. Phys. Anthropol. 143, 640 (2010). 34. J. L. de Arsuaga, J. Hum. Evol. 10, 293 (1981). 35. Y. Haile-Selassie et al., Proc. Natl. Acad. Sci. U.S.A. 107, 12121 (2010). 36. L. C. Aiello, M. C. Dean, An Introduction to Human Evolutionary Anatomy (Academic Press, London, 1990). 37. C. Berge, R. Orban-Segebarth, P. Schmid, J. Hum. Evol. 13, 573 (1984). 38. L. Bondioli et al., J. Hum. Evol. 50, 479 (2006). 39. M. M. Abitbol, Am. J. Phys. Anthropol. 72, 361 (1987). 40. R. G. Tague, C. O. Lovejoy, J. Hum. Evol. 15, 237 (1986). 41. C. Berge, D. Goularas, J. Hum. Evol. 58, 262 (2010). 42. R. G. Tague, Am. J. Phys. Anthropol. 80, 59 (1989). 43. P. Schmid, Folia Primatol. 40, 283 (1983). Acknowledgments: We thank the South African Heritage Resource Agency for the permits to work at the Malapa site; the Nash family for granting access to the Malapa site and continued support of research on their reserve; the South African Department of Science and Technology, the South African National Research Foundation, the Institute for Human Evolution, University of the Witwatersrand, the University of the Witwatersrand’s Vice Chancellor’s Discretionary Fund, the National

Australopithecus sediba Hand Demonstrates Mosaic Evolution of Locomotor and Manipulative Abilities Tracy L. Kivell,1 Job M. Kibii,2* Steven E. Churchill,3,2 Peter Schmid,4,2 Lee R. Berger2,5 Hand bones from a single individual with a clear taxonomic affiliation are scarce in the hominin fossil record, which has hampered understanding the evolution of manipulative abilities in hominins. Here we describe and analyze a nearly complete wrist and hand of an adult female [Malapa Hominin 2 (MH2)] Australopithecus sediba from Malapa, South Africa (1.977 million years ago). The hand presents a suite of Australopithecus-like features, such as a strong flexor apparatus associated with arboreal locomotion, and Homo-like features, such as a long thumb and short fingers associated with precision gripping and possibly stone tool production. Comparisons to other fossil hominins suggest that there were at least two distinct hand morphotypes around the Plio-Pleistocene transition. The MH2 fossils suggest that Au. sediba may represent a basal condition associated with early stone tool use and production.

T

he extraordinary manipulative skills of the human hand are viewed as a hallmark of humanity (1). Over the course of hu-

man evolution, the hand was freed from the constraints of locomotion and has evolved primarily for manipulation, including tool use and even-

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Geographic Society, the Palaeontological Scientific Trust, the Andrew W. Mellon Foundation, the Ford Foundation, the U.S. Diplomatic Mission to South Africa, the French Embassy of South Africa, the A. H. Schultz Foundation, a Ray A. Rothrock ’77 fellowship and an International Research Travel Assistance grant of Texas A&M University, the Oppenheimer and Ackerman families, and R. Branson for funding; the University of the Witwatersrand’s Schools of Geosciences and Anatomical Sciences and the Bernard Price Institute for Palaeontology for support and facilities; the Gauteng Government, Gauteng Department of Agriculture, Conservation and Environment and the Cradle of Humankind Management Authority; and our respective universities for ongoing support. For access to comparative specimens, we thank E. Mbua, P. Kiura, V. Iminjili, and the National Museums of Kenya; B. Billings, B. Zipfel, and the School of Anatomical Sciences at the University of the Witwatersrand; and S. Potze, L.C. Kgasi, and the Ditsong Museum. For comparative data, we thank T. Holliday. For technical and material support, we thank Duke University and the University of Zurich 2009 and 2010 Field Schools. Numerous individuals have been involved in the ongoing preparation and excavation of these fossils, including C. Dube, C. Kemp, M. Kgasi, M. Languza, J. Malaza, G. Mokoma, P. Mukanela, T. Nemvhundi, M. Ngcamphalala, S. Jirah, S. Tshabalala, and C. Yates. Other individuals who have given significant support to this project include B. de Klerk, W. Lawrence, C. Steininger, B. Kuhn, L. Pollarolo, B. Zipfel, J. Kretzen, D. Conforti, J. McCaffery, C. Dlamini, H. Visser, R. McCrae-Samuel, B. Nkosi, B. Louw, L. Backwell, F. Thackeray, and M. Peltier. J. Smilg facilitated computed tomography scanning of the specimens. J. DeSilva, T. Kivell, and three anonymous reviewers gave useful comments on drafts of the manuscript. The Au. sediba specimens are archived at the Institute of Human Evolution at the University of the Witwatersrand.

Supporting Online Material www.sciencemag.org/cgi/content/full/333/6048/1407/DC1 SOM Text S1 and S2 Figs. S1 to S17 Tables S1 to S7 References (44–52) 5 January 2011; accepted 29 July 2011 10.1126/science.1202521

tually tool production (2–5). Understanding this functional evolution has been hindered by the rarity of relatively complete hand skeletons that can be reliably assigned to a given taxon, based on a clear association with craniodental fossils. Only one fossil—the Olduvai Hominid 7 (OH 7) hand attributed to Homo habilis (6, 7)—had met these criteria during the interval between the first appearance of stone tools at 2.6 million years ago (Ma) (8) and the appearance of derived, essentially human-like morphology by 0.8 Ma (9). Here we describe an almost complete hand of Australopithecus sediba at 1.977 Ma (10) from

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REPORTS

1 Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig 04103, Germany. 2Institute for Human Evolution, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa. 3Department of Evolutionary Anthropology, Duke University, Box 90383, Durham, NC 27708, USA. 4Anthropological Institute and Museum, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland. 5School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.

*To whom correspondence should be addressed. E-mail: [email protected]

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