A new absolute date from Swartkrans Cave for the oldest occurrences of Paranthropus robustus and Oldowan stone tools in South Africa.

The Early Pleistocene site of Swartkrans in South Africa's Cradle of Humankind World Heritage Site has been significant for our understanding of the evolution of both early Homo and Paranthropus, as well as the earliest archaeology of southern Africa. Previous attempts to improve a faunal age estimate of the earliest deposit, Member 1, had produced results obtained with uranium-lead dating (U-Pb) on flowstones and cosmogenic burial dating of quartz, which placed the entire member in the range of >1.7/1.8 Ma and <2.3 Ma. In 2014, two simple burial dates for the Lower Bank, the earliest unit within Member 1, narrowed its age to between ca. 1.8 Ma and 2.2 Ma. A new dating program using the isochron method for burial dating has established an absolute age of 2.22 ± 0.09 Ma for a large portion of the Lower Bank, which can now be identified as containing the earliest Oldowan stone tools and fossils of Paranthropus robustus in South Africa. This date agrees within one sigma with the U-Pb age of 2.25 ± 0.08 Ma previously published for the flowstone underlying the Lower Bank and confirms a relatively rapid rate of accumulation for a large portion of the talus.

The pectoral girdle of StW 573 ('Little Foot') and its implications for shoulder evolution in the Hominina.

The ca. 3.67 Ma adult skeleton known as 'Little Foot' (StW 573), recovered from Sterkfontein Member 2 breccia in the Silberberg Grotto, is remarkable for its morphology and completeness. Preservation of clavicles and scapulae, including essentially complete right-side elements, offers opportunities to assess morphological and functional aspects of a nearly complete Australopithecus pectoral girdle. Here we describe the StW 573 pectoral girdle and offer quantitative comparisons to those of extant hominoids and selected homininans. The StW 573 pectoral girdle combines features intermediate between those of humans and other apes: a long and curved clavicle, suggesting a relatively dorsally positioned scapula; an enlarged and uniquely proportioned supraspinous fossa; a relatively cranially oriented glenoid fossa; and ape-like reinforcement of the axillary margin by a stout ventral bar. StW 573 scapulae are as follows: smaller than those of some homininans (i.e., KSD-VP-1/1 and KNM-ER 47000A), larger than others (i.e., A.L. 288-1, Sts 7, and MH2), and most similar in size to another australopith from Sterkfontein, StW 431. Moreover, StW 573 and StW 431 exhibit similar structural features along their axillary margins and inferior angles. As the StW 573 pectoral girdle (e.g., scapular configuration) has a greater affinity to that of apes-Gorilla in particular-rather than modern humans, we suggest that the StW 573 morphological pattern appears to reflect adaptations to arboreal behaviors, especially those with the hand positioned above the head, more than human-like manipulatory capabilities. When compared with less complete pectoral girdles from middle/late Miocene apes and that of the penecontemporaneous KSD-VP-1/1 (Australopithecus afarensis), and mindful of consensus views on the adaptiveness of arboreal positional behaviors soliciting abducted glenohumeral joints in early Pliocene taxa, we propose that the StW 573 pectoral girdle is a reasonable model for hypothesizing pectoral girdle configuration of the crown hominin last common ancestor.

Trabecular organization of the proximal femur in Paranthropus robustus: Implications for the assessment of its hip joint loading conditions.

Reconstruction of the locomotor repertoire of the australopiths (Australopithecus and Paranthropus) has progressively integrated information from the mechanosensitive internal structure of the appendicular skeleton. Recent investigations showed that the arrangement of the trabecular network at the femoral head center is biomechanically compatible with the pattern of cortical bone distribution across the neck, both suggesting a full commitment to bipedalism in australopiths, but associated with a slightly altered gait kinematics compared to Homo involving more lateral deviation of the body center of mass over the stance limb. To provide a global picture in Paranthropus robustus of the trabecular architecture of the proximal femur across the head, neck and greater trochanter compartments, we applied techniques of virtual imaging to the variably preserved Early Pleistocene specimens SK 82, SK 97, SK 3121, SKW 19 and SWT1/LB-2 from the cave site of Swartkrans, South Africa. We also assessed the coherence between the structural signals from the center of the head and those from the trabecular network of the inferolateral portion of the head and the inferior margin of the neck, sampling the so-called vertical bundle, which in humans represents the principal compressive system of the joint. Our analyses show a functionally related trabecular organization in Pa. robustus that closely resembles the extant human condition, but which also includes some specificities in local textural arrangement. The network of the inferolateral portion of the head shows a humanlike degree of anisotropy and a bone volume fraction intermediate between the extant human and the African ape patterns. These results suggest slight differences in gait kinematics between Pa. robustus and extant humans. The neck portion of the vertical bundle revealed a less biomechanically sensitive signal. Future investigations on the australopith hip joint loading environment should more carefully investigate the trabecular structure of the trochanteric region and possible structural covariation between cortical bone distribution across the neck and site-specific trabecular properties of the arcuate bundle.

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism.

Functional morphology of the atlas reflects multiple aspects of an organism's biology. More specifically, its shape indicates patterns of head mobility, while the size of its vascular foramina reflects blood flow to the brain. Anatomy and function of the early hominin atlas, and thus, its evolutionary history, are poorly documented because of a paucity of fossilized material. Meticulous excavation, cleaning and high-resolution micro-CT scanning of the StW 573 ('Little Foot') skull has revealed the most complete early hominin atlas yet found, having been cemented by breccia in its displaced and flipped over position on the cranial base anterolateral to the foramen magnum. Description and landmark-free morphometric analyses of the StW 573 atlas, along with other less complete hominin atlases from Sterkfontein (StW 679) and Hadar (AL 333-83), confirm the presence of an arboreal component in the positional repertoire of Australopithecus. Finally, assessment of the cross-sectional areas of the transverse foramina of the atlas and the left carotid canal in StW 573 further suggests there may have been lower metabolic costs for cerebral tissues in this hominin than have been attributed to extant humans and may support the idea that blood perfusion of these tissues increased over the course of hominin evolution.

Cortical bone distribution in the femoral neck of Paranthropus robustus.

Studies of the australopith (Australopithecus and Paranthropus) proximal femur have increasingly integrated information from the local arrangement of the cortical and cancellous bone to allow functional-biomechanical inferences on the locomotor behavioral patterns. In Australopithecus africanus and Paranthropus robustus, the cancellous bone organization at the center of the femoral head shows principal strut orientation similar to that of fossil and recent humans, which indicates that australopiths were human-like in many aspects of their bipedalism. However, by combining outer morphology with superoinferior asymmetry in cortical bone thickness at the base of neck and mid-neck, it has been suggested that, while adapted for terrestrial bipedality, australopiths displayed a slightly altered gait kinematics compared to Homo. We used techniques of 2D and 3D virtual imaging applied to an X-ray microtomographic record to assess cortical bone distribution along the entire femoral neck compartment in four upper femora from Swartkrans, South Africa (SK 82, SK 97, SK 3121, and SWT1/LB-2) and compared the results to the extant human and chimpanzee conditions. Our results support and extend previous evidence for more symmetric superior and inferior femoral neck cortical thicknesses in P. robustus than in modern humans and show that the differences are even greater than previously reported. However, P. robustus and humans still share a trend of lateral-to-medial decrease in asymmetry of the superior/inferior cortical thickness ratio, while this pattern is reversed in chimpanzees. We also identified two features uniquely characterizing P. robustus: an accentuated contrast between the relatively thicker anterior and the thinner posterior walls, and a more marked lateral-to-medial thinning of both cortices compared to extant humans and chimpanzees, which indicate wider interspecific differences among hominids in structural organization of the proximal femur than previously reported. It remains to be ascertained if, and to what extent, these features also characterize the femoral neck of Australopithecus.

The long limb bones of the StW 573 Australopithecus skeleton from Sterkfontein Member 2: Descriptions and proportions.

Due to its completeness, the A.L. 288-1 ('Lucy') skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like chimp/human last common ancestor (CLCA); (2) indication of some degree of climbing ability; (3) allometry. Recent discoveries of other partial skeletons of Australopithecus, such as those of Australopithecus sediba (MH1 and MH2) and Australopithecus afarensis (KSD-VP-1/1 and DIK-1/1), have provided new opportunities to test hypotheses of early hominin body size and limb proportions. Yet, no early hominin is as complete (>90%), as is the ∼3.67 Ma 'Little Foot' (StW 573) skeleton from Sterkfontein Member 2. Here, we provide the first descriptions of its upper and lower long limb bones, as well as a comparative context of its limb proportions. We found that StW 573 possesses absolutely longer limb lengths than A.L. 288-1, but both skeletons show similar limb proportions. This finding seems to argue against a purely allometric explanation for A.L. 288-1 limb proportions. In fact, our multivariate allometric analysis suggests that limb lengths of Australopithecus, as represented by StW 573 and A.L. 288-1, exhibit a significantly different (p < 0.001) allometric pattern than that which typifies modern humans and African apes. Like some previous analyses, our results also suggest that hominin limb evolution occurred in two stages with: first, a modest increase in lower limb length and a concurrent shortening of the antebrachium between Ardipithecus and Australopithecus, followed by a considerable lengthening of the lower limb along with a decrease of both upper limb elements occurring between Australopithecus and Homo sapiens.

A multiscale stratigraphic investigation of the context of StW 573 'Little Foot' and Member 2, Sterkfontein Caves, South Africa.

The Sterkfontein Caves is currently the world's richest Australopithecus-bearing site. Included in Sterkfontein's hominin assemblage is StW 573 ('Little Foot'), a near-complete Australopithecus skeleton discovered in Member 2 in the Silberberg Grotto. Because of its importance to the fossil hominin record, the geological age of StW 573 has been the subject of significant debate. Three main hypotheses have been proposed regarding the formation and age of Member 2 and by association StW 573. The first proposes that Member 2 (as originally defined in the type section in the Silberberg Grotto) started to accumulate at around 2.58 Ma and that the unit is contained within the Silberberg Grotto. The second proposes that Member 2 started forming before 3.67 ± 0.16 Ma and that the deposit extends into the Milner Hall and close to the base of the cave system. The third proposes a 'two-stage burial scenario', in which some sediments and StW 573 represent a secondary and mixed-age accumulation reworked from a higher cave. The stratigraphic and sedimentological implications of these hypotheses are tested here through the application of a multiscale investigation of Member 2, with reference to the taphonomy of the StW 573 skeleton. The complete infilling sequence of Member 2 is described across all exposures of the deposit in the Silberberg Grotto and into the Milner Hall. Sediments are generally stratified and conformably deposited in a sequence of silty sands eroded from well-developed lateritic soils on the landscape surface. Voids, clasts and bioclasts are organized consistently across and through Member 2 conforming with the underlying deposit geometry, indicating gradual deposit accretion with no distinct collapse facies evident and only localized intra-unit postdepositional modification. The stratigraphy and sedimentology of Member 2 support a simple single-stage accumulation process of Member 2 and a primary association between the sediments of Member 2 and the StW 573 'Little Foot' skeleton.

The bony labyrinth of StW 573 ("Little Foot"): Implications for early hominin evolution and paleobiology.

Because of its exceptional degree of preservation and its geological age of ∼3.67 Ma, StW 573 makes an invaluable contribution to our understanding of early hominin evolution and paleobiology. The morphology of the bony labyrinth has the potential to provide information about extinct primate taxonomic diversity, phylogenetic relationships and locomotor behaviour. In this context, we virtually reconstruct and comparatively assess the bony labyrinth morphology in StW 573. As comparative material, we investigate 17 southern African hominin specimens from Sterkfontein, Swartkrans and Makapansgat (plus published data from two specimens from Kromdraai B), attributed to Australopithecus, early Homo or Paranthropus, as well as 10 extant human and 10 extant chimpanzee specimens. We apply a landmark-based geometric morphometric method for quantitatively assessing labyrinthine morphology. Morphology of the inner ear in StW 573 most closely resembles that of another Australopithecus individual from Sterkfontein, StW 578, recovered from the Jacovec Cavern. Within the limits of our sample, we observe a certain degree of morphological variation in the Australopithecus assemblage of Sterkfontein Member 4. Cochlear morphology in StW 573 is similar to that of other Australopithecus as well as to Paranthropus specimens included in this study, but it is substantially different from early Homo. Interestingly, the configuration of semicircular canals in Paranthropus specimens from Swartkrans differs from other fossil hominins, including StW 573. Given the role of the cochlea in the sensory-driven interactions with the surrounding environment, our results offer new perspectives for interpreting early hominin behaviour and ecology. Finally, our study provides additional evidence for discussing the phylogenetic polarity of labyrinthine traits in southern African hominins.

Hominin vertebrae and upper limb bone fossils from Sterkfontein Caves, South Africa (1998-2003 excavations).

OBJECTIVES: We provide descriptions and functional interpretations of 11 >2.0 Ma hominin vertebral and upper limb fossils from Sterkfontein. MATERIALS AND METHODS: We employed taphonomic methods to describe postmortem damage observed on the fossils. We used osteometric tools and measurements to generate quantitative descriptions, which were added to qualitative descriptions of the fossils. These observations were then interpreted using published data on the same skeletal elements from extant and extinct hominoid taxa. RESULTS: Six of the fossils carry carnivore tooth marks. Two vertebrae show morphologies that are consistent with fully developed lordosis of the lumbar spine, but which are not completely consistent with bipedal loading of the same intensity and/or frequency as reflected in the lumbars of modern humans. A clavicle shows a combination of humanlike and apelike features, the latter of which would have endowed its hominin with good climbing abilities. When combined, analyses of fragmentary radius and ulna fossils yield more ambiguous results. DISCUSSION: The new fossil collection presents a mix of bipedal and climbing features. It is unclear whether this mix indicates that all Sterkfontein hominins of >2.0 Ma were terrestrial bipeds who retained adaptations for climbing or whether the collection samples two differently adapted, coeval hominins, Australopithecus africanus and Australopithecus prometheus, both of which are represented at Sterkfontein by skull remains. Regardless, the significant frequency of tooth-marked fossils in the sample might indicate that predation was a selection pressure that maintained climbing adaptations in at least some Sterkfontein hominins of this period.

The endocast of StW 573 ("Little Foot") and hominin brain evolution.

One of the most crucial debates in human paleoneurology concerns the timing and mode of the emergence of the derived cerebral features in the hominin fossil record. Given its exceptional degree of preservation and geological age (i.e., 3.67 Ma), StW 573 ('Little Foot') has the potential to shed new light on hominin brain evolution. Here we present the first detailed comparative description of the external neuroanatomy of StW 573. The endocast was virtually reconstructed and compared to ten southern African hominin specimens from Makapansgat, Malapa, Sterkfontein and Swartkrans attributed to Australopithecus and Paranthropus. We apply an automatic method for the detection of sulcal and vascular imprints. The endocranial surface of StW 573 is crushed and plastically deformed in a number of locations. The uncorrected and therefore minimum cranial capacity estimate is 408 cm3 and plots at the lower end of Australopithecus variation. The endocast of StW 573 approximates the rostrocaudally elongated and dorsoventrally flattened endocranial shape seen in Australopithecus and displays a distinct left occipital petalia. StW 573 and the comparative early hominin specimens share a similar sulcal pattern in the inferior region of the frontal lobes that also resembles the pattern observed in extant chimpanzees. The presumed lunate sulcus in StW 573 is located above the sigmoid sinus, as in extant chimpanzees, while it is more caudally positioned in SK 1585 and StW 505. The middle branch of the middle meningeal vessels derives from the anterior branch, as in MH 1, MLD 37/38, StW 578. Overall, the cortical anatomy of StW 573 displays a less derived condition compared to the late Pliocene/early Pleistocene southern African hominins (e.g., StW 505, SK 1585).

The Oldowan industry from Swartkrans cave, South Africa, and its relevance for the African Oldowan.

The oldest recognized artifacts at the Swartkrans cave hominid-bearing site in South Africa have long been known to occur in the Lower Bank of Member 1, now dated with the cosmogenic nuclide burial method to ca. 1.8-2.19 Ma. However, the affinities of this industry have been debated due to small sample size. In this paper we present newly excavated material from the Lower Bank retrieved since 2005 in the Swartkrans Paleoanthropological Research Project. The sample is now large enough to confirm its affinity with the Oldowan industrial complex. The assemblage is highly expedient and core reduction strategies are largely casual. Although freehand flaking is present, the bipolar technique is most significant, even in non-quartz raw materials. The Swartkrans assemblage shows some significant contrasts with the Sterkfontein Oldowan, ca. 2.18 Ma, which can be explained by its closer proximity to raw material sources, its somewhat different geographic context, and its more expedient nature. The Swartkrans Oldowan now provides us with the first good indication of Oldowan variability in southern Africa, where only two sizeable assemblages have thus far been discovered. Comparisons are made with other sites across Africa that help to place this variability within our overall understanding of the Oldowan industrial complex.

Cranial vault thickness variation and inner structural organization in the StW 578 hominin cranium from Jacovec Cavern, South Africa.

The Sterkfontein Caves site is one of the richest early hominin fossil localities in Africa. More specifically, the fossiliferous deposits within the lower-lying Jacovec Cavern have yielded valuable hominin remains; prominent among them is the Australopithecus partial cranium StW 578. Due to the fragmentary nature of the braincase, the specimen has not yet been formally assigned to a species. In this context, we employ microtomography to quantify cranial thickness and composition of StW 578 in order to assess its taxonomic affinity. As comparative material, we investigate 10 South African hominin cranial specimens from Sterkfontein (StW 505, Sts 5, Sts 25, Sts 71), Swartkrans (SK 46, SK 48, SK 49) and Makapansgat (MLD 1, MLD 10, MLD 37/38), attributed to either Australopithecus or Paranthropus, as well as 10 extant human and 10 extant chimpanzee crania. Thickness variation in and structural arrangement of the inner and outer cortical tables and the diploë are automatically assessed at regular intervals along one parasagittal and one coronal section. Additionally, topographic cranial vault thickness distribution is visualized using color maps. Comparisons highlight an absolutely and relatively thickened condition of the StW 578 cranial vault versus those of other South African Plio-Pleistocene hominins. Moreover, in StW 578, as well as in the Australopithecus specimens Sts 5 and Sts 71 from Sterkfontein, the diploic layer contributes substantially to cumulative vault thickness (i.e., >60%). Within the comparative sample investigated here, StW 505 and Sts 71 from Sterkfontein Member 4, both attributed to Australopithecus, most closely resemble StW 578 in terms of cranial vault thickness values, tissue proportions, and two- and three-dimensional distributions. Including additional Plio-Pleistocene Australopithecus and Paranthropus crania from South and East Africa in future studies would further help establish morphological variability in these hominin taxa.

Hominin skeletal part abundances and claims of deliberate disposal of corpses in the Middle Pleistocene.

Humans are set apart from other organisms by the realization of their own mortality. Thus, determining the prehistoric emergence of this capacity is of significant interest to understanding the uniqueness of the human animal. Tracing that capacity chronologically is possible through archaeological investigations that focus on physical markers that reflect "mortality salience." Among these markers is the deliberate and culturally mediated disposal of corpses. Some Neandertal bone assemblages are among the earliest reasonable claims for the deliberate disposal of hominins, but even these are vigorously debated. More dramatic assertions center on the Middle Pleistocene sites of Sima de los Huesos (SH, Spain) and the Dinaledi Chamber (DC, South Africa), where the remains of multiple hominin individuals were found in deep caves, and under reported taphonomic circumstances that seem to discount the possibility that nonhominin actors and processes contributed to their formation. These claims, with significant implications for charting the evolution of the "human condition," deserve scrutiny. We test these assertions through machine-learning analyses of hominin skeletal part representation in the SH and DC assemblages. Our results indicate that nonanthropogenic agents and abiotic processes cannot yet be ruled out as significant contributors to the ultimate condition of both collections. This finding does not falsify hypotheses of deliberate disposal for the SH and DC corpses, but does indicate that the data also support partially or completely nonanthropogenic formational histories.

Hominin hand bone fossils from Sterkfontein Caves, South Africa (1998-2003 excavations).

We describe eleven hominin metacarpals and phalanges recovered from Jacovec Cavern and Member 4 of the Sterkfontein Formation between 1998 and 2003. Collectively, the fossils date in excess of 2.0 Ma, and are probably attributable to Australopithecus africanus and/or Australopithecus prometheus. When combined with results of previous studies on Australopithecus postcranial functional morphology, the new data presented here suggest that at least some late Pliocene and/or early Pleistocene hominins from Sterkfontein were arboreally adept. This finding accords with the reconstruction of the site's >2.0 Ma catchment area as well-vegetated and containing significant woody components. In addition, most of the new specimens described here evince morphologies that indicate the hands from which they derived lacked complete modern humanlike manual dexterity, which is integral to the manufacture and use of intentionally shaped stone tools. The absence of lithic artifacts from both stratigraphic units from which the fossils were excavated is consistent with this conclusion.

New early Pleistocene hominin teeth from the Swartkrans Formation, South Africa.

We describe 14 hominin teeth and tooth fragments excavated recently from Swartkrans Cave (South Africa). The fossils derive from Members 1 (Lower Bank) and 3, from the Member 2/3 interface and from two deposits not yet assigned to member (the "Talus Cone Deposit" and the "Underground North Excavation" [UNE]) of the Swartkrans Formation, and include the first hominin fossil from the UNE, the two smallest Paranthropus robustus deciduous maxillary second molars in the entire hominin fossil record, and one of the smallest P. robustus permanent maxillary second molars from Swartkrans. The small permanent molar is accompanied by another tooth from a different individual but from the same stratigraphic level of the Swartkrans Formation; this second tooth is among, if not, the largest P. robustus permanent maxillary first molars known from anywhere-lending credence to assertions that degrees of body size sexual dimorphism previously ascribed to this species may be underestimated. It is more equivocal whether this evidence also supports hypotheses proposing that P. robustus assemblages from Swartkrans (as well as those from other South African cave sites) formed through the taphonomically biasing actions of large carnivores.

Earliest modern human-like hand bone from a new >1.84-million-year-old site at Olduvai in Tanzania.

Modern humans are characterized by specialized hand morphology that is associated with advanced manipulative skills. Thus, there is important debate in paleoanthropology about the possible cause-effect relationship of this modern human-like (MHL) hand anatomy, its associated grips and the invention and use of stone tools by early hominins. Here we describe and analyse Olduvai Hominin (OH) 86, a manual proximal phalanx from the recently discovered >1.84-million-year-old (Ma) Philip Tobias Korongo (PTK) site at Olduvai Gorge (Tanzania). OH 86 represents the earliest MHL hand bone in the fossil record, of a size and shape that differs not only from all australopiths, but also from the phalangeal bones of the penecontemporaneous and geographically proximate OH 7 partial hand skeleton (part of the Homo habilis holotype). The discovery of OH 86 suggests that a hominin with a more MHL postcranium co-existed with Paranthropus boisei and Homo habilis at Olduvai during Bed I times.

First partial skeleton of a 1.34-million-year-old Paranthropus boisei from Bed II, Olduvai Gorge, Tanzania.

Recent excavations in Level 4 at BK (Bed II, Olduvai Gorge, Tanzania) have yielded nine hominin teeth, a distal humerus fragment, a proximal radius with much of its shaft, a femur shaft, and a tibia shaft fragment (cataloged collectively as OH 80). Those elements identified more specifically than to simply Hominidae gen. et sp. indet are attributed to Paranthropus boisei. Before this study, incontrovertible P. boisei partial skeletons, for which postcranial remains occurred in association with taxonomically diagnostic craniodental remains, were unknown. Thus, OH 80 stands as the first unambiguous, dentally associated Paranthropus partial skeleton from East Africa. The morphology and size of its constituent parts suggest that the fossils derived from an extremely robust individual who, at 1.338±0.024 Ma (1 sigma), represents one of the most recent occurrences of Paranthropus before its extinction in East Africa.