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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.

The Plio-Pleistocene site of Kromdraai B (South Africa), located in the ‘Cradle of Humankind’ area recognized in 1998 by UNESCO, corresponds to a Plio-Pleistocene paleokarst that yielded the holotype of Paranthropus robustus in 1938. Since that discovery, thousands of faunal remains (including additional hominin fossils) and stone tools have been discovered there. Here we report a new study of the karstic fillings of the hominin-bearing site of Kromdraai, which enables a reappraisal of its stratigraphy. The deposits correspond to a talus cone fed by one entrance that progressively filled the cave, which is larger than previously thought. Based on the stratigraphy, geometry, and composition of the breccias, we propose a new and more complex evolution of the cave. Four main periods of cave filling can be distinguished, corresponding to four kinds of deposits directly related to the evolution of the cave, and which show the progressive dismantling of the cavity and increasing influence from the landscape surface. This filling regime, however, is not continuous, and major unconformities identified may cover long periods of time. Despite this, an overall coherence emerges from the history of the cave and its deposits, the paleontological and paleoanthropological data, and the archaeological studies. It is now possible to reinterpret the discoveries from earlier investigations and place them in their general stratigraphic context. Our study shows that Kromdraai spans a much longer time span of hominin evolution than previously proposed. In addition, the breccias from the central part of the Kromdraai B site provide some of the first data on at least part of a hitherto unrecorded period at Sterkfontein: a phase marked by a major erosional unconformity between Members 4 and 5, before 2.20 Ma.

The Sterkfontein palaeokarst deposits, the richest repository of Australopithecus fossils in the world, are currently divided into six members (M1–M6) and named the Sterkfontein Formation ( Partridge and Watt, 1991 ). In this system, it was proposed that the passages and chambers deeper than the Silberberg Grotto formed most recently and are filled with comparatively young sediments from newer openings or reworked sediments from older, upper chambers. Here we describe the geomorphology, sedimentology, fauna and archaeological evidence from six deposits excavated near the base of the system in the Milner Hall. The use of a multidisciplinary approach enabled us to clarify the complex stratigraphic history, to track artefact-bearing deposits through multiple phases of deposition, and to identify an early deposit accumulated from the Silberberg Grotto to the base of the system. We propose that the Australopithecus -bearing Member 2 deposit originally extended down to near the base of the Milner Hall. We further propose that the vertical extent of the cave system was developed prior to the opening to the landscape surface, and that at that time the groundwater level was comparable to that seen now. We therefore argue that some of the earliest palaeoanthropological material in South Africa may have been deposited into the deepest chambers of the Sterkfontein Caves.

The Sterkfontein Caves, located in the southwest of the Cradle of Humankind, Gauteng, is the world’s richest Australopithecus-bearing locality and has yielded iconic fossils like Mrs Ples (StS 5) and Little Foot (StW 573), as well as Paranthropus robustus, Homo ergaster and Homo habilis fossils and large Earlier Stone Age lithic assemblages. The cave deposits have also yielded enormous assemblages of associated fossil fauna and document over three and a half million years of landscape, environmental, faunal and hominid evolution. These fossiliferous cave deposits represent a more recent episode of a geological history spanning 2.6 Ga years, beginning with the deposition of the dolomites, to the commercial exploitation of the caves by lime miners in the early twentieth century. The location and morphology of the karst caves is a result of a combination of factors including lithological variation within the two host dolomite formations, an early karstification and infilling of the dolomites over two billion years ago and local dolomite fracturing. Vadose zone collapse in densely fractured areas has enlarged chambers and passages, and played a major role in the location and nature of the openings to the landscape. When open to the landscape, a broad range of geomorphological processes, including re-dissolution of interred deposits, creates dynamic sedimentary environments with complex stratigraphic histories. This article reviews the geomorphological history of the Sterkfontein Caves in an effort to consolidate this information as we press forward with new stratigraphic and geomorphological work at the site.

The Sterkfontein Caves , located in the south-west of the Cradle of Humankind in Gauteng is the world’s richest Australopithecus -bearing locality. The fossil-bearing cave deposits represent a more recent instalment of a history spanning 2.6 Ga, from the deposition of the karst -hosting dolomite s, to the commercial exploitation of the caves by lime miners in the early twentieth century. The location and morphology of the caves is a result of lithological variation within the two host dolomite formations, multiple and complex phases of karstification and infilling of the resultant solution cavities over the two billion years since the dolomite deposition, and consistently active local tensional joint and fault systems. Where vadose collapse has opened the caves to the landscape, a broad range of geomorphological processes has created dynamic sedimentary environments with complex stratigraphic histories.

StW 573, Little Foot, is the most complete Australopithecus skeleton yet discovered, with many of its bones found in their correct anatomical position. Since the discovery of the in situ skeleton in the Silberberg Grotto in 1997, several teams have attempted to date the fossil. This appeared a simple process because several flowstones are inter-bedded in the breccia above and below StW 573. Dating of these flowstones, using U–Pb (uranium-lead) isotope decay techniques, gave younger results than expected from the fauna and stratigraphic position, around 2.2 Ma (millions of years). Our recent stratigraphic, micromorphological and geochemical studies revealed that the stratigraphy is much more complicated than was previously thought, with localized post-depositional processes leading to the creation of voids within the breccia around the skeleton. These voids were then filled by multiple generations of flowstone growth. The research we present here demonstrates that the proposed dates based on the flowstone deposition can give only a minimum age for StW 573 and that the flowstone formation came after, and probably long after, the breccia deposition. If one takes account of the long evolution of these karst fillings, StW 573 appears to be significantly older than 2.2 Ma.

The depositional history of the Name Chamber at the Sterkfontein early hominid site is complex, as is the case with most such cavities. Unravelling this history may therefore benefit from the input of less usual lines of evidence to complement baseline geological investigations. In this case, micromammalian remains from the Western Talus of the Name Chamber provide tentative evidence for the depositional history of these deposits. Correlation of samples based on minimum numbers of individuals referred to genera occurring in one third or more of the samples suggests that a large proportion of the Western Talus material, particularly that from the area infiltrated by the Eastern Talus deposit, originated in the vicinity of squares P54, Q54 and Q55 in the main excavation, from a depth spanning the boundary between Acheulean and Oldowan levels in Member 5. Differences in general diversity between the samples from the main excavation and some from the Name Chamber support the proposal that surface sediments of the homogeneous deposits have been contaminated by material entering the cavern during the 1994 opening of the feeder shaft. Initial taphonomic analysis indicates that all samples, both the original and those from the Name Chamber, were accumulated by the same avian predator, that is, one or more of three owl species (barn owl Tyto alba, grass owl Tyto capensis and marsh owl Asio capensis).

Significance Here we present evidence of hominin locomotor behavior from the trabecular bone of the femur. We show evidence for habitual use of highly flexed hip postures, which could potentially indicate regular climbing in a South African hominin from Sterkfontein, which is either Paranthropus robustus or Homo. Second, we present evidence that Australopithecus africanus likely did not climb at the frequencies seen in extant nonhuman apes, and exhibits a modern, human-like pattern of loading at the hip joint. These results challenge the prevailing view of a single transition to bipedalism within the hominin clade by providing evidence of climbing in a more recent, non-Australopithecus South African hominin, and add to the increasing evidence for locomotor diversity in the hominin clade., Bipedalism is a defining trait of the hominin lineage, associated with a transition from a more arboreal to a more terrestrial environment. While there is debate about when modern human-like bipedalism first appeared in hominins, all known South African hominins show morphological adaptations to bipedalism, suggesting that this was their predominant mode of locomotion. Here we present evidence that hominins preserved in the Sterkfontein Caves practiced two different locomotor repertoires. The trabecular structure of a proximal femur (StW 522) attributed to Australopithecus africanus exhibits a modern human-like bipedal locomotor pattern, while that of a geologically younger specimen (StW 311) attributed to either Homo sp. or Paranthropus robustus exhibits a pattern more similar to nonhuman apes, potentially suggesting regular bouts of both climbing and terrestrial bipedalism. Our results demonstrate distinct morphological differences, linked to behavioral differences between Australopithecus and later hominins in South Africa and contribute to the increasing evidence of locomotor diversity within the hominin clade.

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