Journal articles on the topic 'Karst – South Africa – Sterkfontein Caves'

South Africa is a country of great fascination to those interested in the origins, development and behaviour of humankind. For example, recent fossil discoveries appear to confirm Darwin's hunch that Africa – and perhaps southern Africa – was the cradle of humankind. Caves in the Sterkfontein Valley near Johannesburg have produced abundant scientific information on the evolution of modern man over the past 3.5 million years. This is of interest not only from a historical point of view but also in terms of modern science. With the significant advances in medical genetics in general, and psychiatric genetics in particular, there has been a growing interest in homogeneous populations with novel gene pools. South Africa is a rich source of homogeneous populations with an apparently common ancestry.

Abstract A water level rise of almost 3 m in the space of two years in the Sterkfontein Cave system since late-2009 necessitated the re-routing of the tourist path through the cave to successively higher elevations on three occasions. It also raised concern for a possible association with copious acidic and sulphate-rich mine water drainage from the West Rand Goldfield (a.k.a. Western Basin) starting in early-2010, and the related threat to the UNESCO-inscribed fossil site. Although these circumstances have had little impact on the tourist value of the site, a prognosis of the impact on cave water level and quality is indicated by virtue of its karst setting and palaeontological significance. Historical and recent potentiometric data, together with ancillary hydrogeological and hydrochemical information acquired in the course of a water resources monitoring programme for the broader Cradle of Humankind World Heritage Site, provides new insight into the hydrogeology of the cave system. An improved understanding of the hydrophysical and hydrochemical response of the cave water system sheds light on the location of this system within the water resources environment. It is proposed that the present-day maximum cave water level is constrained to an elevation of ~1440 m above mean sea level. The recent electrical conductivity of 78 mS/m for cave water is 32% greater than the 59 mS/m recorded in mid-2010 and earlier. Similarly, the recent sulphate concentration of 161 mg/L is 178% greater than the 58 mg/L recorded before 2010. Compared to coeval values for ambient karst groundwater represented by the normative Zwartkrans Spring water, the magnitude of the increases in the springwater are similar, viz. 48% (from 84 to 124 mS/m) in salinity and 166% (from 154 to 409 mg/L) in sulphate. Although a distinct mine water impact is evident in both instances, the values indicate a muted impact on the cave water chemistry compared to the springwater. These and other documented observations better inform the threat from various poorer quality water sources to the fossil site in particular, and to the broader karst water resource in general. This contextualises concern for the hydroenvironmental future of Sterkfontein Cave and other nearby fossil sites such as Swartkrans, Rising Star and Bolt’s Farm. The dynamic response of the water resources environment to a variety of hydrological and hydrogeological drivers reinforces the need for monitoring vigilance across a range of disciplines.

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.

The paraphyletic group of Old World rock gecko genus Cnemaspis, currently comprises ~180 described species from Africa and Asia. The south-east Asian clade with 63 described species, is most diverse on the Thai-Malay Peninsula, with just five species known from Borneo, an island biodiversity hotspot. Karst regions are known as centres for species endemism, and vast areas of caves and karst exist across northern Borneo. Fieldwork from 2017 to 2020 recovered additional undescribed species of Cnemaspis from areas of karst forests in western and northern Sarawak. These discoveries emphasize the importance of preserving areas of limestone karst within rainforest areas for maintaining species diversity, as well as accelerating research on documenting the biota.

Abstract Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized caves resulted from generalized dissolution of silicate formations in spite of their low solubility. Karstification is produced by deep hydrous transfer along lithological discontinuities and fracture net works. The existence of such caves has major implications in geomorphology, under either Sahelian and Equatorial climate, and in hydrogeology and water supply, particularly in the Sahel area. Introduction. – Since a few decades, several karst-like morphologies are described in non-carbonated rocks (sandstones, quartzites, schistes, gneisses…) [Wray, 1997 ; Vicat and Willems, 1998 ; Willems, 2000]. The cave of Guéssédoundou in West Niger seems to be due to a large dissolution of metagabbros. The cave of Mfoula, South Cameroon, attests for the same process in gneisses. This forms proof that big holes may exist deeper in the substratum even of non-carbonated silicate rocks. Their size and number could mainly influence the landscape and the hydrogeology, especially in the Sahelian areas. Guéssédoundou, a cave into metagabbros in West Niger. – The site of Guéssédoundou is located 70 km south-west of Niamey (fig. 1). The cave is opened at the top of a small hill, inside in NNE-SSW elongated pit (fig. 2 ; pl. I A). The hole, 3 to 4 m deep and 20 m large, has vertical walls and contains numerous sub-metric angular blocks. A cave, a few meters deep, comes out the south wall. Bedrocks consist of metagabbros of the Makalondi greenstone belt, a belt of the Palaeoproterozoic Birimian Formations of the West Africa craton [Pouclet et al., 1990]. The rock has a common granular texture with plagioclases, partly converted in albite and clinozoisite, and pyroxenes pseudomorphosed in actinote and chlorite. It is rather fairly altered. Chemical composition is mafic and poorly alkaline (tabl. I). A weak E-W schistosity generated with the epizonal thermometamorphism. The site depression was created along a N010o shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation. The absence of human activity traces and the disposition of the angular blocks attest that the pit is natural and was due to the collapse of the roof of a vast cavity whose current cave is only the residual prolongation. To the vertical walls of the depression and at the cave entry, pluridecimetric hemispheric hollows are observed (pl. I B). Smooth morphology and position of these hollows sheltered within the depression dismiss the assumptions of formation by mechanical erosion. In return, these features are typical shape of dissolution processes observed into limestone karstic caves. That kind of process must be invoked to explain the opening of the Guéssédoundou cave, in the total lack of desagregation materials. Dissolution of metagabbro occurred during hydrous transfer, which was probably guided by numerous fractures of the shear zone. Additional observations have been done in the Sirba Valley, where similar metabasite rocks constitute the substratum, with sudden sinking of doline-like depressions and evidence of deep cavities by core logging [Willems et al., 1993, 1996]. It is concluded that karstic phenomena may exist even in silica-aluminous rocks of crystalline terrains, such as the greenstones of a Precambrian craton. Mfoula a cave into gneisses in South Cameroon. – The cave of Mfoula is located 80 km north-east of Yaoundé (fig. 3). It is the second largest cave of Cameroon, more than 5,000 m3, with a large opening in the lower flank of a deep valley (pl. I C). The cavity is about 60 m long, 30 m large and 5 to 12 m high (fig. 4; pl. I D). It is hollowed in orthogneisses belonging to the Pan-African Yaoundé nappe. Rocks exhibit subhorizontal foliation in two superposed lithological facies: the lower part is made of amphibole- and garnet-bearing layered gneisses, and the upper part, of more massive granulitic gneisses. Average composition is silico-aluminous and moderately alkaline (tabl. I). The cave is made of different chambers separated by sub-cylindrical pillars. The ceiling of the main chamber, 6 m in diameter, is dome-shaped with a smooth surface (D, fig. 4). The walls have also a smooth aspect decorated with many hemispherical hollows. The floor is flat according to the rock foliation. They are very few rock debris and detrital fragments and no traces of mechanical erosion and transport. The general inner morphology is amazingly similar to that of a limestone cave. The only way to generate such a cavity is to dissolve the rock by water transfer. To test the effect of the dissolution process, we analysed a clayey residual sampled in an horizontal fracture of the floor (tabl. I). Alteration begins by plagioclases in producing clay minerals and in disagregating the rock. However, there is no more clay and sand material. That means all the silicate minerals must have been eliminated. Dissolution of silicates is a known process in sandstone and quartzite caves. It may work as well in gneisses. To fasten the chemical action, we may consider an additional microbial chemolitotrophe activity. The activity of bacteria colonies is known in various rocks and depths, mainly in the aquifer [Sinclair and Ghiorse, 1989 ; Stevens and McKinley, 1995]. The formation of the Mfoula cave is summarized as follow (fig. 5). Meteoric water is drained down along sub-vertical fractures and then along horizontal discontinuities of the foliation, particularly in case of lithological variations. Chemical and biological dissolution is working. Lateral transfers linked to the aquifer oscillations caused widening of the caves. Dissolved products are transported by the vertical drains. Regressive erosion of the valley, linked to the epeirogenic upwelling due to the volcano-tectonic activity of the Cameroon Line, makes the cavities come into sight at the valley flanks. Discussion and conclusion. – The two examples of the Guéssédoundou and Mfoula caves evidence the reality of the karsts in non-carbonated silicated rocks. The karst term is used to design ≫ any features of the classical karst morphology (caves, dolines, lapies…) where dissolution plays the main genetical action ≫ [Willems, 2000]. Our observations indicate that (i) the karst genesis may have occurred into any kind of rocks, and (ii) the cave formation is not directly dependent of the present climate. These facts have major consequences to hydrogeological investigations, especially for water supply in Sahelian and sub-desertic countries. Some measurements of water transfer speed across either sedimentary pelitic strata of the Continental terminal or igneous rocks of the substratum in West Niger [Estèves and Lenoir, 1996 ; Ousmane et al., 1984] proved that supplying of aquifers in these silico-aluminous rocks may be as fast as in a karstic limestone. That means the West Niger substratum is highly invaded by a karstic net and may hidden a lot of discontinuous aquifers. The existence of this karst system can be easily shown by morphological observations, the same that are done in karstic limestone regions (abnormally suspended dry valleys, collapses, dolines…). Clearly, this must be the guide for any search of water, even in desertic areas where limestones are absent.

Pickering et al. (Nature 2018;565:226–229) utilised calcium carbonate flowstone deposits (i.e. speleothems) from eight Pliocene and Pleistocene South African Cradle of Humankind cave sites to propose that biases were created within the fossil record due to absent clastic sedimentation phases during wet periods, when caves were closed and only speleothems accumulated. Such a scenario has significant implications for our understanding of variability in hominin mobility, resource exploitation, functional repertoires and interactions with competitors in changing environmental and ecological contexts. We find considerable issues with the article. First, Pickering et al.’s contribution omits crucial fossil evidence from various stratigraphic units of the Sterkfontein Caves that indicates conditions were not always arid when the caves were open and sediments were deposited. Second, Pickering et al.’s proposa that clastic and speleothemic deposits (including faunal and floral material) form mutually exclusively is an overly simplified, binary depositional (and in this case environmental) framework that demonstrates an inherent bias in the sampling of cave deposits for dating. This creates the impression that either speleothems or clastic sediments are deposited and does not take into account the full spectrum of sedimentary complexity in karst caves. Third, closure of the caves across the Cradle of Humankind landscape during wet periods is not substantiated geomorphologically or speleologically; identification of the responsible process is critical to the proposed infilling scenario.

We describe late Pliocene and early Pleistocene hominin fossils from Sterkfontein Caves (South Africa), including two femoral specimens, as well as a partial tibia and a partial fibula. The fossils are likely assignable to Australopithecus africanus and/or Australopithecus prometheus and the morphology of each corroborates previous interpretations of Sterkfontein hominins as at least facultative bipeds.

Abstract First ribs – the first or most superior ribs in the thorax – are rare in the hominin fossil record, and when found, have the potential to provide information regarding the upper thorax shape of extinct hominins. Here, we describe a partial first rib from Member 4 of the Sterkfontein Caves, South Africa. The rib shaft is broken away, so only the head and neck are preserved. The rib is small, falling closest to small-bodied Australopithecus first ribs (AL 288-1 and MH1). Given that it was recovered near the StW 318 femur excavation, which also represents a small individual, we suggest that the two may be associated. Three-dimensional geometric morphometric analyses were used to quantify the rib fragment morphology and compare it to extant hominoid and other fossil hominin ribs. While only the proximal end is preserved, our analyses show that South African Australopithecus share derived features of the proximal first rib more closely resembling A. afarensis and later hominins than great apes.

The Sterkfontein Caves site is one of the richest early hominin localities in Africa. In addition to significant fossil assemblages from Members 2 and 4 of the Sterkfontein Formation, recent excavations have revealed hominin-bearing sedimentary deposits in the lesser-known Milner Hall. We describe two hominin cranial fragments excavated from the Milner Hall in 2015 and present the results of a high-resolution microtomographic-based approach to diagnosing the anatomical and taxonomical origin of these specimens. Based on external morphology, StW 671 and StW 672 are tentatively identified as frontal and occipital fragments, respectively. Our non-invasive bi-dimensional quantitative investigation of the two cranial fragments reveals a mean cranial thickness of 8.8 mm and 5.6 mm for StW 671 and StW 672 respectively and a contribution of the diploic layer to the cumulative cranial thickness that is less than 50%. While the mean cranial thickness of StW 671 falls within the range of Homo, the relative proportion of the diploë in both StW 671 and StW 672 is lower than in Australopithecus (>60%) and extant humans (>50%). Accordingly, in terms of both cranial thickness and inner structural organization, the Milner Hall hominins combine derived and unique traits, consistent with the condition of other postcranial and dental material already described from the deposit. Moreover, our study opens interesting perspectives in terms of analysis of isolated cranial fragments, which are abundant in the hominin fossil record. Significance: The Sterkfontein Caves have widely contributed to our understanding of human evolution. Besides the well-known Members 4 and 2, where the iconic ‘Mrs Ples’ and ‘Little Foot’ have been found, in this study we suggest that the Milner Hall locality represents an additional, stratigraphically associated source of not only fossil hominins, but also Oldowan stone tools. In particular, we describe for the first time two cranial fragments, StW 671 and StW 672, identified as frontal and occipital bones, respectively. Our microtomographic-based analysis of these materials reveals some affinities with Homo combined with unique characters. In this context, our study suggests an intriguing mosaicism consistent with the description of the two fossil hominins found in the Milner Hall.

Abstract We present the first application of high-resolution micro computed tomography in an analysis of both the internal and external morphology of the lumbar region of StW 431 – a hominin skeleton recovered from Member 4 infill of the Sterkfontein Caves (South Africa) in 1987. The lumbar vertebrae of the individual present a number of proliferative and erosive bony processes, which were investigated in this study. Investigations suggest a complex history of taphonomic alteration to pre-existing spinal degenerative joint disease (SDJD) as well as post-mortem modification by an unknown insect. This study is in agreement with previous pathological diagnoses of SDJD which affected StW 431 and is the first time insect traces on this hominin are described. The results of this analysis attest to the complex series of post-mortem processes affecting the Sterkfontein site and its fossil assemblages.

The site of the Sterkfontein Caves, South Africa, is one of the richest early hominin fossil-bearing sites in Africa. Recent excavations in the Milner Hall locality have contributed to the discovery of new hominin specimens, including StW 669, a right permanent maxillary first molar (M1). StW 669 was excavated from the T1 deposits, which consist of a mixture of sediments from Members 2 and 5 of the Sterkfontein Formation. Accordingly, the deposits have the potential to contain remains of Australopithecus, Paranthropus and Homo. In this study, we employed micro-focus X-ray tomography in order to assess dental tissue proportions, enamel thickness distribution and enamel-dentine junction morphology as approaches to investigate the taxonomy of StW 669. We compare our results to those generated on the teeth of Australopithecus africanus, Paranthropus robustus, Homo erectus, Homo antecessor, Homo neanderthalensis and Homo sapiens. Our results suggest that StW 669 shares quantitative and qualitative affinities with M1s of Homo in terms of tissue proportions (i.e. two- and three-dimensional average and relative enamel thickness of 1.2–1.3 mm and 18.4, respectively) and enamel thickness distribution (i.e. thickest enamel on the lingual aspect of the protocone). However, data on the enamel-dentine junction morphology of StW 669 are inconclusive as to the tooth’s taxonomic affinities. Pending additional morphometric analyses, our studies of inner morphology of the crown of StW 669 support its attribution to Homo.

The Bakwena Cave houses a variety of organisms that form an intricate and interdependent food web. This cave is utilised as a permanent roost by a colony of Natal clinging bats. The bat guano and allochthonous plant material that fall into the cave from outside, form the basis of the ecology inside the cave which may be considered a typical example of a detritus ecosystem. Decomposers such as bacteria and fungi are responsible for the decay of the guano and plant detritus which, in turn, are utilised by several organisms, including nematodes and mites, as food source. These animals form the next trophic level which is utilised by predatory arthropods as food source. The Bakwena Cave is one of the few dolomitic caves in South Africa that provide access to the water table. The groundwater houses several types of organisms, including bacteria, fungi and animals – primarily nematodes and crustaceans. The Bakwena Cave is also the type locality for freshwater amphipods in Southern Africa. This unique and sensitive ecosystem is primarily dependent on bat guano. The grassland surrounding the cave is utilised by the bats as foraging area and is currently threatened by urban development and the resulting habitat fragmentation and destruction. A cascade of extinctions of the cave-dwelling organisms will follow if the bats abandon the cave.