Border Cave is an archaeological site located in the western Lebombo Mountains in Kwazulu-Natal. The rock shelter has one of the longest archaeological records in southern Africa, which spans from the Middle Stone Age to the Iron Age.
The west-facing cave is located about 100 m below the crest of the Lebombo mountain range. The variable rates of weathering of the Lebombo's Jurassic rocks led to the cave's formation.
Researchers have excavated at Border Cave since 1934. In chronological order, excavations occurred in 1934 (Raymond Dart), 1940 (W.E. Horton, non-scientific), 1941–1942 (Cooke, Malan and Wells), 1970–1975, and 1987 (Peter Beaumont). Lucinda Backwell and colleagues reopened the site in 2015, and are currently excavating and analyzing more archaeological materials. Researchers have used a combination of carbon-14 dating, amino acid racemisation, luminescence, and electron spin resonance to date the site's oldest deposits to ~250,000 years before present. Border Cave's remains include human remains, lithics, bone tools, botanical remains (i.e. grass bedding) and animal bones.
Border Cave's long occupational sequence makes the site an important location for studying prehistoric hunter-gatherer behavior and the causes and timing of the Middle to Later Stone Age transition. The site's human remains have led to debates on the timing of modern human origins in southern Africa. Some of the cave's other artifacts (i.e. bone points) have also played into researchers' debates on the origins of hunter-gatherer cultural adaptations and the appropriateness of ethnographic analogy in interpreting the archaeological record.
Regional setting
Border Cave is located at 27°01′19″S, 31°59′24″E within the Kwazulu region. The site is near the Eswatini/South Africa border at an altitude of 600 meters above sea level (masl). The mouth of the cave faces west over the Eswatini lowveld biome. The Jozini Rock Formation's Jurassic age rocks (182.1 ± 2.9 million years old) are the main types that make up the cave.
The main rivers near Border Cave include Usuthu, Ngwavuma, and Pongolo Rivers, which all flow from West to East. They all cut through the mountains and flow over horizontal beds of faulted rock. These rivers converge into Delagoa Bay. These rivers also erode certain areas of the Lebombo Mountains and cause differential weathering among the Karoo rocks (i.e. the Stormberg basalts and Ecca shales). Rhyolites, feldspar and quartz are common to the Border Cave region.
Modern environment
Current annual rainfall is approximately 820 millimetres (32 in) at the town Ingwavuma, which is roughly 12 kilometres (7.5 mi) south of Border Cave. The cave resides in a biodiversity hotspot called the Maputoland Center of Endemism, which has abundant riverine and lowveld vegetation. The specific vegetation zones that occur near Border Cave include Lebombo Summit Sourveld, and Northern and Southern Lebombo Bushveld. Vegetation surveys indicate that the main plants common to Border Cave include Androstachys johnsonii, Acacia spp., Combretum spp., Olea europaea subsp. africana, Canthium spp., Dichrostachys cinerea, Diospyros dichrophylla, Eretia rigida, Euclea divinorum, Euphorbia tirucalli, Maytenus spp., Eragrostis, Spirostachys africana, Strychnos henningsii and Vitex wilmsii.
Paleoenvironment Rodent and insectivore remains (primarily from Angoni vlei rat, pygmy mouse, and least dwarf shrew) suggest that Border Cave vegetation communities changed multiple times during the Late Pleistocene. These communities include miombo savanna woodland (heavily wooded environment, ~250,000–100,000 years BP), Zululand Thornveld (predominantly grasses, ~100,000–50,000 years BP), Mopane, and Lowveld/arid Lowveld (savanna woodland type environment, ~50,000–24,000 years BP). Annual rainfall was at least 25–100% higher during the miombo savanna woodland period than today, but less than 10% of rainfall occurred during the winter. The replacement of miombo woodland by Zululand Thornveld would have likely meant a 20% to 30% increase in precipitation, and a change to Lowveld would have meant a 15% decrease in precipitation. In sum, mean annual rainfall would have decreased from 200% of present-day rainfall to 60% of present-day mean annual rainfall from the beginning to end of Border Cave's sequence.
Excavation history Raymond Dart directed preliminary excavations at Border Cave in 1934. He dug an exploratory trench east–west trench close to Border Cave's entrance. Although Dart found Middle Stone Age artifacts, he did not publish any of his findings.
W.E. Horton dug at Border Cave in 1940, though only for agricultural purposes. Horton excavated for bat guano, and exposed artifacts and human remains in the process. However, he displaced these artifacts and remains from their original context and left his excavated sediment at the site (what some researchers call "Horton's Pit").
Cooke and colleagues re-excavated Horton's sediment during 1941–1942 and recovered the human remains. These remains included a partial adult cranium and other human remains fragments (individuals BC1 and BC2). Cooke and colleagues also discovered a mostly intact infant skeleton (BC3) at the site alongside some Conus shells.
Peter Beaumont excavated the site between 1970 and 1975. Beaumont, Todd and Miller jointly excavated more material in 1987. During these excavations, Beaumont and colleagues excavated two areas in the North and South parts of the cave.Beaumont, P. (1978). Border Cave [MA Thesis]. University of Cape Town. They recovered enamel samples from a human mandible (specimen BC5) for electron spin resonance dating. The sample returned a date of 74,000 ± 4,000 years BP. Beaumont analyzed the site's stratigraphy (consisting mostly of alternating Brown Sand and White Ash layers) and material culture (particularly the lithics) to a greater degree of detail than previous researchers. Beaumont suggested that four cultural layers at Border Cave existed, which included MSA 1 (Pietersberg), MSA 2b (Howiesons Poort), MSA 3 (post-Howiesons Poort) and ELSA (Early Later Stone Age).
Lucinda Backwell's team from the University of the Witswatersrand reopened the site in 2015 and are currently excavating more deposits. These current excavations have focused on redefining the excavation grid and determining precise proveniences of artifacts larger than 2 cm using a total station. The team is also trying to update faunal and lithic analyses of Border Cave's newly excavated material.
Site dating Researchers have used electron spin resonance and radiocarbon dating to date Border Cave's oldest deposits to 227,000 ± 11,000 years BP and the youngest deposits to 41,100–24,000 years BP. Luminescence dates extend the oldest age of the site to ~250,000 years BP, though the rest of these luminescence dates roughly align with the electron spin resonance and radiocarbon dates.
Paleoanthropological findings
Researchers have documented anatomically modern human remains from nine different individuals at Border Cave (BC1, BC2, BC3, BC4, BC5, BC6, BC7, BC8a, and BC8b), though researchers have lost the remains from four of those individuals (BC 6, BC 7, BC8a, and BC8b). Researchers have used electron spin resonance (ESR) to directly date some of these remains.
BC1 is an incomplete cranium that W.E. Horton found during his 1940 excavation. BC1's ages remains uncertain, though ESR returned dates of 77,000 ± 2,000 years BP and 161,000 ± 10,000 to 144,000 ± 11,000 years BP. Amelie Beaudet and colleagues' analysis of BC1 states that the cranial vault is similar in shape to anatomically modern humans, but also shares some traits in the bony labyrinth with fossil hominins such as Homo erectus (which are also found in modern humans but not in Neanderthals).
BC2 is a partial mandible from W.E. Horton's excavation. The provenance and date for this individual remain unknown.
BC3 is a nearly complete infant skeleton that Cooke and colleagues found in 1941. Cooke and colleagues found perforated Conus bairstowi shells with the infant, which likely came from the eastern Cape coast. Carbon-14 dating of the shell returned an age of ~ 33,570 ± 120 years BP. Some suggest that the infant burial represents one of the earliest southern African examples of burial ornamentation.
BC4 is an Iron Age skeleton with a missing skull. Researchers dated BC4 to 340 ± 45 years BP and 480 ± 45 years BP using radiocarbon dating.
BC5 is a nearly complete mandible that researchers dated to 74,000 ± 5,000 years BP with ESR.
Researchers lost BC6 (humerus), BC7 (proximal ulna) and BC8a and BC8b (two metatarsals), and lack adequate provenance information to accurately date these remains.
Archaeological findings
Middle Stone Age (MSA)
Botanical remains Border Cave preserves botanical remains dating back to ~227,000 years BP, which are older than those of previous findings in southern Africa (i.e. grass bedding from Sibudu Cave dating to 77,000 years BP). The oldest plant remains are grass beds from layers dating to 227,000-179,000 years BP. Panicoideae grasses, occasional sedges and dicotyledenous leaves make up the bedding. The grass beds are located near the rear of the cave. The burnt charcoal within the grass bedding and alternating stratigraphic layers of brown sand and white ash represent multiple burning events over time. Burn marks on Border Cave's grass bedding tend to only occur near the edges, rather than throughout the beds, which may indicate that these edges may have accidentally been burned. In total, there are 48 bedding layers. There are also Hypoxis rhizomes within Border Cave's hearths, which has led some to suggest that Border Cave's inhabitants cooked plants for food. Regular burning occurred by 170,000 years BP according to the phytolith record. Other phytolith remains include Chloridoideae and Pooideae grasses.
Lithics
Raymond Dart uncovered "Middle Stone Age" lithics in his preliminary excavations of Border Cave, though he did not formally analyze them. Peter Beaumont performed one of the first comprehensive lithic analyses of Border Cave's material, and he recognized two distinct stone tool industries for Border Cave's MSA layers: Howiesons Poort (HP) (from layers dating 81–65 kya) and MSA 3/post-Howiesons Poort (post-HP) (from layers dating 64–44 kya). Beaumont found many punched blades, backed pieces and triangular retouched pieces in the HP layers. The MSA 3/post-HP layers had very few backed pieces, and instead had more prepared cores.
Paloma de la Peña and colleagues later analyzed lithics from the same layers at Border Cave. A majority of these lithic raw materials were rhyolite or basalt, though quartz, chalcedony, agate and chert also occur within this assemblage. Backed pieces occur in the HP layers, but are absent in the MSA 3/post-HP layers. Other retouched tools such as notched pieces, and denticulates occur in the MSA 3/post-HP layers, though in lesser quantities.
The MSA 3/post-HP layers contain mostly unretouched triangular points. Lithic analysis suggests that hunter-gatherers used both Levallois and discoidal reduction techniques to produce these points. These points' morphologies (particularly the discoidal ones) are very different from one another, which has led some to believe that there was a lack of planning in lithic reduction strategies. Lucy Timbrell and colleagues hypothesize that the lack of retouch of the MSA 3/post-HP points may be due to low site occupation intensity, raw material abundance, point hafting requirements, or the sufficiency of unretouched tools in accomplishing tasks. This is in contrast with assemblages from other sites (i.e. Sibudu Cave), which preserve a greater abundance of retouch debris. Small platform bladelet cores and bipolar cores and flakes also occur in the MSA 3/post-HP layers.
Fauna