  Bolt's Farm Location in Gauteng | |
| Location | Gauteng Province, South Africa |
|---|---|
| Coordinates | 26°02′00″S27°42′43″E / 26.033235°S 27.712057°E /-26.033235; 27.712057 |
| Part of | Cradle of Humankind |
| Area | 1.3 km2 (0.50 sq mi) |
| History | |
| Periods | Early Pliocene,Plio-Pleistocene,Late Pleistocene,Holocene |
Bolt's Farm is apalaeontological site in theCradle of Humankind World Heritage Site,Gauteng province, South Africa. With more than 30 fossil deposits dating back 4.5 Ma, it is one of the oldest sites currently discovered in the Cradle of Humankind. It consists of multiple cavities, pits, and quarries, where caves have eroded away, exposing theirfossiliferous interiors. Although this site has not yet yielded thehominid fossils for which the Cradle of Humankind is known, Bolt's Farm is still an important source of fossils from various species ofEarly Pliocene andPlio-Pleistocene fauna, includingprimates andbig cats.
Bolt's Farm is located about 3 km (1.9 mi) southwest of theSterkfontein archaeological site and is located in the southwestern corner of theCradle of Humankind World Heritage Site. The site is carved out of the Malmani Subgroup of theTransvaal Supergroup, which formed during thePalaeoproterozoic era around 2.6–2.4 billion years ago under what was then aninland sea.[1]
The pockmarked appearance of the area is the result of heavy ancient cave erosion down to the floors and walls of the passages, resulting in dozens ofdolomite solution cavities andpalaeokarst pits that have preserved fossils inbreccia,speleothem,sandstone, andsiltstone. These deposits occur over a 1.3 km2 (0.50 sq mi) stretch of hillside.[1][2][3] It is unknown if these caves were once interconnected and contemporary with one another, or if they existed separately. The oldest of these deposits yet known is Waypoint 160, which was discovered in 1996 and has been dated back to theEarly Pliocene, approximately 4.5–4 Ma.[4][2] Almost all other sites have been dated back only to thePlio-Pleistocene; dates vary from one pit to the next, although most fall in the range of 2–1 Ma. One site, New Cave, may hold fossils that are significantly more recent; remains there have been dated to theLate Pleistocene into theHolocene.[5]
Palaeontological studies of the fossils recovered at the site seem to suggest that, at the time the site was active, the region was drier and the area was more open than it is today.[6] Nevertheless, the site is believed to have been in relative proximity to a water source.[7] The species recovered from Bolt's Farm and the greater Sterkfontein Valley area may have inhabited a range of local habitat types, ranging from covered forest to open grasslands. Browser and grazer species, as well as ground and tree-dwelling primates, are represented in the fossil record.[8][4] At least one location on the site dated to 2–1.5 Ma, Pit 23, has been theorised to have been a "death trap" where ancient fauna inadvertently fell to their deaths and their remains were preserved over time.[5]
The area on the northern edge of a farm owned by Billy Bolt, for whom the site is named, was first used as aspeleothem quarry during the late 19th and early 20th centuries. Miners harvested this speleothem for use inlime production. This process unearthed fossil deposits, which were first sampled and examined by palaeontologistRobert Broom during a 1936 expedition to Transvaal. Broom named many of the fossiltaxa recovered from the site.[9] In 1947 and 1948, a team of researchers from theUniversity of California Museum of Paleontology (UCMP) led by palaeontologistsFrank Peabody andCharles Lewis Camp, called theUniversity of California Africa Expedition, began exploring palaeontological sites across eastern and southern Africa. A team of the southern branch of the expedition led by Peabody was responsible for the first excavation at Bolt's Farm.[5] The mining had created rubble chunks containing fossiliferousbreccia; early investigations retrieved material from this rubble, instead of mining itin situ. Additionally, the UCMP excavations were centred on the main quarry. Multiple smaller excavations have been completed in the decades since. Historically, Bolt's Farm has been ignored for sites wherehominid fossils have already been discovered, which are of much more interest to archaeologists; thus, the study of the site has lagged behind that of its neighbors likeSterkfontein.[1][2]
Until the 1990s, the precise locations of multiple fossiliferous pits within the larger site were poorly recorded and thus unable to be located by subsequent archaeologists. Renewed surveying began in the 1990s has attempted to rediscover the deposits first described in—but barely explored since—the 1940s. In the process, these surveys have unsurprisingly uncovered new sites. In 1991, Basil Cooke published the first updated map of the site since the 1940s excavations; however, attempts to line up Peabody's original map and site descriptions with sites identified in more recent surveys remain a source of confusion for researchers.[9] However, Cooke's survey marked the beginning of a period of renewed interest in Bolt's Farm. A survey done by French researchers from 1996 to 1999 revealed new fossil species and sites, including Waypoint 160, which is thought to be the oldest known site in the Cradle of Humankind.[1][2] A survey done by the Cradle of Humankind's Human Origins and Past Environments Research Unit (HRU) team between 2008 and 2011 identified 23 old sites and eight new ones.[3] Further surveys carried out in the late 2010s have usedGIS andaerial drone surveying to more accurately identify these sites.[9]
Some of the specimens collected during the 1940s excavations have been lost; however, many of those surviving are stored at theUniversity of California Museum of Paleontology at theUniversity of California, Berkeley. Beginning in the late 1950s, loans andrepatriation efforts have handed over many of the fossils to theEvolutionary Studies Institute at theUniversity of the Witwatersrand inJohannesburg.[10] TheDitsong National Museum of Natural History inPretoria is also in possession of Bolt's Farm specimens, where many are kept on semi-permanent display to the public.[11]
Fossils recovered from the Bolt's Farm pits represent a wide array ofmacrofauna. Animals active in the Bolt's Farm area during thePlio-Pleistocene includedbig cats, non-hominidprimates, snakes, horses,mustelids,bovids, pigs,antelope,rodents,jackals, reptiles, andbirds of prey. Signs of variousmicrofauna have also been uncovered but not studied in-depth.[2]
The deposits have also yielded some of the oldest primate fossils in the Cradle of Humankind; they belong toParapapio (specifically,Pp. broomi andPp. whitei), extinct species of baboons that have also been located atSterkfontein,Taung, andMakapansgat. ThePp. whitei specimens from Bolt's Farm are the most complete remains of this species that have been discovered.[12][6] Other primate remains includeTheropithecus,Papio robinsoni andCercopithecoides williamsi.[13][14] Because hominid fossils contemporary to the depositional period have been recovered in similar conditions in east African archaeological sites, several researchers have put forth the suggestion that hominid fossils could be found at Bolt's Farm as well.[1]
Other species represented in the Bolt's Farm fossil deposits areAntidorcas recki,Ictonyx bolti,Metridiochoerus andrewsi,[15]Euryotomys bolti,Elephantulus antiquus,[16]Boltimys broomi,[10] andProteles cristatus.[17] Bolt's Farm has yielded some of the best specimens ofPlio-Pleistocene big cats in South Africa, including a complete skull and jaw of the saber-toothed catDinofelis barlowi.[13] The first fossil remains of a snake belonging to the familyElapidae recovered from southern Africa were collected from Bolt's Farm in 2009.[18] The 2016 discovery at Bolt's Farm of the first fossilAgama lizard recovered from the Cradle of Humankind was announced in 2020.[19]
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