Saturday 31 July 2021

Searching for dental caries in South African fossil Hominins.

Dental caries (the formation of cavities in teeth through decay of the enamel, through the activities of Bacteria) is common in many modern Human populations, and is generally associated with a diet rich in plant-derived foods rich in sugars and starches. The presence of widespread dental caries in Human populations is generally thought to have come about during the Neolithic, when the cultivation of grains was adopted, providing a source of food reliable enough to allow populations to rise and more complex cultures to develop, but at the same time exposing people to the hazards of a starch-rich, grain-based diet. If this is the case, then instances of dental caries should be relatively rare in Pleistocene Humans, as well as in other Hominin species. 

Modern dental caries is generally associated with the Bacterium Streptococcus mutans, which thrives in the mouths of people with restricted diets, and less diverse oral microbiotic ecosystems, and which is thought to have become particularly prevailent since the industrial revolution. However, a wide range of Bacteria can cause such damage, and in some cases combinations of Bacteria, which in themselves do little damage, can cause problems. Notably, different types of damage are associated with different Bacterial species, or combinations thereof. Damage is typically caused by Bacteria producing acids which the saliva cannot buffer, resulting in erosion of the tooth material. Some foodstuffs are particularly prone to causing caries, notably products with high levels of refined carbohydrates and sugars, but also some natural foods such as fruits, honey, and some nuts and seeds. Instances of carries are far lower in people with diets rich in tough fibrous foods, which promote saliva formation, as well as diets rich in seafood or meat.

Environmental and genetic factors also appear to play a role in the prevalence of dental caries, although it is unclear how. Different populations with similar diets are known to have different rates of dental caries, although the causes of this are unclear. Instances of caries are well known in both archaeological and fossil dental collections, with the varying prevalence of the condition in different agricultural populations fairly well studied. The condition is also known to affect non-Human Primates, with captive populations more affected than wild populations.

In a paper published in the South African Journal of Science on 29 March 2021, Ian Towle of the Sir John Walsh Research Institute at the University of Otago, Joel Irish of the Research Centre in Evolutionary Anthropology and Palaeoecology at Liverpool John Moores University, and the Evolutionary Studies Institute and Centre for Excellence in PaleoSciences at the University of the Witwatersrand, Isabelle De Groote of the Department of Archaeology at Ghent University, Christianne Fernée of the Department of Anthropology and Archaeology at the University of Bristol, and the Department of Archaeology at the University of Southampton, and Carolina Loch, also of the Sir John Walsh Research Institute at the University of Otago, present the results of a study in which they analysed a range of South African Hominin fossils in the collections of the University of the Witwatersrand and Ditsong National Museum of Natural History, including samples of the recently discovered Homo naledi

Towle et al. only examined whole teeth, and only considered cases where cavities were clearly present to be evidence for caries; instances of discolouration were considered insufficient evidence due to the nature of the material. Specimens were initially examined with a hand lens, and damage was rated from (1) to (4), using the scheme: (1) enamel destruction only; (2) dentine involvement but pulp chamber not exposed; (3) dentine destruction with pulp chamber exposed; and (4) gross destruction with the crown mostly affected. Finally the location of damage on each tooth was recorded as distal, buccal, occlusal, lingual, mesial, root, or a combination thereof.

The degree of wear (physical abrasion) to each tooth was also recorded, in order to examine the corelation between diet and caries, and to give an estimate of the age of the individuals from which the teeth came (and therefore the age at which they were becoming affected by caries). The front teeth were given a simple wear score from one to eight, with the molars split into four quadrants, each of which was given a wear rating of between one and ten, with an average being used for the whole tooth. Comparisons were made between teeth rather than between individuals, as the majority of the material was in the form of loose teeth, although Towle et al. do recognise that there is a possibility of multiple teeth from the same locarion coming from the same individual, and that it is likely that an individual with caries on one tooth would have it on others.

A subset of the affected teeth were further subjected to computerised tomography scanning at the Department of Human Evolution of the Max Planck Institute for Evolutionary Anthropology, which can differentiate between dentine and enamel, as well as detecting cases of caries where the affected area has reduced density but not obvious cavities. 

Prior to Towle et al.'s work, six cases of dental caries had been identified in Hominin specimens from South Africa, and Towle et al. were able to add another four examples to this; two from specimens of Paranthropus robustus, and two from a single individual of Homo naledi. A total of fourteen examples of caries have now been found in ten teeth from seven Homininss. The seven individual Hominins in which dental caries have been diagnosed comprise five Paranthropus robustus, one Homo naledi, and one 'early Homo'. No evidence if dental caries has been found in any example of Australopithecus sediba or Australopithecus africanus.

One of the previously described specimens, SK 15 (early Homo) interproximal caries on the lower right second molar and left first molar. (a) Overview of specimen; scale bar is 1 cm. (b) Mesial carious lesions (white arrows) and (c) close-up of the right second molar with carious lesion on the mesial surface. Towle et al. (2021).

Homo naledi specimen UW 101-001 shows the worst case of caries ever described in a non-Human Hominin. The cavities present penetrate deep into the dentine, and appear to have been active for a long time. There is no difference in the wear on the teeth affected, suggesting the cavities were not having an impact on mastication function. The cavities are present on the right fourth premolar and first molar, on the surface where these teeth would have faced one-another, implying they had a common cause. In the case of the molar the cavity has expanded to cover much of the occlusal surface, and affected both the root and crown of the tooth. There is sediment present on the surface of the tooth, which accumulated after death, preventing an investigation into how deep the cavity had penetrated into the dentine, and whether it had reached the pulp chamber; it was not possible to subject this specimen to computerised tomography.

UW 101-001 (Homo naledi) carious lesions on the lower right second premolar (distal) and first molar (mesial). (a) Overview of specimen; white arrow shows location of the two interproximal carious lesions; scale bar is 1 cm; (b) Close-up of lesions. (c) Right second and third molars, with two antemortem chips on the mesial buccal corner (white arrow). Towle et al. (2021).

Paranthropus robustus mandible SK 23 also shows occlusal caries on two teeth, in this case the left first molar and right second premolar. Both these teeth show large, dark cavities, though again this is partially covered by a matrix of material that had accumulated post-mortem. This sample did not prove particularly amenable to computerised tomography, although the area under the cavities did appear to be less dense, which would support a diagnosis of dental caries. 

SK 23 (Paranthropus robustus). (a) Occlusal view of mandible, with the lesion on the right second premolar highlighted (black arrow). (b) Closeup of the occlusal surface of the right second premolar. (c)  Computerised tomography reconstruction with the position of the two slices highlighted. (d) Computerised tomography slice toward the lingual part of the cavity. (e) Computerised tomography slice toward the buccal portion of the cavity. Towle et al. (2021).

The number of reported cases of dental caries in non-Human Hominins is low, but represents a significant proportion of the available specimens; 1.36% of all Homo naledi specimens, 1.75% of all Paranthropus robustus specimens, and 4.55% of all 'early Homo' specimens. Four of the seven specimens in which the condition is seen had more wear on the occlusal surfaces of the teeth than the average for such teeth, which may be significant, although most had close to the species average wear levels, and little damage to the crown.

SKX 5023 (Paranthropus robustus) lower right first molar. (a) Overview of specimen with carious lesion on the mesial surface (white arrow). (b) Close-up of mesial lesion. (c) Occlusal view of the specimen. (d) Occlusal/mesial view of specimen showing the carious lesion, antemortem chip (white arrow) and cupping dentine wear (white star). Both scale bars are 1 cm. Towle et al. (2021).

These results suggest that caries may have been more common in pre-agricultural populations than has generally been assumed, and that the condition was relatively common in some South African Hominins, and therefore presumably in Hominins in general. In modern dentistry, visual diagnosis is generally backed up with X-rays, physical probing, and observation of colour changes in teeth, but taphonomic changes make these approaches less useful in palaeontological and archaeological material. Towle et al. were able to examine a small number (five) of specimens by computerised tomography, with mixed results, and it will be necessary to apply this method to more specimens in order to judge how useful in can be.

DNH 40 (Paranthropus robustus) upper left third molar. (a) Overview of the tooth, showing mesial and occlusal surfaces (carious lesion indicated by white arrow); scale bar is 1 cm. (b) Close-up of mesial lesion. (c) Computerised tomography slice of the specimen; white arrow indicates the carious lesion. Towle et al. (2021).

Bacteria capable of causing caries appear to have been a problem for many, possibly all, Hominin species. This is consistent with recent work which suggests a wide range of Bacteria are capable of causing such damage, either on their own or in concert with other species; in the latter case the Bacteria involved may otherwise be a part of a normal, non-pathological, oral biota. This suggests that the major cause of dental caries is not, in fact the type of Bacteria, but rather the diet of the individual, which in turn implies that we can make judgements about the diets of extinct Hominins by the presence and prevalence of dental caries, although differing oral microbiomes in different Hominin species may have made them more, or less, vulnerable to dental caries under similar conditions. 

Caries on the occlusal surfaces of teeth is not associated with high rates of tooth loss, whereas caries on the interproximal surfaces (surfaces that face other teeth) is. Interproximal caries is often associated with the accumulation of plaque in these areas, which does not appear to be a factor in any of the South African Hominins. Enamel hypoplasia (poor formation of the enamel during development) is another major cause of vulnerability to dental caries, and may have been a factor in the cases of the Paranthropus robustus specimens SK 55 and SK 13/14, both of which show substantial hypoplastic pitting; something common in this species.

Dental caries may also develop as a response to damage or unusual wear patterns, which may create weaknesses in the tooth enamel, or spaces in which Bacteria can accumulate safely, and Towle et al. note that this appears to be present in several of the specimens in which they detected the condition. 

Chewing on hard items, such as grit in food, can cause damage to teeth which leaves them vulnerable to infection. In Hominins, the interproximal areas of teeth appear to be particularly prone to such damage, unlike in modern Humans, where the occlusal surfaces of the rear teeth are most affected, although the reason for this is unclear.

Modern Human samples, from the last 50 000 years, show levels of caries similar to that detected by Towle et al.; this changes with the adoption of agriculture, and in some populations becomes far more common. An infection rate of 1-5% seems to have been typical for both pre-Human Hominins and Humans leading hunter-gatherer lifestyles. Therefore, the occurence of caries appears to be strongly linked to behaviour and diet, rising in agricultural societies, but also in hunter-gatherer societies with certain diets.

The absence of dental caries observed in Australopithecus africanus is unlikely to reflect a radically different oral microbiome. Instead, this may be a result of a different diet, or simply sampling bias. The presence of the condition in Paranthropus robustus, Homo naledi, and 'early Homo' indicates that these species were consuming foods which made them vulnerable to the condition. Dental caries is also fairly common in species assigned to the genus Homo from elsewhere (including Neanderthals), suggesting that members of the genus have eaten dangerous foods (such as tubers, nuts, plants or fruit) since they first appeared.

See also...

Online courses in Palaeontology. 

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter


Friday 30 July 2021

Interpretting the Neolithic Mustatils of northwestern Arabia.

The northwestern part of the Arabian Peninsula was, until fairly recently, believed to have been largely uninhabited until the onset of the Iron Age, in the twelfth century BC. However, recent research has suggested that the area may have been inhabbited for much longer, by peoples with unique cultural identities not seen elsewhere. This research has identified thousands of stone structures across northwestern (and other parts of) Arabia, which have become collectively known as the 'Works of Old Men', and which date from the Middle Holocene (6500-2800 BC) onwards. These structures come in a range of forms, including burrial cairns, tower tombs, 'pendant' tombs, megalithic structures, monumental Animal traps (or 'kites'), and a variety of open-air structures.

One of the forms of open-air structure commonly found in the region is the mustatil (مستطيل), large rectangular structures ('mustatil' is Arabic for 'rectangle'), which comprise two long, parallel walls 20-640 m in length, with two short walls or platforms making up the other sides of the rectangle. Additional dividing long walls are sometimes present, giving the structures the appearance of a European farm gate; they were originally termed 'Gates', but this description has been dropped as it was somewhat confusing. Around 1000 of these structures have now been discovered, scattered across an area of about 200 000 km², between latitudes of 22.989° and 28.064° north and longitudes of between 36.875° and 42.700° west, with the highest concentrations in AlUla and Khaybar counties.

Following a preliminary report in 2017, the Royal Commission for AlUla comissioned the Aerial Archaeology in the Kingdom of Saudi Arabia AlUla project to carry out a survey of the mustatil structures of AlUla County, as part of the Identification and Documentation of the Immovable Heritage Assets of AlUla programme. This was later joined by a second project, Aerial Archaeology in the Kingdom of Saudi Arabia Khaybar, concentrating on the mustatils of Khaybar County. These projects have used publicly available satellite images to identify mustatil structures in remote areas, followed by a series of helicopter surveys, with 1072 mustatils identified from satellite images, 276 photographed from the air, and 39 surveyed from the ground. Several of the mustatils visited were subject to preliminary excavations, revealing features that were not previously known.

In a paper published in the journal Antiquity on 30 April 2021, Hugh Thomas, Melissa Kennedy, Matthew Dalton, Jane McMahon, David Boyer, and Rebecca Repper, all of Classics and Ancient History at the University of Western Australia, present the results of these initial surveys of the mustatils of AlUla and Khaybar counties, Saudi Arabia.

Mustatil distribution across north-western Arabia. Thomas et al. (2021).

Northwestern Saudi Arabia has exposures of three major geological sequences; the Precambrian volcanic and sedimentary sequences of the Arabian Shield, a sequence of Cambrian-Ordovician sandstones, and a series of Cainozoic basalts, associated with the formation of the Red Sea, as the Arabian Peninsula rifted away from Africa. These different rock-types determine the geomorphology of the region, and therefore the distribution of its archaeological sites.

The largest landforms are in areas where the Cambrian-Ordovician sandstones have been eroded by water to form canyons and mesas. In drier areas, the landscape becomes progressively less varied, as wind erosion takes over from water erosion, till in desert areas there is an essentially flat, sandy landscape, with scattered yardangs (wind-eroded rocky outcrops), often with flattened hilltops, and blackened by desert varnish (a coating of fused clay and manganese particles that forms on rock surfaces not subject to water-erosion).

A group of three mustatils. Thomas et al. (2021).

The Cainozoic Harrat Basalts also form extensive landscapes, notably the Harrats Khaybar, Kura and Ithnayn lavafields, and the Harrat Uwayrid basalt plateau north-west of AlUla. The oldest of these lavafields are Miocene in age, and have flat or gently undulating flow surfaces with few clay pans, while younger, Pliocene-Early Holocene examples form hummocky, ‘whale-back-style’ terrains, with large clay-filled depressions and localised higher relief around volcanic vents. 

Mustatils are found on all these landscapes, but their placement and form varies with landscape type.

All Mustatils are distinguished by the presence of a head, courtyard, and base, but some also associated with other features, such as orthostats (standing stones) and circular cells.

The head of a mustatil, note the chamber in the centre of the platform. Thomas et al. (2021).

The head of a mustatil typically comprises a dry-stone platform, rectangular or sub-rectangular in shape, 10-50 m in length, and 30-120 cm high. These were made from flat slabs of sandstone where these were available, but otherwise chunks of the local rock stacked together. In most of the investigated mustatils, a single oval or rectangular chamber, ranging in size from 2.8 x 2.8 m to 10 x 3 m, was present at the centre of the head. In some cases a doorway, less than 50 cm wide, connected this chamber to the main courtyard. In some instances this doorway had been deliberately blocked off, either with a single capstone or a pile of smaller stones, possibly when the site was decommissioned. Some of the chambers also have other features, notably niches.

Features of mustatil: (A) internal niche located in the head of a mustatil; (B) a blocked entranceway in the base of a mustatil; (C)–(D) associated features of a mustatil: cells and orthostats; (E) stone pillar identified on the Harrat Khaybar lava field. Thomas et al. (2021).

The courtyards of mustatils were rectangular, elongate areas, bounded by the head, the base, and the long walls. These appear to have been open spaces when in use; some examples have other structures within the courtyard area, such as smaller enclosures or funerary structures, though these are thought to post-date the original usage.

The long walls comprise two rows of laid stones filled with a rubble core. The laid stones were arranged either horizontally or vertically, with only a single example showing a mixture of horizontal and vertical stones. These walls varied between 50 cm and 3 m in width, and from 30 cm and 120 cm in height.

The base of the mustatils typically had an entrance 30-80 cm in width (sometimes slightly wider), directly opposite the central chamber in the head. Some of these entranceways also appear to have been blocked when the sites were decommissioned, sometimes symbolically with a few stones on either side, sometimes with the entire entrance being infilled.

Aerial image of three mustatil bases. Note the associated features (cells and orthostats) and blocked entranceways. Thomas et al. (2021).

Sixty five of the 109 sites surveyed from the ground or air had circular cells in front of their bases. These could be discrete, or interlocking, with each site having between three and eight such structures; although the number may actually be higher, as at many sites these have been partially covered by wind-blown sand. At sites with discrete cells, these cells are 1-2 m in diameter, and tend to all be the same size at any given site. At sites with interlocking cells the outermost cells tend to be 1.0-1.3 m in diameter, with the cells increasing in size progressing inwards, so that the largest, inermost cells are 1.8-2.0 m in diameter. These cells are aranged parallel to the base of the mustatil, with a passageway thus formed between the cells and the entrance to the courtyard. In five of the examined mustatils, these passageways had also been blocked, either deliberately or by collapse of the structures. At seven of the examined sites, the cells contained central orthostats (standing stones), fashioned from local stone and 1-1.5 m in height.

The mustatils surveyed on the Harrat Khaybar lava field differed slightly from mustatils surveyed elsewhere, in that they lacked orthostats, but instead had pillars of carefully stacked local stone, probably relating to a lack of suitable marterial to make true orthostats. These pilars occurred in clusters, with up to 50 seen at a single site.

The initial survey of the mustatil sites noted that many had associated 'I'-shaped structures, which have subsequently been shown to comprise low, rubble-filled platforms with an exterior face. These are quite variable in form, varying from structures that are distinctly 'I'-shaped to simple rectangular forms; the variation in shape in these structures closely aligns with variations in the shape of mustatils, with the two structures sharing a similar distribution range, although 'I'-shaped structures are less common, Similar rectangular structures are also known from southern Jordan, although it is unclear if these are related.

(A)–(B) I-type platforms; (C)–(D) rectilinear platforms. Thomas et al. (2021).

A total of 131 'I'-shaped structures have been recorded, of which 73 are adjacent to a larger mustatil. These are typically parallel to the mustatil, and aligned with either the base or a long wall. Up to six 'I'-shaped structures can be associated with a single mustatil, with the 'I'-shaped structures varying in size from 16 x 7 m to 42 x 16 m. These structures never cut across mustatils, and never use stone recycled from them, suggesting that they were in use at the same time, and, therefore, where the two are placed side-by-side, they were somehow functionally related. 

The examined mustatils vary considerably in form and shape, but have some consistent feature. Thomas et al. propose they be subdivided into two broad types; 'simple' mustatils with roughly rectangular shapes defined by a head, a base and two long walls, with may-or-may not have an entranceway in the base, but usually lack it, and 'complex' mustatils, which are similar in form, but always have an entrance, which is associated with other structures, such as circular cells and orthostats or pillars. They further note that the 'I'-shaped structures are only ever found in association with complex mustatils.

(A) ‘Simple’ mustatil; (B)–(C) ‘complex’ mustatils, single (B) and double (C). Thomas et al. (2021).

However, variations are present in both types of mustatil. Notably, additional long walls dividing the courtyard may be present in either simple or complex foems, Most mustatils appear to have been built in a single phase of construction, although some show signs of later modification. Bith simple and complex mustatils are found across the entire range of the structures, with their distribution apparently being random within this range.

The majority of mustatils are built upon exposed bedrock. They do not appear to be oriented towards any particular object or direction, but instead follow the local topography, somthing that varies greatly across the area, depending on the local geology. Where mustatils are built upon slopes, it is always with their long access perpendicular to the slope, while mustatils located on narrow sandstone ridges are arranged to allow the maximum length. On flat ground mustatils show no preferential orientation.

Geographic positioning of different mustatils. Thomas et al. (2021).

Where possible, the head of mustatils appears to have been deliberately places higher than the rest of the structure, something especially true of mustatils located on the rocks of the Precambrian Shield., but less marked on exposed sandstone outcrops, where the entire structure is typically located on a flat mesa surface. Arranging the mustatils in this way would have been more difficult on the younger volcanic terrains, but even hear these structures are often clustered around vents, enabling the head to be highest. emphasising how important this arrangement must have been. The majority of 'I'-shaped structures and rectangular platforms are also built on slopes. Mustatils placed upon hillslopes are visible from a great distance, which may have been the intention of such placement; those placed upon flat mesas above the wider plain are effectively hidden from sight, but themselves command excellent views. It therefore seems likely that visibility of and from the mustatils was important to their builders in some way.

Mustatils are often found clustered together, with up to 19 individual mustatils found in groups where none is further than 500 m from its neighbour. The mustatils of the Harrat Khaybar are more concentrated into groups than elsewhere, but this phenomenon is found across the entire geographical range of these structures. The reasons for this are unclear, though Thomas et al. suggest that a better understanding of the chronology of the sites construction and use might prove enlightening.

Excavations at the IDIHAF-0011081 mustatil site in eastern AlUla County have revealed a central chamber at the head in which a number of horns and skull fragments from Cattle, Sheep, Goats, and Gazelles have been placed around a central upright stone in the centre of the chamber. These remains are dominated by Cattle, and are assumed to have been some form of ritual sacrifice. No Human remains were found at the site, nor any signs of domestic occupation. Radiocarbon dates were obtained from a tooth and horn, which suggests that the animals from which these came were alive in the sixth millennium BC (Late Neolithic).

Artefacts recovered during excavation and ground survey: (A) Cattle horn positioned in front of a betyl (standing stone) at IDIHA-F-0011081; (B)–(C) cattle horns recovered from IDIHA-F-0011081; D) Neolithic micro core collected from IDIHA-F-0003301; (E) Neolithic bifacial foliate identified at IDIHA-F-0011394. Thomas et al. (2021).

A sample of charcoal that was obtained from a looted mustatil located to the south of the Nefud Desert produced a late sixth to early fifth millennium BC radiocarbon date, and faunal remains similar to those from the one excavated by Thomas et al. The type, and positioning, of these remains strongly suggests that the mustatils had a ritual purpose, as does the prominence of the mustatils in the landscape. This is supported by the fact that no mustatil investigated to date has produced any sign of occupation, and absence of any indication of any mustatil having ever been roofed. Orthostats have also been found at other sites in Arabia interpreted as having been used for ritual purposes, which again supports the idea that this was the purpose of the mustatils. The narrow entrances and elongate structures of the mustatils suggest that the rituals carried out within them may have been of a processionary nature, with participants moving in single-file from the entrance to the head.

Stone tools were found at four of the 39 mustatils investigated on the ground. These include a flaked micro core, an obsidian bifacial foliate, and some non-diagnostic flakes and debitage. However, most of the courtyards were devoid of any tools or other cultural material.

Mustatils are commonly found in association with other structures, including, funerary monuments and 'kites'. A total of 118 such associations were found in the aerial surveys, with the mustatils often being overbuilt by, or structurally robbed to build, the other structures. This implies that the mustatils are older than these other structures, and apparently the oldest structures in the area. In some cases, one mustatil appears to overlie another.

There are no known Human burials of similar age to the mustatils in northwestern Arabia. However, many later tombs are closely geographically associated with mustatils, including ringed tombs, with and without pendant tails. These 'pendant' tombs have been dated to between the fourth millennium BC and the second century AD, again supporting the idead that these structures were built after the mustatils, and that in some instances material was looted from mustatils to help build them.

Five examples of mustatils being overlain by 'kite' structures, and one, possible example of a mustatil overlying a 'kite'-structure. Kite structures are again thought to be fourth-to-third millennium BC in age, making them Neolithic in age, although more work needs to be done on these structures.

In all cases mustatils have been built from readily available local stone, which has affected the construction methods used, as well as the appearance and durability. Sandstone tends to split along bedding planes due to natural processes, forming a natural flagstone rock. A similar effect can be obtained using metamorphic schists, which are common in parts of the Precambrian Arabian Shield. In both cases the rock can be extracted in sheets by hand or using wooden tools. This will yield both flagstones from which walls can be made and larger rocks which can be placed upright to produce orthostats. Many of the rocks used in the construction of the mustatils are such sheets, with examples exceeding 500 kg in weight not unusual. Where walls are made from such flagstones they can be fitted together tightly, and are resilient to collapse, unlike walls made from more rounded stones, such as those available on basalt terrains.

The largest Mustatil that Thomas et al. surveyed on the ground was located on the Harrat Khaybar lava field, 50km south of the town of Khaybar. This is 525 m long and made from basalt boulders. Assuming that basalt has a density of 2500 kg/m³, Thomas et al. estimate that the construction of this site would have required the moving of 12 000 tonnes of rock, with the individual rocks used weighing from 6 to 500 kg.

Methods of estimating the amount of time and labour needed to construct stone monuments have been developed by archaeologists working on Mayan structures in the New World, and there were applied by Thomas et al. to the mustatils. This led them to conclude that a group of ten people could construct a 150 m mustatil in twe-to-three weeks, and that a 500 m mustatil could be built by a team of fifty people in about two months. Thus, most of the mustatils could have been built by small groups of workers in a relatively short period of time, and even the largest could have been constructed by a family group in a few months, and potentially much less time if several family groups worked together. The construction of mustatils could, therefore, have formed part of a broader Neolithic development of community and power structures, and possibly served as a means of maintaining social cohesion amoungst widely dispersed and/or nomadic pastoralist communities.

Understanding why the mustatils were built requires a wider understanding of the culture that produced them. They appear to date entirely from the Late Neolithic, and possibly represent a new culture moving into the area, as climatic variations in Arabia during the Late Pleistocene and Ealy Holocene are thought to have driven repeated colonisation of, and withdrawal from, areas by different Neolithic peoples, resulting in distinctive regional cultures across the landmass. The relationship between the mustatil-building culture and the Holocene Humid Phase (roughly 8000–4000 BC) is unclear.

The ritually deposited Cattle remains at site IDIHA-F-0011081 appear to represent the oldest known evidence for Cattle on the Arabian Peninsula, and therefore the arrival of an important economic resource for Neolithic pastoralists. Cattle are important in rock art from the Arabian Late Neolic, but the earliest known evidence for Cattle comes from Shi’b Kheshiya in Yemen, where there are a number of structures thought to have been associated with Cattle, and dates to about 4400 BC, making it about 900 years younger than site IDIHA-F-0011081.

The large size of the mustatils, and the way in which their makers were able to construct to a common plan over a very wide area, suggests that these structures were imoportat the their makers, and conveyed some connection with the land, possibly serving as terrirory boundaries, or sites of some ritual right of passage. On other parts of the peninsula, burial structures may have served a similar function,

No structures closely resembling mustatils are known from anywhere else, although a number of large, rectangular, open-air 'sanctuaries' are known from the Negev Desert, and these also date to the sixth millennium BC. However, while these share the same basic form as the mustatils, they show no similarity in placement or building methodology, making it unclear if there is any relationship. What the mustatils do appear to be is one of the first examples of a strictly ritual structure in the Neolithic of the Near East.

Mustatils are found across a wide area of northwestern Arabia, showing a remarkable level of structural conservatism, albeit with adjustments for local geology. Understanding the context in which these structures were built is clearly highly important for understanding the developing cultures of the Middle Holocene in the area, and the number of these monuments may indicate that this landscape may have supported a far higher population at this time than was previously thought.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter


Saturday 17 July 2021

Trouble in Myanmar: The worrying case of Burmese Amber.

Cretaceous ‘Burmese Amber’ has been extensively worked at several sites across northern Myanmar (though mostly in Kachin State) in the last 20 years. The amber is fairly clear, and often found in large chunks, providing an exceptional window into the Middle Cretaceous Insect fauna, as well as preserved examples of small Vertebrates, feathers from Birds and other Dinosaurs, and even the only known Ammonite preserved in amber. However, the trade in amber from Myanmar has raised deep concerns, as has the wider nature trade in gemstones from the country, due to the deteriorating Human rights situation in the country, and the highly exploitative working conditions at many mines there. Most noatably, in 2017 the Myanmar military seized direct control of the region, forcing many local residents (who were accused of being supporters of the Kachin Independence Army) to flee, and bringing in new workers from other parts of the country.

In April 2020 Emily Rayfield, Jessica Theodor, and David Polly of the Society of Vertebrate Paleontology sent a letter to the editors of over 250 scientific journals, raising concern about the trade in amber from Myanmar, Human rights abuses within the country, the ongoing conflict situation in the region, and the blurring of the distinction between public and private collections that had occurred in some journals with regard to material from the region (in order for a study to be published in a journal, the material involved should be held in a collection that has a predetermined policy on the making of material available to other researchers, such as a museum or university collection, rather than in private ownership).

Flowers preserved in amber from Kachin State, Myanmar. Myanmar Amber Museum.

This was followed in May 2020 by an editorial published in the Journal of Systematic Palaeontology in which editors Paul Barrett and Zerina Johanson, stated that that journal would no longer be publishing articles based wholly or in part upon amber from Myanmar, whether newly collected or from historic collections, citing concerns about working conditions at mines in Myanmar, the use of money obtained from the sale of amber and other gemstones to by arms and fund conflicts in the region, and the widespread illegal removal of amber from the country.

The issue has been addressed again in the June 2021 issue of the journal Nature Ecology and Evolution, with an editorial and a series of articles by scientists with views on the topic.

In the first of these papers, a group of scientists led by Chao Shi of the College of Marine Science and Biological Engineering at Qingdao University of Science and Technology and the Key Laboratory for Plant Diversity and Biogeography of East Asia at the Kunming Institute of Botany, argue that while the Human rights situation in Myanmar is now severe enough to justify a ban on the use of new specimens from the country in published scientific studies, a great deal of this material is already present in musuem and university collections around the world, and that it would be unreasonable to exclude this material from future studies.

A mining camp in a forest in Kachin State in 2010. Blood Amber/Kachin Development Networking Group.

In the second paper, Zin-Maung-Maung-Thein of the Department of Geology at the University of Mandalay, and Khin Zaw of the Centre of Ore Deposits and Earth Sciences at the University of Tasmania, raise concerns about Burmese Amber as a focus for 'parachute science', a term which refers to the practice of scientists from wealthy countries 'parachuting' into less well-off nations, collecting data or materials, then returning to their home nations to work on this material, without any benefit to the host nation, and often with scientists from that nation henceforth hampered from accessing the data or materials, due to their new location, and the high cost of accessing published information in many journals and other publications (ironically, this article is itself paywalled, and cannot be accessed without a subscription to Nature Ecology and Evolution, unless a fee is paid (US8.99 for the one-page article). In the case of Myanmar, amber is typically extracted then sold overseas, where it may be worked on by local scientists who are acting in good faith, but who in so doing are excluding scientists in Myanmar from accessing the same material. A study by Emma Dunne of the University of Birmingham and Nussaïbah Raja-Schoob of Friedrich-Alexander-Universität Erlangen-Nürnberg, and presented by Emma Dunne at a meeting of the Palaeontological Association in 2020, found that not a single publication on Burmese Amber in the English language published in the last 30 years included a local collaborator, whereas articles on Cainozoic Primates from Myanmar often did (suggesting that there is a local interest in palaeontology, and scientists in Myanmar who would be willing to work with with outside scientists). Dunne and Raja suggest that this difference may be because of the difference in status between amber and other fossils in Myanmar; in theory fossils are treated as antiquities in Myanmar, and a special permit is needed to export them, but amber is a 'gemstone' and may be exported without a permit (the export of gemstones, such as jade, rubies, and amber is a major earner of hard currencies for Myanmar). Zin-Maung-Maung-Thein and Khin Zaw suggest that scientists outside Myanmar wishing to work on this material should contact the government of Myanmar for permission, as well as museums and universities in the country to seek local collaborators.

In the final paper, Paul Barrett, Zerina Johanson and Sarah Long of the Natural History Museum again visit the dual legal nature of fossils in Burmese Amber, pointing out that the current situation is a 'legal quagmire' which researchers should contemplate very carefully before entering.

Finally, the editorial piece, having considered these issues, lays out the current policy for the publication of studies based upon material from Myanmar (or other troubled or contentious areas), across all Nature journals; to whit that the export of material must be in line with both local and international law, and that any material used in such studies should be deposited in a recognised museum, collection or accessible repository. 

The tip of the wing of a fledgeling Cretaceous Bird, trapped in Burmese Amber. Ming Bai/Chinese Academy of Sciences.

Whilst this editorial policy would seem to go some way towards addressing the problems of Burmese Amber, it by no means resolves all the issues raised within the articles. Notably, the number of publications featuring material from Burmese Amber has been rising sharply since 2010, and in particular since 2017, when the Myanmar military is reported to have taken over the amber-producing mines, and news of Human rights abuses associated with the mines began to emerge. Thus, one of the major concerns about Burmese Amber is behaviour of the ruling military junta, which is accused of both abusing the rights of miners, and of using money from the sale of amber to buy arms and fund conflicts against minority groups within Myanmar. This cannot be addressed by complying with Myanmar's export laws, since those laws are drawn up by, and serve the interests of, those accused of committing Human rights abuses. 

Neither can the problem of parachute science be resolved simply by making sure that specimens are in collections where they are (in theory) available to scientists from their home country. No matter how good the intentions of such countries, the cost of travelling to them in order to study material is often prohibitively expensive, particularly if more than one country needs to be visited to see scattered specimens. This is compounded by an increasing tendency by governments in Europe and North America to refuse to allow researchers from other parts of the world to enter their countries at all, something which plays well with sections of the western media that have taken to scapegoating immigrants at every opportunity, but which compounds the injustice of having material removed from countries to be studied in other parts of the world.

See also...

Online courses in Palaeontology. 

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

Monday 12 July 2021

Hunting preferences in Chimpanzees, and their implications for early Human hunters.

Chimpanzees, Pan troglodytes, are one of our closest non-Human relatives (along with Bonobos, Pan paniscus), sharing 96% of our genome, and many behavioural traits. Due to this, Chimpanzee behaviour is often used as a proxy for early Hominid behaviour (Hominids being Humans, and anything more closely related to Humans than it is to Chimpanzees and Bonobos). Chimpanzees were for a long time thought to be herbivorous, but the numerous studies of these Apes carried out since the 1960s have shown them to be omnivores, which actively hunt a wide range of prey, including smaller Primates, Chimpanzees are now known to engage in cooperative group hunting using a range of stone tools, which makes understanding this aspect of their behaviour particularly intriguing to scientists trying to understand the origins of such behaviours in Hominids.

The optimal foraging theory predicts that an Animal will chose prey that provides the maximum energetic return from capturing and consuming it without getting injured in the process. Chimpanzees are particularly interesting in this regard, as different groups of Chimpanzees favour different types of prey, and use different tools and hunting techniques, traits which are identified as evidence for the development of distinct cultures among different groups. Notably, many Chimpanzees live in areas where there is a marked seasonal variation in prey availability, requiring them to switch hunting techniques while still accessing the best available prey. This is predicted to be the largest size of prey that can be captured safely by Chimpanzees in any area at any given time, with Chimpanzee cultural traits evolving to maximise this return. Meat derived from hunts is divided among the group, with the first choice of meat usually going to the most mature members of the group, thereby promoting collaboration within the group over solitary hunting.

A Chimpanzee consuming an Ashy Red Colobus Monkey, Piliocolobus tephrosceles, in the Kibale National Park, Uganda. BBC Earth.

In a paper published in the journal Ecology and Evolution on 4 May 2021, Cassandra Bugir of the Conservation Biology Research Group at the University of Newcastle, Thomas Butynski of the Eastern Africa Primate Diversity and Conservation Program, and Matt Hayward, also of the Conservation Biology Research Group at the University of Newcastle, and of the Mammal Research Institute at the University of Pretoria, and the Centre for African Conservation Ecology at Nelson Mandela University, present the results of a study in which they searched the existing literature on Chimpanzee diet and behaviour in order to determine prey preferences amongst different Chimpanzee groups, and the factors which drove their prey selection choices.

Bugir et al. sought out data on both the prey type selected by Chimpanzees, and abundance data on the prey being taken, excluding from their study previous research where this was not provided and could not otherwise be determined. They were particularly interested in the prey species taken, the availability of those prey species, the number of each type of prey taken, the type of tools used to capture the prey, and the size and sex ration of hunting groups, and size of the prey in kilograms.

In some cases data on prey bodyweights were not available, but it was possible to estimate this from other studies of the prey species. The mean adult bodyweight of a male Chimpanzee was estimated at 41.2 kg, based upon data from previous studies, which was used as the standard against which prey bodyweight could be compared, as adult male Chimpanzees are the members of the group which do the most hunting.

Bugir et al. found a total of thirteen usable studies from four different localities, two in Uganda and two in Tanzania, and covering the period from 1984 to 1997. This yielded data on 20 prey species, hunted at 76 differnt times and places. Eleven of the 20 prey species were targeted on three or more occasions, which was deemed sufficient data for further analysis.

The four sites where data on Chimpanzee predation were obtained. Bugir et al. (2021).

The most favoured prey of the Chimpanzees at three of the four study sites was the Ashy Red Colobus Monkey, Piliocolobus tephrosceles. Infant and juvenile Bushbuck, Tragelaphus scriptus, and Western Guereza Colobus Monkey, Colobus guereza occidentalis, were all taken preferentially when available. However, Bugir et al. do note that their study was based upon a series of snapshots, and could have missed important changes in prey preference. 

The Chimpanzees also appeared to avoid certain potential prey species, notably Olive Baboon, Papio anubis, Blue Duiker, Philantomba monticola, Gentle Monkey, Cercopithecus mitis, and Red-tailed Monkey, Cercopithecus ascanius. This appears to indicate that Chimpanzees have an upper size preference for prey at about 7.6 kg, with species larger than this being avoided, and those slightly below it being preferred. This indicates that an adult male Chimpanzee will take prey up to 18% of its own size.

Chimpanzee prey preferences determined by mean Jacobs’ index values ±1 SE calculated from 13 studies at four sites. Significantly preferred prey, taken in excess of their abundance, are delineated by black bars. Gray bars denote significantly avoided prey which are less likely to be pursued irrespective of their abundance. Blue bars are prey that are taken or avoided according to their availability. Bugir et al. (2021).

There is also an apparent relationship between the sex ratio within a group, and the likelihood that the Chimpanzees will develop a preference for certain types of prey. This appears to be a far greater contributing factor than group size, prey body weight, or hunting method.

Having preferred prey species and avoiding potential prey which is to large to be taken safely is a trait that Chimpanzees share with other predators; in the case of Chimpanzees the upper size limit for prey appears to be about 7.6 kg. Larger prey, such as Baboons or Ungulates, are generally avoided, although immature members of these species may be hunted. This is a much lower threshold than that of Humans living in hunter-gatherer societies, who will typically take prey up to a limit of 276% of the size of an adult female. Meat plays an important role in the diet of both species, but is clearly much more important to Humans, with up to 60% of the diet of Humans living in hunter-gatherer societies coming from Animals, including about 35% from Mammals, while the Chimpanzee diet is typically about 4% meat. This suggests that the preference for meat may have been a major driver in the brain-size increase seen in Humans compared to Chimpanzees, and that Chimpanzees cannot be seen as apex predators in the way that Humans, Lions, and Tigers are.

The largest driver of variation in prey choice appears to be the sex ration within groups of Chimpanzees, with groups with a high proportion of males taking a much wider range of prey. In all Chimpanzee groups males are the primary hunters, but females sometimes join hunting expeditions, and make use of tools when they do so.

The main purpose in hunting among Chimpanzees appears to be social, whereas in Human hunter-gatherers meat is a substantial part of the diet, and thus Humans appear to fit the optimal foraging model better than Chimpanzees, with Humans efficiently hunting a wide range of prey, with masses ranging from 2.5 kg to 535 kg, using techniques that are safe to themselves and which yield high energy returns. However, Humans may be being driven to target a wider range of prey by their own success, with many Human hunters living in 'empty forests' in which the majority of potential prey species have either been wiped out, or are present at only very low densities. 

Despite the differences in hunting emphasis, the 'empty forests' phenomenon may not be exclusive to Humans, with the Chimpanzees of the Kibale National Park in having apparently become so efficient at hunting Red Colobus Monkeys that that species is in danger of being wiped out in the area, which presumably would in turn result in the Chimpanzees being forced to switch to alternative prey.

Understanding the hunting preferences of Chimpanzees has the potential to improve our ability to conserve both the Chimpanzees themselves and their prey species. Knowing what is being hunted by Chimpanzees, and which groups of Chimpanzees are doing the hunting, gives us the ability to bolster prey-species populations, thereby improving the survival chances of the Chimpanzees themselves. This understanding also has the potential to give some insight into the behaviour of early Hominids, and thereby improve our understanding of our own ancestors. 

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.