Friday, 5 November 2021

How coal worker’s pneumoconiosis resurfaced in American mines.

Dust associated with mining operations is known to be a major cause of lung disease and other serious health problems. The impact of inhaled dust is cumulative, and can lead to a variety of medical conditions, including coal worker’s pneumoconiosis, silicosis, mixed dust pneumoconiosis, dust-related diffuse fibrosis, and progressive massive fibrosis. In response to this, the US introduced strict laws on the control of dust in coal mines in the 1970s, which resulted in a substantial decline in the number of cases of lung disease among mine workers. However, since the mid 1990s the number of miners with lung disease has risen again steadily, with many cases appearing in younger miners, who have worked their entire working lives in mines working with the new, tighter, regulations on dust control.

This re-appearance of mining-related lung diseases has been particularly prevalent in the Appalachian Region, and is thought to be linked to the practice of targeting thin coal seems, which involves cutting a larger amount of non-coal rock, primarily silica (i.e., quartz) and silicate minerals (cyclosilicates, phyllosilicates, tectosilicates, etc.), which are closely associated with lung disease (the body has no way to remove silica once it gets into the lungs, so that even tiny amounts of these minerals build up over time leading to severe health problems). A variety of other factors have also been suggested as possible caused of or contributers to this re-emergence, including duration and level of exposure, mine operation type, coal and rock-strata geological conditions, dust characteristics (i.e., size, shape, mineralogy, elemental content), dust mitigation techniques, mine size, coal rank, and advancements in cutting technologies. 

The rising number of lung disease case appearing in coal miners has raised concerns with regulators and the scientific community, and in 2014 the Mine Safety and Health Administration brought in a number of new regulations, aimed at reducing exposure limits and improving measurement technology and sampling protocols. However, it is unclear if these measures actually tackle the roots of the problem, and the National Academies of Sciences, Engineering, and Medicine have called for research into a number of factors that are likely to be contributing to the problem.

In a paper published in the International Journal of Coal Science Technology on 13 October 2021, Younes Shekarian and Elham Rahimi of the Department of Mineral Engineering at the New Mexico Institute of Mining and Technology, and the Department of Information Systems at the University of Colorado Denver, Naser Shekarian of the John and Willie Leone Family Department of Energy and Mineral Engineering at Pennsylvania State University, Mohammad Rezaee, also of the Department of Information Systems at the University of Colorado Denver, and Pedram Roghanchi, also of the Department of Mineral Engineering at the New Mexico Institute of Mining and Technology, publish the results of a study which aimed to assess five separate hypotheses about the prevalence of coal worker’s pneumoconiosis in American mines, namely (1) that workers in underground mines are more likely to developing coal worker’s pneumoconiosis than those in other operations, (2) that geographical location is a contributing factor to the prevalence of coal worker’s pneumoconiosis, (3) that size of mine could influence the prevalence of coal worker’s pneumoconiosis among coal miners, (4) that coal rank contributes to the coal worker’s pneumoconiosis incidence rate, and (5) that coal seam thickness could influence the prevalence of coal worker’s pneumoconiosis among coal miners.

Shekarian et al. extracted data from Mine Safety and Health Administration accident/injury and employee/production records. This enabled them to determine the number of cases of coal worker’s pneumoconiosis at each mine, the type of mining caried out there, the number of workers at the mine, the coal production rate, the location of the mine, the coal seem thickness, and the rank of the coal. Each site where at least one instance of coal worker’s pneumoconiosis was recorded was classified as either underground, surface, or other (i.e. augur, milling and preparation plant, office, culm banks, independent shops and yards, surface at underground mine). A total of 21 396 operations were included in the study.

For the purpose of the study, the size of the mines was determined by their number of employees, with mines with less than 50 employees being classified as small, those with between 50 and 100 employees being classified as medium-sized, and those with more than 100 employees being classified as large. Seem width was classified as thin if it was less than 40 inches (101.6 cm) thick, medium if it was between 40 inches and 75 inches (190.5 cm) thick, and thick if it was greater than 75 inches thick. Coal rank was classified as either bituminous or anthracite.

Shekarian et al. found that 93% of the cases of coal worker’s pneumoconiosis recorded in workers at underground mines occurred in the Appalachian Region, with 4% occurring in the Interior Region and 3% in the Western Region. Furthermore, 80% of the mined where cases of coal worker’s pneumoconiosis were recorded were classified as small. At a county level, he highest number of coal worker’s pneumoconiosis cases recorded in underground miners occurred in Boone County, Wet Virginia, where there were 946 reported cases. 

The situation at surface mines followed a similar pattern, with 86% of the cases of coal worker’s pneumoconiosis recorded at surface mines occurring in the Appalachian Region, 9% in the Interior Region, and 5% in the Western Region. This time 86% of the mines where ases of coal worker’s pneumoconiosis were recorded were classified as small. The highest number of coal worker’s pneumoconiosis recorded at surface mines in a single county was in Logan County, West Virginia, where there were 175 recorded cases.

Exposure to respirable coal mine dust varies greatly with the type of mining being carried out. Workers at underground mines are at much greater risk of coal worker’s pneumoconiosis due to the limitations of artificial ventilation systems and the confined spaces in which they are working, which typically means they are exposed to much higher levels of respirable coal mine dust. This was reflected in Shekarian et al.'s study, where 76% of cases of coal worker’s pneumoconiosis reported occurred in underground mineworkers, with 11% of cases reported in workers at surface mines and 13% in workers in other mine operations, mainly mills or preparation plants. Examination of the data chronologically confirmed the drop in the number of cases following the introduction of new tighter regulations in the 1970s, with a sunsequent rise in the number of cases from the 1990s onwards.

 
Number of coal worker’s pneumoconiosis cases as function of (a) mine operation type and (b) year in Unites States during 1986–2018 (total number of cases is 7337). Shekarian et al. (2021).

Geography is known to be a major factor when assessing exposure to respirable coal mine dust, as clusters of mines in different areas are targeting rocks with different geology, that produce different amounts and types of dust. The mines of Central Appalachia, for example, are known to produce more dust sources from non-coal rock strata than mines elsewhere in the US. Correspondingly, previous studies have shown that mineworkers in the eastern region of Appalachian coal field, which includes West Virginia and Pennsylvania, suffer higher rates of coal worker’s pneumoconiosis than miners in other parts of America. 

Shekarian et al. found that, between 1986 and 2018, 106 counties in 16 states reported cases of coal worker’s pneumoconiosis, with the highest number of cases being reported in West Virginia, Kentucky, Virginia, and Pennsylvania. There are thought to be a number of contributing factors behind this, including a higher proportion of silica in respirable coal mine dust, caused by the mines in this region targeting thin coal seems in host rocks with high quarz contents, the smaller size of mining operations here, and a culture of working longer shifts in these mines, resulting in a higher daily exposure to dust.

 
Distribution of coal worker’s pneumoconiosis per state (a) and county (b) for underground, surface, and total data during 1986–2018 in the U.S. Shekarian et al. (2021).

Previous studies have found that mine size is a significant predictor of health issues in mineworkers in the US, with workers at smaller mines having higher rates of coal worker’s pneumoconiosis and abnormal lung functions, and that this is particularly true in Kentucky, Virginia, and West Virginia. It has been suggested that this is because smaller mining operations have fewer resources to invest in health and safety measures, and that concentrations of respirable coal mine dust will tend to be higher in smaller mines.

Shekarian et al. found that most mines in the US, both surface and above ground, are small in size (i.e. have less than 50 employees), but that most miners work at large mines (i.e. mines with more than 100 employees). Simply split by size category, a greater number of cases of coal worker’s pneumoconiosis occurred in miners working at large mines, but that individual miners were more likely to contract coal worker’s pneumoconiosis at smaller mines. 

 
Percentage of underground and surface mines (a) and rate of coal worker’s pneumoconiosis (%) (b) per mine size in the U.S. during 1986–2018. Shekarian et al. (2021).

Coal seam thickness is considered to be another contributing factor for a high instance of coal worker’s pneumoconiosis, and varies from region to region depending on the local geology. The average coal seam thickness in the Central Appalachian Region is lower than in other regions in the US, and mines in this region which target thin coal seams are known to have a high instance of coal worker’s pneumoconiosis.

Shekarian et al. found that only 11% of US mines targeted thick coal seams, with medium seems being the type most often targeted by underground mines (44%) and thin seams the type most often targeted by surface mines (50%). Furthermore, more underground mines targeting medium coal seams reported cases of coal worker’s pneumoconiosis than underground mines targeting either thick or thin seams, while more overground mines targeting thick seams recorded cases than mines targeting medium or thin mines, but in both cases the greatest number of cases were reported at mines targeting thin seams.

 
Rate of coal worker’s pneumoconiosis (%) by seam thickness and mine size in the U.S. underground (a) and surface (b) mines during 1986–2018. Shekarian et al. (2021).

A connection between coal rank (the carbon content of coal, with anthracitic coals having a higher carbon content and therefore yielding more energy than bituminous or sub-bituminous coals) and the occurrence of coal worker’s pneumoconiosis. It has been suggested that the incidence of coal worker’s pneumoconiosis is higher among miners working with bituminous coals than those working with anthracitic coals, even where the levels of respirable coal mine dust remain the same. In the Appalachian Region bituminous coals typically have a high quartz content, which may account for this, although it has been suggested that the surface charge of coal dust particles may be different in mines working anthracitic and bituminous coals.

Examination of the available data by Shekarian et al. revealed that the vast majority (95%) of US coal mines target bituminous coals, with only 9 underground and 59 surface mines targeting anthracites in 2018. Around 95% of cases of coal worker’s pneumoconiosis occurred in mines targeting bituminous coals.

 
Number of underground and surface mines (a), and rate of coal worker’s pneumoconiosis (%) (b), (c) per coal rank in the U.S. during 1986–2018. Shekarian et al. (2021).

The re-appearance of coal worker’s pneumoconiosis among mineworkers in the US in the 1990s caused alarm among many medical workers and scientists studying the field. A number of studies have looked at different factors which might have led to this resurgence, but until Shekarian et al.'s work, no single study had attempted to look at all the possible causes together. Shekarian et al. collated 33 years of mine safety statistics collected by the Mine Safety and Health Administration. Their findings suggest that mine operation, geographic location, mine size, coal seam thickness, and coal rank all contribute to the health risks for underground mineworkers, while at surface mines the picture is less clear, with mine size, geographic location, coal rank, and seam height playing a role, but the correlation between instances and these factors being somewhat more complicated.

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Saturday, 30 October 2021

Estimating the benefits of agroforestry to European wildlife.

The term agroforestry is used to denote practices in which the cultivation of trees is integrated either with the rearing of livestock (in which case it is called silvopasturalism) or other plant crops (silvoarablism). This is a traditional practice across much of Europe, where methods such as grazing livestock in orchards are very widespread, with newer methods being developed more recently, such as short-rotation coppicing being carried out alongside rows of other crops. Systems in which productive trees are grown around the edges of fields are also sometimes considered to be agroforestry, although in these cases the trees are managed separately to the other produce, and may be under separate ownership.

 
Pigs grazing in an open Oak forest system in Spain, a system known as a 'dehesa'. Álvarez (2016).

Europe has suffered particularly severe losses of biodiversity compared to other parts of the world, and this is particularly severe in areas where intensive agriculture is prevalent. Agroforestry promotes a more diverse landscape than arable monoculture, potentially resulting in higher biodiversity. Quantifying the benefits of this could potentially lead to the system being more heavily prioritised under the European Common Agricultural Policy or any successor system.

Agroforestry systems have been well studied in tropical environments, where the evidence suggests that the system offers significant advantages in biodiversity preservation over intensive monocultural systems, but nevertheless tends to lead to reduced biodiversity compared to both primary and secondary forests. The system is less well studied in temperate regions, with most studies tending to concentrate on single groups of Animals, such as Birds or Insects. This leaves the benefits of such systems in Europe somewhat unclear, particularly as the definitions of agroforestry can vary, leading to differences in what systems are included in studies, making comparisons between studies difficult. 

 
Hazel short rotation coppice system alongside crops in Suffolk, UK. Smith et al. (2014).

In a paper published in the journal BMC Ecology and Evolution on 23 October 2021, Anne‑Christine Mupepele of Nature Conservation and Landscape Ecology and Biometry and Environmental System Analysis at the University of Freiburg, and Matteo Keller and Carsten Dormann, also of Environmental System Analysis at the University of Freiburg, present the results of a meta-analysis which combined results from a number of studies of agroforestry systems across Europe.

Mupepele et al. sought to answer three questions, 'What is the effect of agroforestry on biodiversity relative to forests, pastures, cropland or abandoned, shrub-encroached agroforestry?', 'Is the effect of agroforestry on biodiversity influenced by environmental variables, specifically the kind of agroforestry system (silvopasture or silvoarable), sampling method, the specific measure of biodiversity, sampling year, country, climate and the reference used?' and 'How strong and robust is the underlying evidence of these results?'

To which end they located 1411 previous studies of agroforestry systems in Europe, 50 of which were eventually included in the study, representing 69 individual agroforestry sites. Each of these had a direct comparison of a type of agroforestry (silvoarable or silvopastoral) to forests, cropland, pasture, and/or abandoned agroforestry systems.

 
Map of Europe with the number of effect sites per country. Mupepele et al. (2021).

The studies included in the analysis covered sites across Europe where agroforestry systems have been studied between 1984 and 2019. The majority of these sites were caried out in Iberia and the Mediterranean region, with twelve studies from Spain, eight from Portugal, five from Italy, one from France and one from Turkey. Temperate central Europe was represented by six studies from the UK, four from Romania, two each from France, Germany, and Switzerland, and one each from Belgium and northern Italy. The northern boreal region was represented by four studies from Sweden and two from Finland.

Thirty six of the included studies looked at silvopastoral systems, with thirty six studies looking at 52 sites, while silvoarable systems were the subject of thirteen studies looking at seventeen sites. The biodiversity of agroforestry was most commonly compared to that of pasture (23 sites), or forests (21 sites), then abandoned agroforestry systems (thirteen sites) and cropland (12 sites).

 
Sheep grazing in a plantation of Pine and Eucalyptus in Spain. Monica Pelliccia/Mongabay.

The different studies measured biodiversity in different ways, and concentrated on different groups. In order to make a comparison between these diverse studies, Mupepele et al. divided the measured wildlife into five groups, Arthropods, Birds, Bats, Plants, and 'Fungi plus Lichens and Bryophytes', Most of the included studies measured biodiversity at the 'species richness level', although other measures were used.

Mupepelele et al.'s results showed no overall benefit for biodiversity compared to the average derived from all systems. However, silvoarable systems were found to host considerably more biodiversity than other croplands, although they generally hosted less biodiversity than forests. Silvopastoral systems produced less clear results, with measures often producing conflicting results in different studies (i.e. one study might show higher Avian biodiversity in a silvopastoral system than a forest, while another showed the reverse.

Birds and Artropods were typically found at higher levels of diversity in agroforestry envoronments than other systems, Where the original group sorted Arthropods into different groups (e.g. Bees, Beetles and Spiders', then this biodiversity increassed, although this was across all environments, with no change in the beneficial effect of agroforestry.

 
Cereal crops grown alongside trees in Bedfordshire, UK. Agroforestry Research Trust.

Mupepele et al. note that the quality of the studies they were referencing varied somewhat, with some using replicated experimentation with clear controls, whilst others were more observational in nature. To compensate for this, they tried applying a statistical weighting method that gave more value to the more statistically strong studies, but found this made no difference to the overall result. They also carried out funnel plot and Egger’s regression tests for undetected biases in their data, but did not find bias was a problem.

A previous  meta-analysis led by Mario Torralba of the Department of Geosciences and Natural Resource Management at the University of Copenhagen found that agroforestry had a much stronger impact on biodiversity, which caused Mupepele et al. to consider the differences between their findings and that of the earlier study. They note that Torralba et al.'s study was published in 2016, and contained the results from two studies published in 2015 on the benefits of agroforestry in Mediterranean ecosystems, both of which produced very strong positive results, and that if these were excluded from Torrialba et al.'s data then the result was closer to that of Mupepele et al. who included several post 2015 studies with less clear results.

Properly done, meta-analyses can provide a powerful tool for understanding ecological systems in ways not possible from individual studies or unsystematic literature searches. However, the robustness of these results is dependent on the methods used to analyse the data, and in particular the use of weighting to take into account the quality of the studies being referenced. This needs to be done carefully, as failure to apply the right weighting can often lead to very different results. This said, applying weighting to Mupepele et al.'s results resulted in no significant change in the outcome of the study, which strongly supports the robustness of their findings. 

The application of repeated meta-analyses to the same data set can reveal changes over time, as new studies add to the overall picture, dampening the results from atypical studies that might have a profound impact on a smaller data-set. By building a cumulative model in which data were added in chronological order, Mupepele et al. were able to demonstrate that the impact of agroforestry upon biodiversity remained essentially unchanged over time, despite the presence of some anomalous data. They do, however, note that silvoarable systems make up a relatively small proportion of the whole, and that the addition of a higher proportion of studies of these systems in future might change the results of the meta-analysis.

 
Merino Sheep under a Cork Oak in a montado silvopastoral system in Portugal. European Agroforestry Foundation.

The ability to reproduce results is an important principle in science, but can be difficult in fields like ecology, which look at complex natural systems, no two of which are ever completely the same. Mupepele et al.'s results differed strongly from the earlier results of Torralba et al., resulting in their drawing different conclusions; Torralba et al. concluded that agroforestry has a general positive impact upon biodiversity, while Mupepele et al. concluded that this benefit was only clear when agroforestry was compared to croplands, despite both studies having used much of the same data. Mupepele et al. note that Torralba et al. included hedgerows and woody riparian buffers to agricultural land as agroforestry, while Mupepele et al. excluded them on the basis that they are not emplaced for silvicultural purposes (i.e. the trees used in these settings are grown for their value as boundaries, not as a crop in themselves). Neither did Torralba et al. include data from studies which suggested agroforestry had a negative impact on biodiversity. Mupepele et al. believe that scientists should be very clear about what data they are including in meta-analyses, the criteria for choosing this data, and the reasons to do so, in order to help policy-makers judge the significance of different studies. 

Mupepele et al. conclude that silvoarable systems produce an increase in biodiversity compared to conventional croplands, particularly with regard to Birds and Arthropods, but that this increase is not large, and there was no overall positive benefit of agroforestry to all other settings. Notably, silvopasturalism showed no clear benefit over either forestry or conventional pasturelands. Where previous studies have produced enthusiastic support for agroforestry, and strongly suggested these systems are linked to a significant increase in biodiversity, Mupepele take a more cautious approach, noting that relatively few studies find an unqualified link between agroforestry and increased biodiversity, and that literature reviews and meta-analyses need to be careful to include both the positive and negative impacts of systems when drawing on data from multiple studies. Nevertheless, they do conclude that agroforestry can have a positive impact on biodiversity under some circumstances, as well as providing carbon sequestration and other ecosystem services, and that a better understanding of how these systems work could lead to more informed future decisions by policy makers.

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Saturday, 23 October 2021

Vishnuonyx neptuni: A new species of Otter from the late Miocene Hammerschmiede Fauna of Bavaria.

The Hammerschmiede locality in Bavaria, Germany, has been producing Late Miocene Vertebrate and Invertebrate fossils for almost five decades. The fossils are predominantly found within a series of river channels, and date to between 11.62 and 11.44 million years ago. Over 130 species of Vertebrate have been recorded from this location, several of which are unknown from any other location, most notably the Ape, Danuvius guggenmosi. Despite this high diversity, to date only two species of Carnivorans have been described from Hammerschmiede, the Palm Civets Semigenetta sansaniensis and Semigenetta grandis

In a paper published in the Journal of Vertebrate Palaeontology on 16 September 2021, Nikolaos Kargopoulos of the Department of Geosciences at Eberhard Karls University of Tübingen, Alberto Valenciano of the Departamento de Ciencias de la Tierra, and Instituto Universitario de Investigación en Ciencias Ambientales de Aragón at the Universidad de Zaragoza, Panagiotis Kampouridis, also of the Department of Geosciences at Eberhard Karls University of Tübingen, and Thomas Lechner and Madalaine Böhme, also of the Department of Geosciences at Eberhard Karls University of Tübingen, and of the Senckenberg Centre for Human Evolution and Paleoenvironment, describe a new species of 'Bunodont' Otter from the Hammerschmiede locality.

The phylogeny and classification of Otters, Lutrinae, is generally poorly resolved, with the relationship of fossil groups such as the Potamotheriinae and Bunodonts to modern Otters remaining unclear. Bunodont Otters are a (probably paraphyletic) group of large and very large fossil Otters found across Eurasia, Africa, and North America. The classification of this group is itself poorly resolved, with uncertainty about which fossils should be included within it, with one genus, Enhydrictis, having been recently reclassified and no longer thought of as an Otter at all. 

The new species is placed in the genus Vishnuonyx, which contains previously described species from the Miocene of South and Southeast Asia and the Miocene and Pliocene of Africa, and given the specific name neptuni, in reference to Neptune, the Roman god of the seas. The species is described from a right hemimandible, with a first premolar alveolus (canine tooth socket) and the second, third and fourth premolars and first molar intact. A left hemimandible and a number of isolated teeth are also referred to the species. All were recovered from river channel deposits at Hammerschmiede between 2011 and 2020, during excavations carried out by palaeontologists from Eberhard Karls University of Tübingen.

 
The lower dentition of Vishnuonyx neptuni. (A) SNSB-BSPG 2020 XCIV-0301, right hemimandible (holotype; original specimen and screenshots of its 3D model) in labial (A1), (A4), lingual (A2) and occlusal (A3) views; (B) GPIT/MA/16733, left hemimandible in labial (B1), lingual (B2), (B4) and occlusal (B3(, (B5) views; (C) SNSB-BSPG 2020 XCIV-1301 right p4 in labial (C1), lingual (C2) and occlusal (C3) views. Screenshots of the 3D models not in scale. Kargopoulos et al. (2021).

The third premolar of Vishnuonyx neptuni is distinctly asymmetrical, with the bak of the tooth being visibly lager than the front. The main cusp has three crista (ridges) deriving from it, one at the front, one at the back, and one on the inside edge. The inside crysta expands to form part of the wall of the tooth, which hosts one of the three roots of the tooth.

The upper carnassial tooth (front molar, modified to have a cutting edge which occludes the cutting edge on the lower tooth, a diagnostic trait of Carnivorans) has moderate wear on its cutting edge. The tooth has a strong cingulum (convex protuberance below the crown). The tooth has a high paracone (front outer) cusp, which is attached to a ridge a metastyle (ridge on the outer surface). There is no carnassial notch (notch used to hold bone for a crushing bite, a common Carnivoran trait). The protocone, parastyle, and paracone cusps form a line, with the hypocone outside this, behind the paracone. 

 
The upper dentition of Vishnuonyx neptuni. (A) SNSB-BSPG 2020 XCIV-1022, left P3 in occlusal (A1), labial (A2) and lingual (A3) views; (B) GPIT/MA/17347, right P4 (original specimen and screenshots of its 3D model) in occlusal (B1), (B4), labial (B2), (B5) and lingual (B3), (B6) views; (C) SNSB-BSPG 2020 XCIV-1552, left M1 (original specimen and screenshots of its 3D model) in occlusal (C1), (C4), labial (C2), lingual (C3), mesial-occlusal (C5) and mesial (C6) views. Abbreviations: meta, metacone; metal, metaconule; lp, lingual platform; para, paracone; paral, paraconule; prot, protocone; protl, protoconule. Kargopoulos et al. (2021).

The upper molar is complete with some wear to the inner sides of the paracone and metacone. A distinct cingulum is present, although this is less developed towards the forepart of the toorh. The tooth is nearly rectangular in outline, and somewhat slim, although the outer suface is slightly higher at the fore than at the rear. The inner cusps are roughly the same height, and connected by a low crest with a notch towards its middle. Behind these two further cusps, the protoconule and metaconule rear cusps are connected by another ridge.

Neither of the two hemimandibles is complete. The right specimen preserves part of the socket of the canine, part of the angular process (bottom part of the back of the jaw) and part of the masseteric fossa (muscle attachment above the angular process), and everything in between. The muscle attachment is deepest at the top, the hind part of the hemimandible bent inwards, and the angular process small and hook-like. The left mandible is less well preserved, with only part of the canine socket, the cheek teeth and part of the masseteric fossa muscle attachment, however, on this specimen the attachments for the masseter pars superficialis and pars profunda muscles can be seen.

The canine is absent in both hemimandibles. The second premolar is two-rooted and has a distinct cingulum (convex protuberance beneath the crown), particularly on the inner side and towards the rear. The long axis of this tooth is not in line with the long axis of the tooth row. The third and fourth premolars are high and pointed, with their largest cusps towards the middle and inclined backwards. In the third premolar only a single cusp is present, and the tooth has a wrinkled surface. The fourth premolar is taller than the third (and the first molar), and has a second, smaller cusp behind the first. The first molar is broad, with a talonid (crushing region) covering about a third of its surface. The first cusp is wider than this crushing area. This tooth also has wide cingulum. 

The dentition of Vishnuonyx neptuni differs considerably from that of modern Otters, but fits well with the genus Vishnuonyx, which has been confidently assigned to the group based upon more complete material. This genus has previously been described from Asia and Africa, with the Asian specimens being older and less robust than the African specimens; Vishnuonyx neptuni, the first described European member of the genus, appears to be intermediate between these groups in both age and size.

 
Temporospatial distribution of the known species of the genus Vishnuonyx. Kargopoulos et al. (2021).

The oldest known member of the genus, Vishnuonyx maemohensis, comes from Mae Moh in Thailand, and is dated to the Middle Miocene, between 14.2 and 13.2 million years old. Slightly younger is the late Middle Miocene Vishnuonyx chinjiensis from the Siwalik Hills of northwest India, which is thought to be between 13.8 and 12.7 million years old. A second specimen assigned to Vishnuonyx chinjiensis has been described from Ngorora in western Kenya, this specimen being about 12 million years old. Also known from Africa is the Latest Miocene Vishnuonyx? angololensis from Lower Nawata in Lothagam, near the southwestern shores of Lake Turkana, Kenya, which is dated to between 7.3 and 6.6 million years ago. Finally, an Early Pliocene specimen Vishnuonyx sp. has been recorded from Ethiopia and is thought to be between 5.2 and 4.85 million years old. The HAM 4 fossiliferous layer at Hammerschmiede, which produced Vishnuonyx neptuni, has been dated to 11.44 million years ago, making Vishnuonyx neptuni slightly younger than Vishnuonyx chinjiensis.

This suggests that the genus Vishnuonyx originated in Southeast Asia, and migrated westwards through the Indian subcontinent, reaching Europe and East Africa by the end of the Middle Miocene, with the genus persisting in East Africa into the Pliocene. Vishnuonyx neptuni is sufficiently different from other members of the genus to imply a reasonably long period of reproductive isolation, leading Kargopoulos et al. to reason that its ancestors reached Europe before 11.5 million years ago.

Vishnuonyx is thought to have had a semi-aquatic lifestyle similar to that of modern Otters, suggesting that it is most likely to have dispersed from Southeast Asia into South Asia, Europe, and Africa, by water. During the Middle Miocene the Central Paratethys Ocean separated East Africa and Arabia from southern Asia, with the Eastern Paratethys, separated from the Cenral Paratethys by the Araks Straight, forming a connection with Central Europe. This would have provided a plausible route for the westward expansion of the genus Vishnuonyx.

 
The proposed dispersal path of Vishnuonyx from South Asia towards Central Europe and East Africa during the Konkian around 13 million years ago (late Badenian, early Serravalian). Kargopoulos et al. (2021).

The teeth of Otters are adapted for two slightly different diets; catching slippery Fish, and breaking open hard shells. All living Otters pursue both these feeding methods to some extent, although they vary in the extent to which they depend on each method, which is reflected in their dental morphology. In species which primarily feed on hard-shelled prey such as Clams or Crustaceans, the molars tend to be broad and flat with well-developed crushing areas, whereas those that specialise in catching Fish tend to have high pointed cusps useful for catching slippery prey. The teeth of Vishnuonyx neptuni are apparently more adapted towards a piscivorous diet, with high, pointed premolars and a strong cutting blade on the molar. This is at odds with other 'Bunodont' Otters, which appear to have been primarily durophages specialising in hard prey, and suggests an ecology similar to that of the modern Amazonian Giant Otter, Pteronura brasiliensis.

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