Thursday, 29 December 2022

Four children hospitalised by Irukandji Jellyfish stings off K'gari (Fraser) Island, Queensland.

Four children have been airlifted to hospitals in Queensland after being stung by Irukandji Jellyfish at beached on K'gari (Fraser) Island in a two day period. The first incident happened at about 10.30 am on Tuesday 27 December 2022, when a girl described as being of 'primary school age' was stung on the chest while swimming in a creek near Wathumba Beach. She was airlifted to the Hervey Bay Hospital in Pialba, on the mainland, and is described as being in a stable condition. The second incident happened at 2.40 pm the same day, when two girls aged five and seven were stung while swimming at Wathumba Beach. Again, both victims were airlifted to Hervey Bay Hospital, and are in a stable condition. The final incident happened the following day, when a young boy was stung, again in a creek near Wathumba Beach, and flown to Hervey Bay Hospital. 

The Irukandji Jellyfish is a form of Box Jellyfish, Cubozoa, found along the northern coast of Australia, which has both a particularly potent sting and a very small size, making it particularly dangerous to swimmers. The Jellyfish are typically about 5 mm across, though they can reach as much as 30 mm, with tentacles between 5 and 50 mm in length. The sting of these Jellyfish is particularly potent, and can cause muscle aches, back pain, nausea, headaches, chest and abdominal pains, sweating, high blood pressure, difficulty breathing, and in extreme cases death.

An Irukandji Jellyfish, Carukia barnesiABC.

Irukandji Jellyfish are found in the waters to the north of Australia all year round, and move south during the southern summer, making them a threat to bathers along the north Australian coast. The Jellyfish move further south in warmer years, and there are concerns that rising sea temperatures associated with global warming may lead to them moving further south in the future.

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Yprezethinus grimaldii: A Pselaphine Rove Beetle from Early Eocene Cambay Amber.

The Indian Plate separated from Madagascar about 88 million years ago, and collided with Eurasia between 60 and 45 million years ago. Since this time, there has been significant floral and faunal exchange between India and Eurasia, but during the period of isolation, the wildlife of India should, at least in theory, have been closer to that of Madagascar and Africa. However, fossils of African affinities from India during this interval are actually quite rare, while many appear to be more closely related to groups from Europe.

Cambay Amber, from Gujarat State, India, has been dated to about 54.5 million years ago, making it Ypressian (Early Eocene) in age, i.e. dating from the period during which India was colliding with Eurasia. This deposit has yielded a rich assemblage of Insects and other small Arthropods, although the majority of these show Laurasian affinities, and the overall Insect assemblage resembling that of the slightly younger Baltic Amber of northern Europe. Groups with affinities to Eurasian faunas include Electrapine and Melikertine Bees, Lygistorrhinid Flies, and a variety of Termites, while Africa-linked groups include Scelembid Webspinners, and a Paleoamblypygid Whipspider.

In a paper published in the journal Palaeoentomology on 22 September 2022, Joseph Parker of the Division of Biology and Biological Engineering at the California Institute of Technology, and the Division of Invertebrate Zoology at the American Museum of Natural History, describes a new species of Pselaphine Rove Beetle from Cambay Amber, with clear affinities to species from tropical Africa.

The Beetle is assigned to a new species and genus, and given the name Yprezethinus grimaldii, where 'Yprezethinus' derives from 'Ypressian' plus 'Zethinus', a modern genus of Pselaphine Rove Beetle which it resembles, and 'grimaldii' honours the American palaeoentomologist David Grimaldi on the advent of his 65th birthday.

Yprezethinus grimaldii Holotype AMNH Tad-130. (A) Habitus with visible abdominal sternites labelled. (B) Head and pronotum with segments of maxillary palpomeres numbered MP2–MP4. Bythinoplectina-type lateral excavation, eye, apical  pseudosegment of maxillary palp, APs, and mandible, Md, indicated. (C) Right antenna with antennomeres numbered. Note the  club formed from tightly appressed, hemisphere-shaped antennomeres 10 and 11. D, Close-up view of apically globose tubercles  of maxillary palpomeres 3 and 4. (E) Proximal leg articulation, showing conically projecting metacoxa, MC, short metatrochanter, MT, and femur, F. (F) Right metatarsus, F with bythinoplectine-type enlarged third tarsomere spanning distance between arrowheads, and minute first visible tarsomere. Parker (2022).

Yprezethinus grimaldii is about 0.8 mm in length with a flattened body and a glossy black carapace. It is assigned by Parker to the subtribe Bythinoplectina, which is found today in leaf-litter in tropical forests, and considered to be closely related to the modern Zethinus, which is found in the tropical forests of West-Central Africa, from Côte d’Ivoire south to Angola. 

Interestingly, many modern Pselaphine Rove Beetles are considered to be Ant-associated, and while examples of them actually living in Ant's nests are rare, they certainly appear to do better in environments where the leaf-litter community is dominated by Ants. The oldest abundant Ant fossils come from Middle Cretaceous Amber from Kachin State, Myanmar ('Burmese Amber'), but these Ants are quite unlike modern Ants, and no members of any (modern) Ant-associated group are known from Kachin Amber. Cambay Amber represents one of the earliest known ecosystems dominated by this modern Ants, making the discovery of a potentially Ant-related Beetle here significant.

Many of the flying Insects from Cambay Amber appear to be more closely related to Eurasian than African groups. Pselaphine Rove Beetles are, in contrast, poor fliers, as are Webspinners (a group in which, in modern species at least, only the males can fly); Whipspiders are wingless Arachnids and do not fly at all. Thus the flying Insect assemblage at Cambay appears to have been replaced by species from Eurasia, while more terrestrial groups still show African affinities. 

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Interpreting a Late Neolithic/Early Chalcolithic burial from Uğurlu on Gökçeada Island, in the northern Aegean Sea.

The Uğurlu archaeological site is located on the western end of the island of Gökçeada in the northern Aegean Sea. The site is a settlement recording a series of important transitions from the pre-pottery Neolithic through to the Early Bronze Age, covering a period of about 2500 years, from approximately 6800 to 4300 BC, and including the advent of Animal husbandry, agriculture, the use of ceramics, copper, and bronze. 

One of the important features of this site is that it covers the transition from the Neolithic to the Chalcolithic, between about 5500 and 4900 BC, one of the few sites in western Anatolia and the eastern Aegean Islands to do so. As well as seeing the introduction of copper, this interval included reorganisations in the way settlements were laid out and how buildings were constructed, new forms of pottery, and the development of a subsistence economy.

During this period, the settlement at Uğurlu appears to have been divided into two portions; a communal building with a large courtyard to the west, and a group of multi-roomed buildings interpreted as dwellings to the east. A series of pits were excavated to the northwest of this area, partially surrounding the communal building. Most of these pits are between 10 and 90 cm in depth, and are lined with a green clay. These pits contained a variety of materials, including fragments of pottery, Animal bones, clay and marble figurines, bone and flint tools, fragments of shell ornaments (bracelets, rings, etc.), and stone axes. All the pits had been infilled, then covered with large stones.

Four of these pits contained Human remains. Pit 25 contained 7 fragments of Human bone, and pits 29 and 104 contained smaller amounts of material. However, the final pit, 188, is significantly larger, and contains eleven sets of more-or-less complete Human remains.

In a paper published in the journal Documenta Praehistorica on 26 September 2022, Başak Boz of the Department of Archaeology at Trakya University, discusses the way in which these bodies were placed into the pit, and the possible motivations of the people who placed them there.

The location of Uğurlu on the island of Gökçeada in the Aegean. Boz (2022).

Radiocarbon dates were obtained from two bones within the pit, one from the skeleton at the bottom of the pit, interpreted as having been the first skeleton deposited, and one from a Human bone in the uppermost layer of material. The skeleton at the bottom of the pit was dated to 5389-5310 BC, while the upper bone was dated to 5363-5302 BC, making both roughly contemporary with the communal building, the earliest stage of which has been dated to between 5300 and 4300 BC.

The distribution of the pits around the communal building. Boz (2022).

The pit is roughly 1 m in diameter and 2 m deep, making it one of the largest pits from this phase of the occupation. Its floor and walls have been lined with a yellowish green clay plaster. Eleven individual sets of Human remains were placed within the pit, with numerous stones between them; the upper 60-80 cm of the pit comprised an infill of stones above the last body, with a marker stone being placed above this.

The pit also contained a great deal of other material, including two broken grinding stones, a large amount of fragmentary pottery, three pieces of red ochre, some beads, a worked bone, and portions of two Calf skeletons as well as numerous other Animal bone fragments. One large rock within the middle of the pit was covered by a layer of sterile ash roughly 30 cm in diameter and 1.5 cm thick.

The approximate ages and sexes of the skeletons were determined by examination of the pelvis and skull, the pubic symphyses, and tooth wear. The individuals were estimated to be aged from about three years old, to mature adults, aged in their 30s or 40s.

Most of the bones of the individuals in the pit were broken, in some cases severely crushed. However, there is no sign of any of these injuries having been caused before death, and no signs of other pathologies due to ill heath or injury on the skeletons.

Fresh bone breaks (indicated by arrows) related withthe stones between the skeletons. Nejat Yücel in Boz (2022).

The skeleton at the base of the pit (Individual 11) is that of a child aged 5-6 years, laying on top of a layer of apparently randomly distributed stones covering the pit floor. The skeleton is lying on its right side, with the left arm and leg extended towards the south, and the rest of the body in a flexed position. This skeleton was covered by a layer of rocks and Animal bones, including the two broken grinding stones and partial Calf skeletons. One of the grinding stones covered the child's head.

(A) The first individual at the bottom of the pit, (B) stones and Animal bones over the skeleton. Boz (2022).

Above this skeleton another five sets of remains were deposited apparently randomly on top of one-another, with some stones between. All of these skeletons are intact, but their postures imply they were thrown into the pit, rather than being placed carefully. The first of these (Individual 10) is a middle-aged woman, face down with her body in a perpendicular position against the wall of the pit, with the hips and legs about 50 cm higher than the head, and her arms twisted behind her back in a position suggesting they were tied. The two largest stones in the pit were thrown in on top of this woman, with one of them apparently completely crushing her head. The larger of these stones, weighing about 80 kg and in the middle of the pit, was then covered with the layer of sterile ash.

Skeleton of a female (Individual 10) with her hands at her back. Boz (2022).

A further four bodies were then deposited into the pit on top of Individual 10, again in an apparently careless way. These being Individual 9, a child of about twelve years and indeterminate sex, Individual 8, another adult woman in her thirties or forties, Individual 7, and Individual 6, another child of about 10-12 years.

Illustration of the position of individuals in relation to each other. (A) Is the top view of the pit with skeletons and (D)is the lowest level. Only the bodies are shown here to avoid further crowding with the stones in between the bodies. Begona Rodriquez in Boz (2022).

One of these, the mature male, Individual 7, was lying on his back with his legs against the side of the pit. His arms were tightly bent at the shoulders, with his hands on his shoulders, and his legs tightly folded at the knees, suggesting that he also might have been bound before being dumped into the pit.

Illustration of an adult male (Individual 7), the arm and hand positions suggesting binding. Begona Rodriquez in Boz (2022).

Another of these bodies, the male child, Individual 6, was separated into two parts at the waist, with the articulated upper body lying directly on the abdomen of Individual 7, with no stones between them, while the lower part of the body is disarticulated and scattered within the pit.

The next skeleton, Individual 4, is a young adult male (probably in his twenties), apparently laid intentionally on his side, with his legs folded up into his abdomen, and his arms folded against his chest, with his hands on his shoulders. This individual is also thought likely to have been tied in this position, or possibly tightly wrapped in a perishable material, since it is an unnatural position for a body to naturally rest in. 

The tightly flexed position of individual 4. Boz (2022).

Another four individuals above this burial also appeared to have been dumped into the pit, again mixed with a large number of loose rocks, although the limbs of some of these individuals are interwound, suggesting that the infill came after the bodies were deposited. These final skeletons are; Individual 5, a young child, roughly three-to-four years old, Individual 3, an adolescent girl, about eighteen years of age, and Individuals 1 and 2, two more middle aged women, in their thirties or forties. These final burials appear more disturbed than the lower skeletons, with several having portions missing; Individual 1 is missing her right ulna, Individual 3 her right fibula, and Individual 5 the bones of the right lower leg.

Intertwined extremities of different individuals with no fill between them indicating simultaneous disposal of the bodies. Boz (2022).

The burial at Uğurlu is unusual in nature, with eleven individuals jammed into a pit 1 m in diameter and 2 m deep, along with a large quantity of rocks. Fitting this many bodies into such a small hole cannot have been easy, and may have been done over some period of time, giving each body a chance to decay, and thereby take up less space, before the next body was added. This would have required the pit to be covered by some sort of a lid between depositions, with the rocky infill being added at the end of the process. This fits somewhat with the circumstances of the burial, with little material between the bodies, with the exception of the child at the bottom, who appears to have been covered over before the other bodies were added, and is supported by some skeletal elements which appear to have shifted downwards with regards to the bodies from which they originated, notably the pelvis of Individual 7. 

Illustration of the bodies in order in the pit. Begona Rodriquez in Boz (2022).

An alternative possibility is that this was a secondary burial, with the bodies having been stored elsewhere until they were all deposited in the pit together in a single event. This would help to explain the disarticulated nature of the lower half of the child, Individual 6, who could have been in an advanced state of decomposition when deposited. However, the condition of the upper body of the same individual presents a problem for this hypothesis, as even the small bones of the fingers remain articulated, incompatible with such a state of decomposition. Some ancient cultures are known to have practised ritual defleshing or dismemberment between primary and secondary burials, which might explain such a mixed state of articulation, but the absence of cut marks on any bones argues against this. The missing limb portions of the uppermost bodies could also offer evidence for this hypothesis, but the upper part of the pit has also been entered by several Animal burrows, which offer a better explanation for these missing bones, and the fact that only the skeletons at the top of the pit are affected. 

Thus neither of these scenarios quite fits with the available evidence, although it remains likely that the bodies do represent two separate events, the deposition and covering of the first child's body, followed by the later deposition of the remaining ten bodies.

The Late Neolithic-Early Chalcolithic period was one of considerable cultural diversity across the region that encompasses the Balkan Peninsula, Greece, Thrace, the Aegean Islands, and Anatolia, with a wide range of burial customs known. However, the customs of western Anatolia, the region closest to the island of Gökçeada, are poorly represented for this interval.

At the Barcın Höyük VI site in the Marmara region of northwest Anatolia, which was in use between about 6600 and 5900 BC, adult individuals were buried in courtyards, while children were buried in abandoned houses. At Aktopraklık, also in the Marmara region, a Late Neolithic site dated to between 6400 and 6235, all individuals are buried in a flexed position beneath the floors of houses. The first cemeteries appear in the Marmara region in the Chalcolithic at Aktopraklık C and Ilıpınar X/IX.

Further west, infant burials within settlements are known from Ulucak in the seventh millennium BC, but little other information is available.

In the sixth millennium BC, Neolithic burials in the Balkan region also generally occur within settlements, with both flexed and supine burial positions used, although these are generally at different sites. Here, supine burials were the norm in the Mesolithic, but the flexed burials represent a new phenomenon, possibly originating in the Near East. Fragmented burials are also quite known from the Balkans, with parts of bodies having apparently been removed, or even replaced with other objects. Also found in the Balkans are ditch burials, in which individuals were buried away from settlements, and pit burials of both individual and multiple bodies, sometimes after cremation; these pit burials are also known from Greece and Central Europe.

Between about 5400 and 4500 BC distinct cemeteries, outside the bounds of settlements, developed in the Balkans, which has been suggested as evidence of a changing relationship between the dead and the living, although the variety of different ways of dealing with the dead seen before seems to persist in the cemeteries.

Of particular similarity to the Uğurlu sites are the pit cemeteries of the eastern Balkans, particularly Bulgaria, where pits of a variety of shapes were dug outside of settlements, and filled with a mixture of debris, including grinding stones and Animal bones, before being capped off with a stone cairn. Only a minority of these pits have produced Human remains, but those that do often produce multiple sets of remains. These pits have been suggested as a site of sacrifice, in which offerings were placed, and sometimes burned.

No burials from earlier phases at Uğurlu, which may indicate burials taking place away from the settlement as seen elsewhere in the Balkans and Anatolia. The first pits appear at the site during phase IV (roughly 5500-5300 BC), when three pits were dug, which do contain some fragmentary Human material, along with other items. However, the main bout of pit-digging activity occurred during Phase III (5300-4900 BC), during which interval 37 pits were dug, filled with material, and then marked, suggesting they were of some significance to the people of the settlement. Much of the material within the pits is broken and fragmentary, which is in keeping with the tradition of braking and sharing of items, including bodies, which were passed around within communities before burial, during the Neolithic of the Balkans and Near East.

Pit 188 was in use between approximately 5389 and 5310 BC, and appears similar in construction to the other pits at Uğurlu, with the exception that it was significantly larger, and contained multiple sets of Human remains.

It is possible that the sudden deposition of a large number of bodies into a single pit, most of them in a somewhat haphazard way, was a reaction to an epidemic, an event which might provoke the living to dispose of the dead with more haste than was usual within their society. Such an event would be expected to produce dead members of all age groups and both sexes, with a high proportion of children and the elderly. None of the remains from Pit 188 show any sign of disease-associated pathologies, however, pathologies affecting the bones would not be expected with an acute plague-like infection, being more typical of chronic conditions which take their time to kill their victims. However, it is unclear why some of the bodies would have been bound if they were victims of a plague that people wished to dispose of quickly, nor why artefacts would have been placed within the grave with them.

The haphazard nature in which the bodies were placed within the pit, and the fact that some of the victims were bound, raises another possibility, that they were the victims of Human sacrifice, or possibly a local group killed off by invaders. Both warfare and Human sacrifice are known to have been prevalent in the Neolithic and Chalcolithic, with potential massacre sites recorded at Halberstadt (5600-4900 BC) and Talheim (about 5000 BC) in Germany, Asparn-Schlets (about 5000 BC) in Austria, Potočani (about 4200 BC) in Croatia, and Els Traocks (about 5300 BC) in the Spanish Pyrenees. 

Sites associated with warfare tend to have a predominance of young adult and middle aged males, and generally include broken and discarded weapons. The Uğurlu pit contains only one young adult and one middle aged male, along with four middle aged women, one adolescent girl, and four children, an unlikely composition for a war grave. Furthermore, no weapons, broken or otherwise, are present within the pit, nor are there any signs of the sort of injuries expected at a battle site, such as fractures or blunt force traumas. Some fractures are observable, but these appear to have been caused by stones being dropped onto the bodies within the pit, with the stones still being in place at the time of excavation (although it is impossible to tell whether the victims were alive or dead at the time when these injuries were inflicted).

This leaves the possibility of some form of organised Human sacrifice. Human sacrifice can be difficult to identify in the archaeological record, as it is generally impossible to identify why people were killed, but if it is an established part of a culture, then it is likely that people will repeatedly be killed in the same way, probably at regular intervals over an extended period of time. In such cases the victims are typically placed in identical positions, and accompanied by similar grave goods. 

Uğurlu Pit 188 is located in a courtyard along with a series of other pits. It differs from the other pits in size, and the presence of multiple Human skeletons, but otherwise is of similar construction, lined with similar clay, contains similar material (made artefacts, Animal bones), has a similar rocky infill, and is marked with a similar capstone. This does suggest that the pits had some sort of a repeated ritual purpose, but the Human contents of Pit 188 are unusual.

Grave goods can be indicative of ritual sacrifices, but those from Pit 188 are ambivalent. The pit contains portions of two Calves, and two broken grinding stones, as well as several beads, three pieces of red ochre, and a stone covered with ash, but none of these is directly associated with any of the skeletons, and no signs of personal ornamentation are present.

Another possibility, which has been suggested for other sites, is that some of the bodies were sacrificed to accompany a high status individual into the afterlife. The Bergheim Pit in France, dated to about 4000 BC, contains a large number of severed arms, followed by the body of an older male with a severed arm who had apparently died a violent death, then a series of intact skeletons buried in a haphazard way, which has been interpreted as evidence of sacrifices made to accompany the death of an important individual. At Didenheim in the Alsace region of France, burials where individuals placed in specific positions accompanied by individuals in haphazard positions have been interpreted in the same way.

Human sacrifice might be expected to leave distinctive trauma marks on a body, which cannot be observed at Uğurlu. However, there are plenty of ways of killing a Human which do not mark the skeleton (the only remains present at Uğurlu), so this is somewhat inconclusive.

The presence of a carefully placed body, Individual 4, within a large number of haphazardly placed individuals, accompanied by some possible ritual materials (ash, red ochre), may indicate that the other bodies were sacrificial victims placed within the pit to accompany this high-status individual.

Pit 188 at Uğurlu represents the first true burial at this site (some older pits contained fragmentary Human remains), potentially shedding light on the ritual activities and belief system of the people living at the site. However, interpreting this burial site is particularly challenging, given the haphazard way in which the majority of the bodies were deposited, the fact that some (but not all) appear to have been bound before deposition, and one body having been buried in two parts. The context of the pit, surrounded by other pits of apparent ritual importance, makes it likely that this burial had symbolic importance. One possibility is that the majority of those within the pit were killed to accompany an important person, Individual 4, who alone was apparently buried in a pre-planned way. This in turn implies that these people had started to develop a social hierarchy, with some individuals meriting different treatment in death to others. 

Similar accompanying burials are known to have been practised in central and eastern Europe by about 4500 BC, moving westward and southward over the next millennium. If the example at Uğurlu does represent the same phenomenon, then it pushes the origin of this custom back to about 5300 BC, and demonstrates an origin in the Aegean/Anatolian region, where it has not previously been observed.

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Wednesday, 28 December 2022

Magnitude 5.5 Earthquake in southern Eritrea.

The United States Geological Survey recorded a Magnitude 5.5 Earthquake at a depth of 10.0 km, in southern Eritrea, roughly 64 km to the north of the city of Ādīgrat in the Tigray Region of Ethiopia, slightly after 3.20 pm local time (slightly after 12.20 pm GMT) on Monday 26 December 2022. There are no reports of any damage or injuries from this quake, but people may have felt it locally.

The approximate location of the 26 December 2022 Eritrea Earthquake. USGS.

The deserts of Northern Ethiopia and Eritrea are extremely volcanically active, with dozens of volcanoes fed by an emerging divergent margin along the East African Rift; the volcano Erta Ale is on the Ethiopian Rift, the boundary between the Nubian Plate and the Danakil Microplate. The African Plate is slowly splitting apart along the Ethiopian Rift and the East African Rift to the south (which is splitting the Nubian Plate to the West from the Somali Plate to the East). Arabia was a part of Africa till about thirty million years ago, when it was split away by the opening of the Red Sea Rift (part of the same rift system), and in time the Ethiopian and East African Rifts are likely to split Africa into a number of new landmasses. This rifting exerts pressure on the rocks around the margin of the sea, slowly pushing them apart, not smoothly but in fits and starts as the pressure overcomes the tendency of the rocks to stick together, creating shocks that we experience as Earthquakes.

Rifting in East Africa. The Danakil Microplate is the red triangle to the east of the Afar depression at the southern end of the Red Sea. Università degli Studi di Firenze.

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Tuesday, 27 December 2022

Calcitic shells in an Earliest Cambrian Mollusc.

Calcium carbonite can be precipitated from water into two polymorphs with different crystal structures, calcite and aragonite. The type of crystal precipitated by non-biological processes, such as abiotic marine cement and ooid formation, is determined by seawater chemistry, with aragonite being precipitated when magnesium ions are at least twice as numerous in the seawater as calcium ions in the water, and calcite being precipitated when magnesium ions are less numerous. 

Some simple reef-producing organisms also produce calcium carbonate in either form, in response to seawater chemistry, but most organisms produce either calcite or aragonite, with the process occurring within their tissues, where they effectively control the seawater chemistry. Most marine organisms produce low-magnesium calcite rather than aragonite, which is probably advantageous, as calcite is far more stable to changes in seawater chemistry. However, the earliest small shelly fossils from the Lowest Cambrian Terreneuvian Epoch (between 538.8 and 521 million years ago) appear to all have been arogonitic in nature, with various groups of Animals having subsequently evolved calcitic skeletons, which has led to the assumption that the Earliest Cambrian had an 'Aragonitic Ocean', with a high magnessium content.

In a paper published in the journal Geology on 2 November 2022, Luoyang Li of the Frontiers Science Center for Deep Ocean Multispheres and Earth System at the Ocean University of China, and the Laboratory for Marine Mineral Resources at the National Laboratory for Marine Science and TechnologyTimothy Topper of the Shaanxi Key Laboratory of Early Life and Environments at Northwest University, and the Department of Palaeobiology at the Swedish Museum of Natural HistoryMarissa Betts, also of the Shaanxi Key Laboratory of Early Life and Environments at Northwest University, and of the Palaeoscience Research Centre at the University of New England, Dorj Dorjnamjaa of the Institute of Paleontology of the Mongolian Academy of Sciences, Gundsambuu Altanshagai and Gundsambuu Altanshagai, also of the Institute of Paleontology of the Mongolian Academy of Sciences, and of the School of Arts and Sciences at the National University of MongoliaGuoxiang Li of the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology, and Christian Skovsted, again of the Shaanxi Key Laboratory of Early Life and Environments at Northwest University, and the Department of Palaeobiology at the Swedish Museum of Natural History, describe an apparent low-magnesium calcite-producing Mollusc from the Terreneuvian Bayangol Formation at Bayan Gol in the Zavkhan Basin of southwestern Mongolia.

The Bayangol Formation has produced hundreds of shells of the Helcionelloid Mollusc, Postacanthella voronini, considered to be a stem-group Conchiferan (i.e. an early member of the group that includes Bivalves, Gastropods, Cephalopods, Monoplacophorans, and Scaphopods). These come from the Purella shelly biozone, which has been dated to approximately 555 million years ago.

Changes in Metazoan skeletal mineralogy in oscillating seawater conditions across the Ediacaran/Cambrian transition. (A) Animal skeletal mineralogy (top); Mollusc (middle); and constraints on seawater chemistry (bottom). Boxes denote fluid inclusions in marine evaporite deposits; dashed line denotes the possible turning point of seawater chemistry from the Terreneuvian aragonite sea to subsequent calcite sea. E, Ediacaran; Fort, Fortunian. (B) Specimen NRM Mo196849 showing preservation of phosphatic infillings (white arrow), prismatic organic matrix (yellow arrow), and delicate polygonal textures (black arrow) on the surface of the internal molds. (C) Specimen NRM Mo196850 showing overall morphology of Postacanthella voronini. Li et al. (2022).

Seen under the scanning electron microscope, the structure of the shell organic matrix and prismatic crystalline microstructure of the shells of Postacanthella voronini can be seen, replicated in apatite, a phosphatic mineral which has replaced the mineral structure early in the preservation process. Apatite has the ability to adopt the structure of other minerals as it replaces them (most minerals form crystals of a specific shape, tending to destroy fine structures during replacement. This mimicking process gives apatite its name, which derives from the Greek ἀπατάω (apatáō), meaning 'to deceive', but also makes it extremely useful to palaeontologists wishing to study the microstructure of ancient tissues.

The crystalline microstructure of the shell of Postacanthella voronini is comprised of tightly-packed, parallel, columnar prismatic crystals with polygonal cross sections. Clusters of these columnar crystals are bound together by a sinuous intraprismatic organic membrane, similar to that seen in shells of modern Pearl Oysters, Pinctada spp., although the individual crystals of the Postacanthella shells are somewhat smaller than seen in Pinctada. The surface of the Postacanthella shells shows polygonal structures, derived from the cross-sectional shape of the columnar crystals, these being about 10 μm in diameter and slightly convex and cell-like, with the raised margins apparently corresponding to the intraprismatic organic membrane.

Prismatic organic matrix of Terreneuvian Postacanthella and modern Pinctada shells. (A), (B) Digital and scanning electron microscope observations of partly decalcified Pinctada prisms showing three-dimensional organic matrix framework (specimen NRM Mo196851). (C), (D) Scanning electron microscope details of interprismatic and intraprismatic organic matrix of a Cambrian Terreneuvian Postacanthella shell (specimen NRM Mo196852). PM, prismatic organic membrane. Li et al. (2022).

The preservation of prismatic microstructures of Cambrian shells in apatite is not a new concept; it is this preservation which tells us about the aragonite structure of many Cambrian shells (aragonite itself is unstable, and seldom survives for hundreds of millions of years). However, this is the first time that the organic matrix of a Cambrian shell has been observed in this way. This general absence is not surprising, as the organic matrix typically makes up less than 5% of the shell's structure, and is made of proteinaceous material which generally breaks down quickly after the death of the Animal. Fossil shell organic matrices have been recovered before, but only from Mesozoic or later specimens.

However, it is the nature of the crystals moulds preserved within the apatite microstructure that is remarkable. Aragonite and calcite crystals form in quite different ways, with aragonite crystals fanning outwards from a central radiant point, to form a flower-like structure, so that the shell structure comes to resemble a series of interlocking flowers. Calcite crystals, on the other hand, grow in a linear fashion, and bundles of parallel crystals are quite typical. 

Calcitic simple prismatic microstructure of Postacanthella. (A) Scanning electron microscope images of specimen NRM Mo196853 showing overall morphology of Postacanthella voronini. (B), (E), (F) Small prisms with parallel second-order crystal subunits. (C), (H) Inter- and intraprismatic organic membranes of large mature prisms. (D) Prismatic organic matrix. (G) Two adjacent small prisms and mutually parallel second-order structural subunits. (I)–(L) Small individual prisms with numerous lath-like second-order subunits encased within organic sheaths. (M)–(P) Well-defined polygonal texture formed by interprismatic organic membranes. PM, prismatic organic membrane. Li et al. (2022).

The widespread presence of aragonitic shells in Early Cambrian organisms has led to the conclusion that the Earliest Cambrian ocean had a high-magnessium, 'arogonitic' nature. Under such circumstances, it would be easier for organisms to evolve the ability to develop aragonite shells, which would then persist within evolutionary lineages. 

Most organisms will produce either calcite or aragonite shells regardless of the water chemistry (as the crystal formation occurs within their tissues, where chemistry is under their control), with switches between the two systems being rare. This means that organisms will, in theory, develop the ability to form calcium carbonate crystals of a type that matches the water chemistry.

This is not, however, an absolute rule. The Micrabaciids, a group of Sclerectinian Corals today restricted to the deep oceans, produce aragonitic skeletons, but first appeared in the Cretaceous, when the seas had a high calcium, low magnesium chemistry (i.e. a 'calcite' ocean). Some calcite-producing Bivalves will produce aragonite shells if places in water with a high enough magnesium content. Furthermore, there has been a general tendency throughout the Phanerozoic for organisms in warm seas to produce aragonitic shells, while those in cold seas make shells from calcite.

Molluscs are unique in their ability to secrete calcium carbonate crystals from an organic membrane within the shell. In the aragonitic Terreneuvian ocean, Mollusc shells were built from aragonite in a variety of ways, including prismatic aragonite, foliated aragonite, and various regular-irregular fibrous microstructures. Subsequently, in the calcitic seas of the Stage 3 Cambrian and above, Molluscs developed the ability to secrete calcite from their shell membranes, forming foliated calcite and calcitic semi-nacre microstructures. Postacanthella voronini appears to be an exception to this rule, having already developed the ability to secrete a low-magnesium calcite shell in the high-magnessium shell in the high magnesium aragonitic Terreneuvian ocean.

This in turn suggests that the selection of a calcium carbonate polymorph when developing the ability to secrete a shell is influenced by, but not absolutely controlled by seawater chemistry.

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Monday, 26 December 2022

Four skiers injured by avalanche in Austria.

Four skiers have been injured after being hit by an avalanche on Mount Trittkopf, a 2700 m summit near the village of Lech am Arlberg in the Austrian state of Vorarlberg. The incident happened at about 3.00 pm on Christmas Day (25 December) 2022. Ten skiers were initially reported missing following the incident, but all of them have now been located. One of the injured skiers has been airlifted to a hospital in Innsbruck, but none is thought to have sustained life-threatening injuries.

A rescue team on Mount Trittkopf in western Austria on 25 December 2022. Austria Presse Agentur.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

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