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135-461: Although it is well established that there was a massive loss of biodiversity in the Late Devonian, the timespan of this event is uncertain, with estimates ranging from 500,000 to 25 million years, extending from the mid-Givetian to the end-Famennian. Some consider the extinction to be as many as seven distinct events, spread over about 25 million years, with notable extinctions at the ends of

270-650: A Carboniferous stromatoporoid. Fossils of the Ordovician labechiid Lophiostroma have been reported from sediments as young as the Triassic , but this is another case of poor preservation and uncertain identity. Finally, the calcitic sponge Kyklopora , from the Serpukhovian stage (upper Mississippian ) of Russia, has tentatively been identified as a clathrodictyid. Labechiid-like fossils are abundant in early Pennsylvanian ( Bashkirian ) reef deposits of

405-439: A mutualistic (mutually beneficial) relationship with endosymbiotic microbes. Modern scleractinian corals are mixotrophs , deriving energy from both tiny prey items and zooxanthellae , photosynthetic algae which live within their cells. Zooxanthellae additionally assist the corals’ biochemical processes, allowing for expeditious growth rates. No equivalent organisms are known in modern sponges, though some demosponges do host

540-492: A 2020 United Nations Environment Programme report found that most of these efforts had failed to meet their goals. For example, of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only six were "partially achieved" by 2020. This ongoing global extinction is also called the holocene extinction or sixth mass extinction. The current rate of global biodiversity loss

675-549: A decrease in biodiversity and species numbers . Habitat destruction is in fact the leading cause of biodiversity loss and species extinction worldwide. For example, habitat loss is one of the causes in the decline of insect populations (see the section below on insects ). The direct effects of urban growth on habitat loss are well understood: building construction often results in habitat destruction and fragmentation. This leads to selection for species that are adapted to urban environments. Small habitat patches cannot support

810-520: A deep loss of ecosystem diversity. On a smaller scale, 57% of genera and at least 75% of species did not survive into the Carboniferous. These latter estimates need to be treated with a degree of caution, as the estimates of species loss depend on surveys of Devonian marine taxa that are perhaps not well enough known to assess their true rate of losses, so it is difficult to estimate the effects of differential preservation and sampling biases during

945-524: A few detractors. Up until the 1990s, some Soviet and Eastern Bloc specialists continued to regard stromatoporoids as cnidarians or cyanobacterial accumulations akin to stromatolites or thrombolites . The first unambiguous stromatoporoids appeared in the Ordovician, but superficially similar organisms have been reported from the Early Cambrian . These are most likely cases of convergent evolution rather than true forerunners. One example were

1080-411: A few species making up the majority of an assemblage by volume. The most diverse stromatoporoid assemblages were biostromes on carbonate platforms at intermediate depths, away from muddier basins or saltier shallows. The predominant species were usually laminar or low domical in form. High domical species and other complex forms only developed in calmer settings, where there is little risk of toppling. In

1215-479: A global cooling event. This oxygen isotope excursion is known from time-equivalent strata in South China and in the western Palaeotethys , suggesting it was a globally synchronous climatic change. The concomitance of the drop in global temperatures and the swift decline of metazoan reefs indicates the blameworthiness of global cooling in precipitating the extinction event. The "greening" of the continents during

1350-499: A global oceanic anoxic event that intruded into epicontinental seas. A positive δO excursion is observed across the Frasnian-Famennian boundary in brachiopods from North America , Germany, Spain , Morocco , Siberia, and China ; conodont apatite δO excursions also occurred at this time. A similar positive δO excursion in phosphates is known from the boundary, corresponding to a removal of atmospheric carbon dioxide and

1485-487: A high volume of cyanobacteria within their skeletons. Several lines of evidence suggest a mixotrophic lifestyle for stromatoporoids, though none are unambiguous. Their ratios of oxygen and carbon isotopes overlap with corals to an extent. If one assumes that latilaminae (growth interruptions parallel to laminae) are annual (like tree rings), stromatoporoid growth rates can reach 2 to 10 mm per year, equivalent to corals and much higher than modern calcareous sponges. On

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1620-635: A hugely significant phase of evolution known as the Silurian-Devonian Terrestrial Revolution . Their maximum height went from 30 cm at the start of the Devonian, to 30 m archaeopterids, at the end of the period. This increase in height was made possible by the evolution of advanced vascular systems, which permitted the growth of complex branching and rooting systems, facilitating their ability to colonise drier areas previously off limits to them. In conjunction with this,

1755-410: A large role in biodiversity loss. More than half of the worlds biodiversity is hosted in tropical rainforest. Regions that are subjected to exponential loss of biodiversity are referred to as biodiversity hotspots . Since 1988 the hotspots increased from 10 to 34. Of the total 34 hotspots currently present, 16 of them are in tropical regions (as of 2006). Researchers have noted in 2006 that only 2.3% of

1890-669: A role in conjunction with the Viluy Traps. Bolide impacts can be dramatic triggers of mass extinctions. An asteroid impact was proposed as the prime cause of this faunal turnover. The impact that created the Siljan Ring either was just before the Kellwasser event or coincided with it. Most impact craters, such as the Kellwasser-aged Alamo , cannot generally be dated with sufficient precision to link them to

2025-800: A role. Freshwater ecosystems such as swamps, deltas, and rivers make up 1% of earth's surface. They are important because they are home to approximately one third of vertebrate species. Freshwater species are beginning to decline at twice the rate of species that live on land or in the ocean. This rapid loss has already placed 27% of 29,500 species dependent on fresh water on the IUCN Red List . Global populations of freshwater fish are collapsing due to water pollution and overfishing . Migratory fish populations have declined by 76% since 1970, and large "megafish" populations have fallen by 94% with 16 species declared extinct in 2020. Marine biodiversity encompasses any living organism that resides in

2160-547: A shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns , lepidosigillarioid lycopsids , and aneurophyte and archaeopterid progymnosperms . Fish were also undergoing a huge radiation, and tetrapodomorphs, such as the Frasnian-age Tiktaalik , were beginning to evolve leg-like structures. The Kellwasser event and most other Later Devonian pulses primarily affected

2295-408: A single impact as entirely inconsistent with available evidence, although a multiple impact scenario may still be viable. Near-Earth supernovae have been speculated as possible drivers of mass extinctions due to their ability to cause ozone depletion . A recent explanation suggests that a nearby supernova explosion was the cause for the specific Hangenberg event , which marks the boundary between

2430-642: A stable environment, stromatoporoids could grow to very large sizes exceeding several meters in width or height. The largest singular stromatoporoid fossil ever reported is a 30-meter (98 feet) wide Actinostroma expansum from the Frasnian-age Shell Rock Formation of Iowa . Despite their preference for soft flat sediment, stromatoporoids occasionally contributed to built-up skeletal mounds ( bioherms ) with successive waves of burial and recolonization or regrowth. Shelf -margin stromatoporoid bioherms are particularly well-developed in

2565-517: A supernova origin. However, there is currently no direct evidence for this hypothesis. Other mechanisms put forward to explain the extinctions include tectonic -driven climate change , sea-level change, and oceanic overturning. These have all been discounted because they are unable to explain the duration, selectivity, and periodicity of the extinctions. Loss of biodiversity Biodiversity loss happens when plant or animal species disappear completely from Earth ( extinction ) or when there

2700-752: A taller, narrower form to survive high sedimentation rates, while acquiring a flatter and more stable form to survive in energetic shallow waters. Some stromatoporoids appear to grow intermittently in a ‘ragged’ style even without sediment burial, as indicated by an abundance of encrusters under the overhanging 'shelves'. Stromatoporoid growth forms include: From Stearn et al. (1999) and The Treatise on Invertebrate Paleontology : Like many fossil invertebrates, stromatoporoids have long been regarded as an enigmatic group with an uncertain relationship to modern taxa. For much of their history of study, stromatoporoid fossils could only be observed externally or through natural cross-sections. Several hypotheses developed in

2835-418: A thinly encrusting layered skeleton, augmented by internal rods, external knobs, and radiating nutrient canals. These features were equated with pillars, mamelons, and astrorhizae, respectively. In 1970, several living sponges were found to possess a calcareous skeletal framework very similar to Hydractinia and stromatoporoids. The modern sponges, collectively termed sclerosponges , immediately reinvigorated

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2970-578: A variety of depths, light levels, and fluctuating sea level regimes. In these regards, they were more similar to corals than to modern calcareous sponges, which generally occupy a narrow selection of rocky habitats with high nutrient supply and low light levels. Unlike corals, stromatoporoids usually settled on soft substrates, so their ‘reefs’ occupied only a single level rather than a multi-tiered vertical framework of built-up skeletons. Flat, horizontally-extensive ‘reefs’ are formally known as biostromes . Stromatoporoid reefs had fairly low diversity, with only

3105-531: A ‘ missing link ’ between the ancestral labechiids and their presumed descendants, the actinostromatids. Labechiid diversity contracted during the Late Ordovician mass extinction and throughout the Silurian, while clathrodictyids and actinostromatids diversified substantially. The other four stromatoporoid orders (Amphiporida, Stromatoporellida, Stromatoporida, and Syringostromatida) also originated in

3240-469: Is a decrease or disappearance of species in a specific area. Biodiversity loss means that there is a reduction in biological diversity in a given area. The decrease can be temporary or permanent. It is temporary if the damage that led to the loss is reversible in time, for example through ecological restoration . If this is not possible, then the decrease is permanent. The cause of most of the biodiversity loss is, generally speaking, human activities that push

3375-580: Is a major driver of biodiversity loss, with infrastructure present in roughly 80% of KBAs. Infrastructure development leads to conversion and fragmentation of natural habitat, pollution and disturbance. There can also be direct harm to animals through collisions with vehicles and structures. This can have impacts beyond the infrastructure site. Humans are changing the uses of land in various ways, and each can lead to habitat destruction and biodiversity loss. The 2019 Global Assessment Report on Biodiversity and Ecosystem Services found that industrial agriculture

3510-680: Is an extinct clade of sea sponges common in the fossil record from the Middle Ordovician to the Late Devonian . They can be characterized by their densely layered calcite skeletons lacking spicules . Stromatoporoids were among the most abundant and important reef-builders of their time, living close together in flat biostromes or elevated bioherms on soft tropical carbonate platforms . Externally, some species have raised bumps (mamelons) and star-shaped crevices (astrorhizae), which together help vent exhalant water away from

3645-428: Is another threat to global biodiversity . For example, coral reefs —which are biodiversity hotspots —will be lost by the year 2100 if global warming continues at the current rate. Still, it is the general habitat destruction (often for expansion of agriculture), not climate change, that is currently the bigger driver of biodiversity loss. Invasive species and other disturbances have become more common in forests in

3780-558: Is believed to be seven times lower than its prehistoric values, while the biomass of marine mammals had declined fivefold. At the same time, the biomass of humans is "an order of magnitude higher than that of all wild mammals", and the biomass of livestock mammals like pigs and cattle is even larger than that. Even as wild mammals had declined, the growth in the numbers of humans and livestock had increased total mammal biomass fourfold. Only 4% of that increased number are wild mammals, while livestock and humans amount to 60% and 36%. Alongside

3915-658: Is common in marine ecosystems, affecting at least 55 marine species. One study found that as seismic noises and naval sonar increases in marine ecosystems, cetacean diversity decreases (including whales and dolphins). Multiple studies have found that fewer fishes, such as cod , haddock , rockfish , herring , sand seal, and blue whiting , have been spotted in areas with seismic noises, with catch rates declining by 40–80%. Noise pollution has also altered avian communities and diversity. Noise can reduce reproductive success, minimize nesting areas, increase stress response, and reduce species abundance. Noise pollution can alter

4050-507: Is due to hunting and trapping for the exotic pet trade. Deforestation , caused by unsustainable logging and agriculture, could be the next extinction driver, because birds lose their habitat and their food. While plants are essential for human survival, they have not received the same attention as the conservation of animals. It is estimated that a third of all land plant species are at risk of extinction and 94% have yet to be evaluated in terms of their conservation status. Plants existing at

4185-654: Is estimated to be 100 to 1000 times higher than the (naturally occurring) background extinction rate , faster than at any other time in human history, and is expected to grow in the upcoming years. The fast-growing extinction trends of various animal groups like mammals, birds, reptiles, amphibians, and fish have led scientists to declare a current biodiversity crisis in both land and ocean ecosystems. In 2006, many more species were formally classified as rare or endangered or threatened ; moreover, scientists have estimated that millions more species are at risk that have not been formally recognized. Deforestation also plays

Late Devonian extinction - Misplaced Pages Continue

4320-550: Is evidence this shift in reef composition began prior to the Frasnian-Famennian boundary. The collapse of the reef system was so stark that it would take until the Mesozoic for reefs to recover their Middle Devonian extent. Mesozoic and modern reefs are based on scleractinian ("stony") corals, which would not evolve until the Triassic period. Devonian reef-builders are entirely extinct in the modern day: Stromatoporoids died out in

4455-464: Is likely that if a supernova did occur, multiple others also did within a few million years of it. Thus, supernovae have also been speculated to have been responsible for the Kellwasser event, as well as the entire sequence of environmental crises covering several millions of years towards the end of the Devonian period. Detecting either of the long-lived, extra-terrestrial radioisotopes Sm or Pu in one or more end-Devonian extinction strata would confirm

4590-620: Is now the Scottish Highlands and Scandinavia , while the Appalachians rose over America. The biota was also very different. Plants, which had been on land in forms similar to mosses and liverworts since the Ordovician , had just developed roots, seeds, and water transport systems that allowed them to survive away from places that were constantly wet—and so grew huge forests on the highlands. Several clades had developed

4725-580: Is often a matter of debate. An October 2020 analysis by Swiss Re found that one-fifth of all countries are at risk of ecosystem collapse as the result of anthropogenic habitat destruction and increased wildlife loss. If these losses are not reversed, a total ecosystem collapse could ensue. In 2022, the World Wildlife Fund reported an average population decline of 68% between 1970 and 2016 for 4,400 animal species worldwide, encompassing nearly 21,000 monitored populations. Insects are

4860-499: Is placed on marine ecosystems near coastal areas because of the human settlements in those areas. Overexploitation has resulted in the extinction of over 25 marine species. This includes seabirds , marine mammals , algae , and fish . Examples of extinct marine species include Steller's sea cow ( Hydrodamalis gigas ) and the Caribbean monk seal ( Monachus tropicalis ). Not all extinctions are because of humans. For example, in

4995-485: Is the main driver of mass species extinction in oceans. Overfishing has reduced fish and marine mammal biomass by 60% since the 1800s. It is currently pushing over one-third of sharks and rays toward extinction. Many commercial fishes have been overharvested: a 2020 FAO report classified as overfished 34% of the fish stocks of the world's marine fisheries. By 2020, global fish populations had declined 38% since 1970. Stromatoporoid Stromatoporoidea

5130-725: Is the primary driver of biodiversity collapse. The UN's Global Biodiversity Outlook 2014 estimated that 70% of the projected loss of terrestrial biodiversity is caused by agriculture use. According to a 2005 publication, "Cultivated systems [...] cover 24% of Earth's surface". The publication defined cultivated areas as "areas in which at least 30% of the landscape is in croplands, shifting cultivation, confined livestock production, or freshwater aquaculture in any particular year". More than 17,000 species are at risk of losing habitat by 2050 as agriculture continues to expand to meet future food needs (as of 2020). A global shift toward largely plant-based diets would free up land to allow for

5265-644: Is the relative representation of a species in a particular ecosystem . It is usually measured as the number of individuals found per sample . The ratio of abundance of one species to one or multiple other species living in an ecosystem is called relative species abundance . Both indicators are relevant for computing biodiversity . There are many different biodiversity indexes . These investigate different scales and time spans. Biodiversity has various scales and subcategories (e.g. phylogenetic diversity , species diversity , genetic diversity , nucleotide diversity ). The question of net loss in confined regions

5400-585: Is trying to take action and promote the restoration and maintenance of the many diverse species of earthworms. Since the 1980s, decreases in amphibian populations, including population decline and localized mass extinctions , have been observed in locations all over the world. This type of biodiversity loss is known as one of the most critical threats to global biodiversity . The possible causes include habitat destruction and modification, diseases, exploitation, pollution , pesticide use, introduced species , and ultraviolet-B radiation (UV-B). However, many of

5535-622: Is usually the most important region for the purpose of species differentiation. In all species, the most conspicuous internal features are laminae , layers arranged transversely (parallel to the living surface of the sponge). Laminae have an intermediate width and spacing (on average around four per millimeter) relative to other layers with the same orientation. Significantly thinner layers, when present, are termed microlaminae , while thickened irregular plates are termed pachystromes . Another universal type of internal structure are pillars , cylindrical rods oriented longitudinally (i.e., perpendicular to

Late Devonian extinction - Misplaced Pages Continue

5670-546: The Akiyoshi Limestone Group in Japan, representing a Panthalassan seamount . Over 60 valid genera of small hypermineralized Mesozoic sponges have been described as stromatoporoids based on their anatomical similarity to stromatoporids, actinostromatids, clathrodictyids, or syringostromatids. One hypothesis suggests a direct line of descent between Paleozoic and Mesozoic forms. Under this interpretation,

5805-784: The Chazy Group of eastern North America and the Machiakou Formation of North China . Labechiids were by far the most diverse stromatoporoids of the Ordovician, and some paleontologists have even ventured to reconstruct lines of descent in this preliminary stage of stromatoporoid evolution. The next order to appear were the Clathrodictyida, in the early Katian stage of the Late Ordovician. It has been suggested that clathrodictyids are descended from labechiids, as part of an evolutionary lineage starting at

5940-489: The Givetian , Frasnian , and Famennian ages. By the Late Devonian, the land had been colonized by plants and insects . In the oceans, massive reefs were built by corals and stromatoporoids . Euramerica and Gondwana were beginning to converge into what would become Pangaea . The extinction seems to have only affected marine life . Hard-hit groups include brachiopods , trilobites , and reef-building organisms ;

6075-500: The Kazachstanicyathida , an order of archaeocyath sponges with low growth habits and porous internal domes comparable to cyst plates. In addition, some colonial coralomorphs or algae ( Maldeotaina , Yaworipora , and the ‘ khasaktiids ’) acquired mesh-like encrusting skeletons with a set of internal rods and domes similar to those of early stromatoporoids. A more probable set of stromatoporoid ancestors evolved in

6210-607: The Kellwasser event (Late Devonian mass extinction). Diversity loss prior to the Kellwasser event was likely a factor of both falling origination rates and slightly elevated extinction rates. Other groups presented unexpected patterns: the formerly rare amphiporids reached their highest diversity in the Frasnian, while labechiids staged a remarkable comeback in the Famennian stage, acquiring levels of diversity not seen since

6345-411: The acronym HIPPO for the main causes of biodiversity loss: H abitat destruction, I nvasive species, P ollution, human over- P opulation and O ver-harvesting . Habitat destruction (also termed habitat loss and habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved to elsewhere or are dead, leading to

6480-418: The depositional environment of sedimentary strata. They hosted a diverse fauna of encrusting symbionts both within and outside their skeletons. Some studies have argued that stromatoporoids were mixotrophs (engaged in a mutualistic relationship with photosynthetic algae), similar to modern scleractinian corals. Though this hypothesis is plausible, circumstantial evidence is inconclusive. Prior to

6615-442: The effects of climate change . An additional cause that may be specific to insects is light pollution (research in that area is ongoing). Scientists have studied loss of earthworms from several long-term agronomic trials. They found that relative biomass losses of minus 50–100% (with a mean of minus 83 %) match or exceed those reported for other faunal groups. Thus it is clear that earthworms are similarly depleted in

6750-525: The planetary boundaries too far. These activities include habitat destruction (for example deforestation ) and land use intensification (for example monoculture farming). Further problem areas are air and water pollution (including nutrient pollution ), over-exploitation , invasive species and climate change . Many scientists, along with the Global Assessment Report on Biodiversity and Ecosystem Services , say that

6885-588: The protected areas with rich biodiversity were in areas containing unexploited fossil fuel reserves worth between $ 3 and $ 15 trillion. The protected areas may be under threat in future. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term applies to natural resources such as water aquifers , grazing pastures and forests , wild medicinal plants , fish stocks and other wildlife . A 2019 Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services report found that overfishing

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7020-440: The substrate . Most were ambitopic (occupying soft substrate such as mud or sand for most of their life), though some were encrusting (concreted onto hard substrates such as rocks or other organisms). The base was stabilized by a crust-like layer covered with concentric wrinkles. The basal layer has historically been termed an epitheca or peritheca, names used for a similar attachment layer in sessile cnidarians. In many species,

7155-646: The 1930s, the eelgrass limpet ( Lottia alveus ) became extinct in the Atlantic once the Zostera marina seagrass population declined upon exposure to a disease. The Lottia alveus were greatly impacted because the Zostera marina were their sole habitats. The main causes of current biodiversity loss are: Jared Diamond describes an "Evil Quartet" of habitat destruction , overkill , introduced species and secondary extinctions . Edward O. Wilson suggested

7290-419: The 1970s, stromatoporoids were most frequently equated with colonial hydrozoans in the phylum Cnidaria (which also includes corals, sea anemones , and jellyfish ). They are now classified as sponges in the phylum Porifera, based on their similarity to modern sclerosponges . True Paleozoic stromatoporoids ( sensu stricto ) encompass seven orders . Two or three of these orders appeared in the Ordovician while

7425-422: The 19th and 20th centuries based on this limited set of data. A few authors suggested that stromatoporoids were sponges or relatives of Gypsina (an encrusting foraminifera ). However, for much of their history the mainstream interpretation was that stromotoporoids were colonial cnidarians , most closely related to mineralized hydrozoans such as Hydractinia and Millepora . Hydractinia in particular has

7560-413: The 20th century. Many car drivers know this anecdotal evidence through the windscreen phenomenon , for example. Causes for the decline in insect population are similar to those driving other biodiversity loss. They include habitat destruction , such as intensive agriculture , the use of pesticides (particularly insecticides ), introduced species , and – to a lesser degree and only for some regions –

7695-684: The 40ka Milankovic cycle . The continued drawdown of organic carbon eventually pulled the Earth out of its greenhouse state during the Famennian into the icehouse that continued throughout the Carboniferous and Permian. Magmatism was suggested as a cause of the Late Devonian extinction in 2002. The end of the Devonian Period had extremely widespread trap magmatism and rifting in the Russian and Siberian platforms, which were situated above

7830-467: The Devonian and Carboniferous periods. This could offer a possible explanation for the dramatic drop in atmospheric ozone during the Hangenberg event that could have permitted massive ultraviolet damage to the genetic material of lifeforms, triggering a mass extinction. Recent research offers evidence of ultraviolet damage to pollen and spores over many thousands of years during this event as observed in

7965-480: The Devonian extinctions merely prompted stromatoporoids to abandon mineralization until the Jurassic, explaining their lack of fossils between the two time intervals. Most paleontologists disagree with this idea, since Paleozoic and Mesozoic ‘stromatoporoids’ differ in several key aspects. In contrast to true Paleozoic stromatoporoids, Mesozoic species have recognizable spicules and a more complex microstructure within

8100-463: The Devonian. Extinction rates appear to have been higher than the background rate for an extended interval covering the last 20–25 million years of the Devonian. During this time, about eight to ten distinct events can be seen, of which two, the Kellwasser and the Hangenberg events, stand out as particularly severe. The Kellwasser event was preceded by a longer period of prolonged biodiversity loss . The Kellwasser event, named for its type locality ,

8235-618: The Devonian. Notable examples can be found in the Canning Basin of Australia , the Miette Complex of Alberta , the Eifel Region of Germany , and southern Belgium . Raised bioherms would have been strengthened by microbial carbonate and other reef-building organisms living between the sponges. As hard sessile objects, stromatoporoids were used as a substrate for ectosymbionts , organisms which attach or encrust onto

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8370-646: The Frasnian / Famennian extinction, with the Kola and Timan-Pechora magmatic provinces being suggested to be related to the Hangenberg event at the Devonian-Carboniferous boundary. Viluy magmatism may have injected enough CO 2 and SO 2 into the atmosphere to have generated a destabilised greenhouse and ecosystem , causing rapid global cooling, sea-level falls, and marine anoxia to occur during Kellwasser black shale deposition. Viluy Traps activity may have also enabled euxinia by fertilising

8505-520: The Frasnian and were nearly wiped out by the extinctions. The extinction event was accompanied by widespread oceanic anoxia ; that is, a lack of oxygen, prohibiting decay and allowing the preservation of organic matter. This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil, especially in Canada and the United States . During

8640-572: The Frasnian-Famennian boundary, leading other studies to reject volcanism as an explanation for the crisis. Another overlooked contributor to the Kellwasser mass extinction could be the now extinct Cerberean Caldera which was active in the Late Devonian period and thought to have undergone a supereruption approximately 374 million years ago. Remains of this caldera can be found in the modern day state of Victoria, Australia. Eovariscan volcanic activity in present-day Europe may have also played

8775-560: The Givetian-Frasnian boundary and in ones coeval with the Hangenberg event. Because coronene enrichment is only known in association with large igneous province emissions and extraterrestrial impacts and the fact that there is no confirmed evidence of the latter occurring in association with the Kellwasser event, this enrichment strongly suggests a causal relationship between volcanism and the Kellwasser extinction event. However, not all sites show evidence of mercury enrichment across

8910-402: The Kellwasser event, but still experienced some diversity loss. Around half of placoderm families died out, primarily species-poor bottom-feeding groups. More diverse placoderm families survived the event only to succumb in the Hangenberg event at the end of the Devonian. Most lingering agnathan (jawless fish) groups, such as osteostracans , galeaspids , and heterostracans , also went extinct by

9045-469: The Kellwasser extinction, though their fossils are rare until the mid-to-late Famennian. The late Devonian crash in biodiversity was more drastic than the familiar extinction event that closed the Cretaceous . A recent survey (McGhee 1996) estimates that 22% of all the ' families ' of marine animals (largely invertebrates ) were eliminated. The family is a great unit, and to lose so many signifies

9180-653: The Kellwassertal in Lower Saxony , Germany , is the term given to the extinction pulse that occurred near the Frasnian–Famennian boundary (372.2 ± 1.6 Ma). Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, which was the first event to be detected based on marine invertebrate record and was the most severe of the extinction crises of the Late Devonian. There may in fact have been two closely spaced events here, as shown by

9315-628: The Late Devonian, the continents were arranged differently from today, with a supercontinent, Gondwana , covering much of the Southern Hemisphere. The continent of Siberia occupied the Northern Hemisphere, while an equatorial continent, Laurussia (formed by the collision of Baltica and Laurentia ), was drifting towards Gondwana, closing the Rheic Ocean . The Caledonian mountains were also growing across what

9450-647: The North American Devonian Seaway. Elevated molybdenum concentrations further support widespread euxinic waters. The timing, magnitude, and causes of Kellwasser anoxia remain poorly understood. Anoxia was not omnipresent across the globe; in some regions, such as South China , the Frasnian-Famennian boundary instead shows evidence of increased oxygenation of the seafloor. Trace metal proxies in black shales from New York state point to anoxic conditions only occurring intermittently, being interrupted by oxic intervals, further indicating that anoxia

9585-653: The Ordovician. This would not last, as stromatoporoids appear to have been completely extinguished during the Hangenberg event (end-Devonian mass extinction) at the end of the Famennian. Putative post-Devonian stromatoporoid fossils have been reported, though their referral to the group is rather ambiguous. A supposed labechiid species ( Labechia carbonaria ) is known from the Viséan stage of England . Some sources consider this species to be based on misinterpreted coral fragments, while others certify its legitimacy as

9720-648: The Ordovician. These forerunners or close relatives are grouped in the incertae sedis sponge order Pulchrilaminida . Pulchrilaminids existed from the late Tremadocian stage (near the end of the Early Ordovician) up to the early Darriwilian stage (about mid-way through the Middle Ordovician). They were low-profile hypercalcified sponges which were similar to stromatoporoids in many respects, with one key difference: pulchrilaminids had spine-like projections (probably homologous with spicules) between

9855-473: The Paleozoic radiation, thus making 'stromatoporoids' (in the broad sense) a polyphyletic group if they are included. Some Carboniferous sponges have been identified as stromatoporoids with a somewhat greater degree of confidence. Stromatoporoids are robust sponges with a dense calcite skeleton lacking spicules . Like other sponges, they grow outwards and upwards from a single base attached firmly to

9990-551: The Siberian species Priscastroma gemini . Though less diverse than their labechiid relatives, Ordovician clathrodictyids were widespread and locally abundant in some areas. The third stromatoporoid order, Actinostromatida, may have originated in the Late Ordovician or the Llandovery Epoch (early Silurian). The precise timing depends on the status of Plumatalinia , a Late Ordovician Estonian genus often considered

10125-588: The Silurian, though they remained fairly subdued compared to the three older groups. Silurian stromatoporoids would face a second round of extinction in the late Silurian ( Pridoli Epoch ), which reduced the number of genera back to Middle Ordovician levels. Stromatoporoids recovered strongly in the Early and Middle Devonian, reaching their overall maximum diversity in the Eifelian stage. Clathrodictyids, stromatoporellids, stromatoporids, and syringostromatids benefited

10260-571: The Silurian-Devonian Terrestrial Revolution that led to them being covered with massive photosynthesizing land plants in the first forests reduced CO 2 levels in the atmosphere. Since CO 2 is a greenhouse gas, reduced levels might have helped produce a chillier climate, in contrast to the warm climate of the Middle Devonian. The biological sequestration of carbon dioxide may have ultimately led to

10395-492: The Wild." Possible solutions can be found in some silvicultural methods of forest management that promote tree biodiversity, such as selective logging, thinning or crop tree management, and clear cutting and coppicing . Without solutions, secondary forests recovery in species richness can take 50 years to recover the same amount as the primary forest, or 20 years to recover 80% of species richness. Human impact on

10530-592: The beginning of the Late Palaeozoic Ice Age during the Famennian, which has been suggested as a cause of the Hangenberg event. The weathering of silicate rocks also draws down CO 2 from the atmosphere, and CO 2 sequestration by mountain building has been suggested as a cause of the decline in greenhouse gases during the Frasnian-Famennian transition. This mountain-building may have also enhanced biological sequestration through an increase in nutrient runoff. The combination of silicate weathering and

10665-650: The burial of organic matter to decreased atmospheric CO 2 concentrations from about 15 to three times present levels. Carbon in the form of plant matter would be produced on prodigious scales, and given the right conditions, could be stored and buried, eventually producing vast coal measures (e.g. in China) which locked the carbon out of the atmosphere and into the lithosphere . This reduction in atmospheric CO 2 would have caused global cooling and resulted in at least one period of late Devonian glaciation (and subsequent sea level fall), probably fluctuating in intensity alongside

10800-421: The calcite-based reef-builders of the great Devonian reef-systems, including the stromatoporoid sponges and the rugose and tabulate corals . It left communities of beloceratids and manticoceratids devastated. Following the Kellwasser event, reefs of the Famennian were primarily dominated by siliceous sponges and calcifying bacteria, producing structures such as oncolites and stromatolites , although there

10935-405: The causes of amphibian declines are still poorly understood, and the topic is currently a subject of ongoing research. Biomass of mammals on Earth as of 2018 The decline of wild mammal populations globally has been an occurrence spanning over the past 50,000 years, at the same time as the populations of humans and livestock have increased. Nowadays, the total biomass of wild mammals on land

11070-403: The cryptic niche. The rim of the hidden areas hosted the greatest diversity of encrusters, most of which were filter feeders reliant on a current to feed. More exposed areas were also encrusted by corals (both tabulate and rugose ), crinoids, bryozoans, and tentaculitids . Like many modern or prehistoric reef-builders, stromatoporoids were host to endosymbionts , organisms living fully within

11205-494: The distribution and abundance of prey species, which can then impact predator populations. Fossil fuel extraction and associated oil and gas pipelines have major impacts on the biodiversity of many biomes due to land conversion, habitat loss and degradation, and pollution. An example is the Western Amazon region. Exploitation of fossil fuels there has had significant impacts on biodiversity. As of 2018, many of

11340-474: The dominant role in extinction. Evidence exists of a rapid increase in the rate of organic carbon burial and for widespread anoxia in oceanic bottom waters. Signs of anoxia in shallow waters have also been described from a variety of localities. Good evidence has been found for high-frequency sea-level changes around the Frasnian–Famennian Kellwasser event, with one sea-level rise associated with

11475-433: The edge of the skeleton, the buried portion ceases growing while the exposed central portion expands outwards to cover the sediment once more. This can create a ‘ragged’ appearance for some fossils, akin to an inverted stack of bowls or plates with sharp lower edges and smoothly curved upper edges. This is one example of how stromatoporoid growth forms can vary somewhat through the animal's lifespan. A single species can acquire

11610-402: The end of the Frasnian. The jawless thelodonts only barely survived, succumbing early in the Famennian. Among freshwater and shallow marine tetrapodomorph fish, the tetrapod-like elpistostegalians (such as Tiktaalik ) disappeared at the Frasnian-Famennian boundary. True tetrapods (defined as four-limbed vertebrates with digits) survived and experienced an evolutionary radiation following

11745-525: The end of the Middle Devonian ( 382.7 ± 1.6 Ma ), into the Late Devonian ( 382.7 ± 1.6 Ma to 358.9 ± 0.4 Ma ), several environmental changes can be detected from the sedimentary record, which directly affected organisms and caused extinction. What caused these changes is somewhat more open to debate. Possible triggers for the Kellwasser event are as follows: During the Late Silurian and Devonian, land plants, assisted by fungi, underwent

11880-646: The end-Devonian Hangenberg event, while rugose and tabulate corals went extinct at the Permian-Triassic extinction . Further taxa to be starkly affected include the brachiopods , trilobites , ammonites , conodonts , acritarch and graptolites . Cystoids disappeared during this event. The surviving taxa show morphological trends through the event. Atrypid and strophomenid brachiopods became rarer, replaced in many niches by productids , whose spiny shells made them more resistant to predation and environmental disturbances. Trilobites evolved smaller eyes in

12015-436: The environment has driven a range of species extinct and is threatening even more today . Multiple organizations such as IUCN and Royal Botanic Gardens, Kew suggest that around 40% of plant species are threatened with extinction. The majority are threatened by habitat loss , but activities such as logging of wild timber trees and collection of medicinal plants, or the introduction of non-native invasive species , also play

12150-403: The event; others dated precisely are not contemporaneous with the extinction. Although some evidence of meteoric impact have been observed in places, including iridium anomalies and microspherules, these were probably caused by other factors. Some lines of evidence suggest that the meteorite impact and its associated geochemical signals postdate the extinction event. Modelling studies have ruled out

12285-481: The evolution of seeds permitted reproduction and dispersal in areas which were not waterlogged, allowing plants to colonise previously inhospitable inland and upland areas. The two factors combined to greatly magnify the role of plants on the global scale. In particular, Archaeopteris forests expanded rapidly during the closing ages of the Devonian. These tall trees required deep rooting systems to acquire water and nutrients, and provide anchorage. These systems broke up

12420-470: The first volcanic phase is in agreement with the age of 372.2 ± 3.2  Ma proposed for the Kellwasser event. However, the second volcanic phase is slightly older than Hangenberg event, which is dated to around 358.9 ± 1.2  Ma. Coronene and mercury enrichment has been found in deposits dating back to the Kellwasser event, with similar enrichments found in deposits coeval with the Frasnes event at

12555-424: The fossil record and that, in turn, points to a possible long-term destruction of the ozone layer. A supernova explosion is an alternative explanation to global temperature rise, that could account for the drop in atmospheric ozone. Because very high mass stars, required to produce a supernova, tend to form in dense star-forming regions of space and have short lifespans lasting only at most tens of millions of years, it

12690-422: The functioning and biodiversity of terrestrial as well as aquatic ecosystems. For example, "air pollution causes or contributes to acidification of lakes, eutrophication of estuaries and coastal waters, and mercury bioaccumulation in aquatic food webs". Noise generated by traffic, ships, vehicles, and aircraft can affect the survivability of wildlife species and can reach undisturbed habitats. Noise pollution

12825-674: The hot mantle plumes and suggested as a cause of the Frasnian / Famennian and end-Devonian extinctions. The Viluy Large igneous province, located in the Vilyuysk region on the Siberian Craton , covers most of the present day north-eastern margin of the Siberian Platform. The triple-junction rift system was formed during the Devonian Period; the Viluy rift is the western remaining branch of the system and two other branches form

12960-461: The hypothesis that stromatoporoids were sponges. Moreover, closer investigations of stromatoporoid fossils were able to determine that an individual mound represents a single animal, rather than a colonial congregation of polyps . Among the strongest evidence for sponge affinities was the degree of similarity between astrorhizae and exhalant canals, which were easier to homologize than the more integrated canal system of Hydractinia . Proponents of

13095-531: The laminae and pillars which make up the skeleton. Mesozoic ‘stromatoporoids’ are a polyphyletic group, with different species referable to the Demospongiae ( demosponges ) and Calcarea ( calcareous sponges ). Sponges in this category are understudied and many proposed genera have proven to be dubious . Like modern corals, stromatoporoids were gregarious filter feeders which congregated into closely packed patches. They were adaptable and could thrive at

13230-584: The laminae of the skeleton. The first stromatoporoids to evolve belonged to the order Labechiida, which rapidly acquired worldwide diversity in the Middle Ordovician. The oldest reported labechiid species is from the Floian stage (the latter part of the Early Ordovician), but abrupt diversification was delayed until the mid-to-late Darriwilian stage, simultaneous with the disappearance of pulchrilaminids. The oldest stromatoporoid ‘reefs’ are known from

13365-522: The laminae). Laminae and pillars are often straight and internally solid, but they can exhibit distinctive textures and distortions in some subgroups. The cubical open spaces among the laminae and pillar meshwork are known as galleries . In life the galleries would have been filled with seawater, while in fossils the spaces are filled by recrystallized calcite. The galleries may be supplemented by very fine curved plates, termed dissepiments . Some species have more complex skeletons with broader pockets beyond

13500-534: The last several decades. These tend to be directly or indirectly connected to climate change and can cause a deterioration of forest ecosystems. Groups that care about the environment have been working for many years to stop the decrease in biodiversity. Nowadays, many global policies include activities to stop biodiversity loss. For example, the UN Convention on Biological Diversity aims to prevent biodiversity loss and to conserve wilderness areas . However,

13635-459: The latter almost completely disappeared. The causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean anoxia , possibly triggered by global cooling or oceanic volcanism. The impact of a comet or another extraterrestrial body has also been suggested, such as the Siljan Ring event in Sweden. Some statistical analysis suggests that the decrease in diversity

13770-479: The level of genetic or taxonomic diversity they formerly could while some more sensitive species may become locally extinct. Species abundance populations are reduced due to the reduced fragmented area of habitat. This causes an increase of species isolation and forces species toward edge habitats and to adapt to foraging elsewhere. Infrastructure development in Key Biodiversity Areas (KBA)

13905-625: The living surface. Internally, stromatoporoids have a mesh-like skeletal system combining extensive horizontal layers (laminae), vertical rods (pillars), and boxy spaces (galleries), along with other features. The most common growth forms range from laminar (flattened) to domical (dome-shaped). Spheroidal, finger-like, or tree-like species also occur, though they are rare in most environments. Stromatoporoids competed and coexisted with other reef-builders such as tabulate and rugose corals . Some stromatoporoid species are useful as environmental proxies, since their form and distribution can help approximate

14040-619: The lowest trophic level require increased conservation to reduce negative impacts at higher trophic levels. In 2022, scientists warned that a third of tree species are threatened with extinction. This will significantly alter the world's ecosystems because their carbon, water and nutrient cycles will be affected. Forest areas are degraded due to common factors such as logging, fire, and firewood harvesting. The GTA (global tree assessment) has determined that "17,510 (29.9%) tree species are considered threatened with extinction. In addition, there are 142 tree species recorded as Extinct or Extinct in

14175-406: The main reason for biodiversity loss is a growing human population because this leads to human overpopulation and excessive consumption . Others disagree, saying that loss of habitat is caused mainly by "the growth of commodities for export" and that population has very little to do with overall consumption. More important are wealth disparities between and within countries. Climate change

14310-434: The mamelons help to channel waste water away from the surface. This mechanism works via Bernoulli's principle , which states that flow pressure increases as speed decreases, such as when the flow is redirected by a vertical barrier. The surface may also be covered with even smaller bumps known as papillae . In contrast to mamelons, papillae are simply external extensions of internal pillars, rather than stacked deflections of

14445-417: The marine community, and had a greater effect on shallow warm-water organisms than on cool-water organisms. The Kellwasser event's effects were also stronger at low latitudes than high ones. Large differences are observed between the biotas before and after the Frasnian-Famennian boundary, demonstrating the extinction event's magnitude. The most hard-hit biological category affected by the Kellwasser event were

14580-407: The modern margin of the Siberian Platform. Volcanic rocks are covered with post Late Devonian–Early Carboniferous sediments. Volcanic rocks, dyke belts , and sills that cover more than 320,000 km, and a gigantic amount of magmatic material (more than 1 million km) formed in the Viluy branch. The Viluy and Pripyat-Dnieper-Donets large igneous provinces were suggested to correlate with

14715-483: The most from this renewal of biodiversity. The arrival of the Late Devonian disrupted this apex of stromatoporoid evolution. Syringostromatids were the first to be affected, virtually disappearing from the fossil record at the start of the Frasnian stage. Actinostromatids, stromatoporellids, and stromatoporids were next in line, with their diversity and reef extent collapsing at the end of the Frasnian in accordance with

14850-424: The most numerous and widespread class in the animal kingdom , accounting for up to 90% of all animal species. In the 2010s, reports emerged about the widespread decline in insect populations across multiple insect orders . The reported severity shocked many observers, even though there had been earlier findings of pollinator decline . There has also been anecdotal reports of greater insect abundance earlier in

14985-411: The narrow galleries. Pachysteles are longitudinal walls which demarcate maze-like corridors, as visible in a transverse cross-section through the skeleton. Stacked dome-shaped pockets, known as cysts, are defined by large convex plates, known as cyst plates . Stromatoporoids can show a variety of growth forms, with low domes or plates as the most common varieties. Whenever an influx of sediment buries

15120-593: The ocean or in estuaries . By 2018, approximately 240,000 marine species had been documented. But many marine species—estimates range between 178,000 and 10 million oceanic species—remain to be described. It is therefore likely that a number of rare species (not seen for decades in the wild) have already disappeared or are on the brink of extinction, unnoticed. Human activities have a strong and detrimental influence on marine biodiversity. The main drivers of marine species extinction are habitat loss, pollution, invasive species , and overexploitation. Greater pressure

15255-451: The oceans with sulphate, increasing rates of microbial sulphate reduction. Recent studies have confirmed a correlation between Viluy traps in the Vilyuysk region on the Siberian Craton and the Kellwasser extinction by Ar/Ar dating. Ages show that the two volcanic phase hypotheses are well supported and the weighted mean ages of each volcanic phase are 376.7 ± 3.4 and 364.4 ± 3.4  Ma, or 373.4 ± 2.1 and 363.2 ± 2.0  Ma, which

15390-477: The onset of anoxic deposits; marine transgressions likely helped spread deoxygenated waters. Evidence exists for the modulation of the intensity of anoxia by Milankovitch cycles as well. Negative δU excursions concomitant with both the Lower and Upper Kellwasser events provide direct evidence for an increase in anoxia. Photic zone euxinia , documented by concurrent negative ∆Hg and positive δHg excursions, occurred in

15525-497: The outer surface of the skeleton. Most encrusting organisms were cryptobionts , meaning that they inhabited shaded spaces and cavities. These hidden areas could be found in gaps between the base of the stromatoporoid and its substrate, or on the underside of shelf-like projections. Displaced or toppled sponges had the potential to host cryptic encrusters on any part of the skeleton. Bryozoans , tabulate corals , crinoids , brachiopods , and clusters of coiled ‘ spirorbids ’ all occupied

15660-422: The oxygen isotope ratio , and thus with the sea water temperature; this may relate to their occupying different trophic levels as nutrient input changed. As with most extinction events, specialist taxa occupying small niches were harder hit than generalists. Marine invertebrates that lived in warmer ecoregions were devastated more compared to those living in colder biomes. Vertebrates were not strongly affected by

15795-532: The pollutants sulfur dioxide and nitrogen oxides . Once sulfur dioxide and nitrogen oxide are introduced into the atmosphere, they can react with cloud droplets ( cloud condensation nuclei ), raindrops, or snowflakes, forming sulfuric acid and nitric acid . With the interaction between water droplets and sulfuric and nitric acids, wet deposition occurs and creates acid rain . A 2009 review studied four air pollutants (sulfur, nitrogen, ozone, and mercury) and several types of ecosystems. Air pollution affects

15930-495: The presence of two distinct anoxic shale layers. There is evidence that the Kellwasser event was a two-pulsed event, with the two extinction pulses being separated by an interval of approximately 800,000 years. The second pulse was more severe than the first. Since the Kellwasser-related extinctions occurred over such a long time, it is difficult to assign a single cause, and indeed to separate cause from effect. From

16065-418: The rest evolved in the Silurian. They rediversified subsequent to mass extinctions at the end of the Ordovician and Silurian, but a more profound decline began in the Late Devonian. With a few putative exceptions, they apparently died out during the Hangenberg event at the end of the Devonian. A number of hypercalcified Mesozoic sponges have been classified as stromatoporoids, but they are likely unrelated to

16200-475: The restoration of ecosystems and biodiversity. In the 2010s over 80% of all global farmland was used to rear animals. As of 2022, 44% of Earth's land area required conservation attention, which may include declaring protected areas and following land-use policies . Air pollution adversely affects biodiversity. Pollutants are emitted into the atmosphere by the burning of fossil fuels and biomass , for example. Industrial and agricultural activity releases

16335-478: The run-up to the Kellwasser event, with eye size increasing again afterwards. This suggests vision was less important around the event, perhaps due to increasing water depth or turbidity. The brims of trilobites (i.e. the rims of their heads) also expanded across this period. The brims are thought to have served a respiratory purpose, and the increasing anoxia of waters led to an increase in their brim area in response. The shape of conodonts' feeding apparatus varied with

16470-507: The simultaneous halving of plant biomass, these striking declines are considered part of the prehistoric phase of the Holocene extinction . Some pesticides , like insecticides , likely play a role in reducing the populations of specific bird species. According to a study funded by BirdLife International , 51 bird species are critically endangered and eight could be classified as extinct or in danger of extinction. Nearly 30% of extinction

16605-409: The skeleton's outer surface. By comparison to modern sponges with a similar anatomy, living tissue was likely only present at the outer surface of the stromatoporoid skeleton. By volume, the majority of the organism was a dead mesh of internal cavities and support structures. Since most stromatoporoid fossils are only visible in vertical or horizontal cross-section, the internal form of the skeleton

16740-456: The skeleton. The most abundant were syringoporids , a type of tube-building tabulate coral. Stromatoporoid fossils with syringoporid burrows are so common that some historical sources have misclassified them as a distinct genus, Caunopora . Syringoporids were able to grow at the same rate as their host in order to prevent being overgrown. Other tabulate corals, rugosan corals, and algal fossils have been found wedged between growth zones within

16875-460: The soil and plant roots that earthworms use to create their biomass. This interferes with carbon and nitrogen cycles . Knowledge of earthworm species diversity is quite limited as not even 50% of them have been described. Sustainable agriculture methods could help prevent earthworm diversity decline, for example reduced tillage. The Secretariat of the Convention on Biological Diversity

17010-536: The soils of fields used for intensive agriculture. Earthworms play an important role in ecosystem function, helping with biological processing in soil, water, and even greenhouse gas balancing. There are five reasons for the decline of earthworm diversity: "(1) soil degradation and habitat loss, (2) climate change, (3) excessive nutrient and other forms of contamination load, (4) over-exploitation and unsustainable management of soil, and (5) invasive species". Factors like tillage practices and intensive land use decimate

17145-413: The sponge hypothesis admitted that sclerosponges and stromatoporoids were not identical in structure; for example, sclerosponges have spicules while true Paleozoic stromatoporoids do not. Several other enigmatic calcareous fossils ( archaeocyathids , disjectoporids , ‘ chaetetids ’) have been reclassified as sponges thanks to this new information. The sponge hypothesis quickly met widespread acceptance, with

17280-553: The stromatoporoid skeleton. Worm borings such as Trypanites are also common endosymbionts, though they apparently only took root in the skeleton after the sponge had died. A persistent question for stromatoporoid ecology is how they were able to compete with corals in shallow, brightly lit areas. One hypothesis is that heavy laminar growth forms were more resistant to damage from waves and storms, yet laminar stromatoporoids were equally common in deep or undisturbed waters. Another hypothesis argues that stromatoporoids benefited from

17415-528: The surface can sink at such a rate that decomposition of dead organisms uses up all available oxygen, creating anoxic conditions and suffocating bottom-dwelling fish. The fossil reefs of the Frasnian were dominated by stromatoporoids and (to a lesser degree) corals—organisms which only thrive in low-nutrient conditions. Therefore, the postulated influx of high levels of nutrients may have caused an extinction. Anoxic conditions correlate better with biotic crises than phases of cooling, suggesting anoxia may have played

17550-642: The upper layers of bedrock and stabilized a deep layer of soil, which would have been of the order of metres thick. In contrast, early Devonian plants bore only rhizoids and rhizomes that could penetrate no more than a few centimeters. The mobilization of a large portion of soil had a huge effect: soil promotes weathering , the chemical breakdown of rocks, releasing ions which are nutrients for plants and algae. The relatively sudden input of nutrients into river water as rooted plants expanded into upland regions may have caused eutrophication and subsequent anoxia. For example, during an algal bloom, organic material formed at

17685-399: The upper surface of the skeleton is ornamented with small mounds known as mamelons . A few species may supplement the mamelons with radiating cracks or grooves known as astrorhizae . Internally, the astrorhizae diverge as independent tapering tubes that intersect smaller open spaces within the skeletal frame. Astrorhizae are generally equated with the exhalant canals of other sponges, while

17820-651: The world is covered with biodiversity loss hotspots, and even though only a small percentage of the world is covered in hotspots, it host a large fraction (50%) of vascular plant species. In 2021, about 28 percent of the 134,400 species assessed using the IUCN Red List criteria are now listed as threatened with extinction —a total of 37,400 species compared to 16,119 threatened species in 2006. A 2022 study that surveyed more than 3,000 experts found that "global biodiversity loss and its impacts may be greater than previously thought", and estimated that roughly 30% of species "have been globally threatened or driven extinct since

17955-491: The year 1500." Research published in 2023 found that, out of 70,000 species, about 48% are facing decreasing populations due to human activities, while only 3% are seeing an increase in populations. Biologists define biodiversity as the "totality of genes , species and ecosystems of a region". To measure biodiversity loss rates for a particular location, scientists record the species richness and its variation over time in that area. In ecology , local abundance

18090-408: Was caused more by a decrease in speciation than by an increase in extinctions. This might have been caused by invasions of cosmopolitan species, rather than by any single event. Placoderms were hit hard by the Kellwasser event and completely died out in the Hangenberg event, but most other jawed vertebrates were less strongly impacted. Agnathans (jawless fish) were in decline long before the end of

18225-471: Was not globally synchronous, a finding also supported by the prevalence of cyanobacterial mats in the Holy Cross Mountains in the time period around the Kellwasser event. Evidence from various European sections reveals that Kellwasser anoxia was relegated to epicontinental seas and developed as a result of upwelling of poorly oxygenated waters within ocean basins into shallow waters rather than

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