Hangenberg event
   HOME

TheInfoList



OR:

The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinction, is a
mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...
that occurred at the end of the Famennian stage, the last stage in the
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
Period (roughly 358.9 ± 0.4 million years ago). It is usually considered the second-largest extinction in the Devonian Period, having occurred approximately 13 million years after the Late Devonian mass extinction (Kellwasser event) at the Frasnian-Famennian boundary. The event is named after the Hangenberg Shale, which is part of a sequence that straddles the Devonian-
Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
boundary in the
Rhenish Massif The Rhenish Massif, Rhine Massif or Rhenish Uplands (, : 'Rhenish Slate Uplands') is a geologic massif in western Germany, eastern Belgium, Luxembourg and northeastern France. It is drained centrally, south to north by the river Rhine and a few ...
of
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
.


Geological evidence

The Hangenberg Event can be recognized by its unique multi-phase sequence of sedimentary layers, representing a relatively short interval of time with extreme fluctuations in the climate, sea level, and diversity of life. The entire event had an estimated duration of 100,000 to several hundred thousand years, occupying the upper third of the 'Strunian' (latest Famennian), and a small portion of the early
Tournaisian The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from Ma to Ma. It is preceded by the Famennian (the uppermost st ...
. It is named after the Hangenberg Black Shale, a distinctive layer of anoxic sediment originally found along the northern edge of the
Rhenish Massif The Rhenish Massif, Rhine Massif or Rhenish Uplands (, : 'Rhenish Slate Uplands') is a geologic massif in western Germany, eastern Belgium, Luxembourg and northeastern France. It is drained centrally, south to north by the river Rhine and a few ...
in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
. This layer and its surrounding geological units define the "classic" Rhenish succession, one of the most well-studied geological examples of the extinction. Sequences equivalent to the Rhenish succession have been found at over 30 other sites on every continent except
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, confirming the global nature of the Hangenberg Event. File:Kowala Quarry Hangenberg succession.jpg, The Hangenberg succession at Kowala Quarry in Poland:
A – cephalopod-rich nodular limestone (equivalent to Wocklum Limestone)
B – marly shale, including the Hangenberg Black Shale (HBS) at its base
C – marly limestone (equivalent to Stockum Limestone)
D – marls and limestones (equivalent to Stockum Limestone and later units)


Prelude and extinction – the lower crisis interval

Below the Hangenberg Event strata is the Wocklum Limestone, a pelagic unit rich in fossils (especially ammonoids). In some places the Wocklum Limestone grades into the Drewer Sandstone, a thin
turbidite A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...
deposit which initiates the lower crisis interval. Increased
erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
and siliciclastic input indicates that the Drewer Sandstone was deposited during a minor marine regression (sea level fall). This may have been caused by a small glacial phase, but other evidence suggests a warm and wet climate at the time. The uppermost part of the Wocklum Limestone and the Drewer Sandstone occupy the LE
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
zone. They also belong to the ''praesulcata''
conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
zone (named after '' Siphonodella/Eosiphonodella praesulcata'') and the DFZ7
foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
zone (characterized by ''Quasiendothyra kobeitusana''). The last pre-extinction ammonoid faunas are dominated by wocklumeriids, forming the ''Wocklumeria'' genozone (also known as the UD VI-D zone). A very short subzone (UD VI-D2) diagnosed by ''Epiwocklumeria'' occurs in the first few layers of the lower crisis interval. The main marine extinction pulse begins abruptly with the subsequent deposition of the Hangenberg Black Shale, a layer of organic material deposited in
anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...
deep-water environments. This is correlated with the beginning of the LN spore zone, indicated by the first occurrence of '' Verrucosisporites nitidus''. However, in some areas the boundary between the LE and LN zones is unclear and possibly based on geography more than chronology. The black shale was deposited during a large
marine transgression A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...
(sea level rise), as indicated by flooding reducing the input of terrestrial spores and increasing
eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
. The Hangenberg Black Shale corresponds to the '' Postclymenia'' zone (UD VI-E), an ammonoid genozone based on massive extinctions within the group, rather than new occurrences. This is also the case for the ''costatus''–''kockeli'' Interregnum (''ck''I) conodont zone. Foraminifera disappear from the fossil record during the black shale interval. Uranium-Lead dating of ash beds in
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...
provide dates of 358.97 ± 0.11 Ma and 358.89 ± 0.20 Ma below and above the black shale. This constrains the main marine extinction pulse to a duration of 50,000 to 190,000 years.


Glaciation – the middle crisis interval

In the middle crisis interval, the black shale grades into a thicker deposit of more oxygenated shallow-water sediment. It may be represented by shale ( Hangenberg Shale) or
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
( Hangenberg Sandstone), and fossils are still rare. These layers are still within the ''ck''I conodont zone and LN spore zone, and foraminifera are still absent. However, ammonoid fossils switch over to the lower ''Acutimitoceras (Stockumites'') genozone (UD VI-F), indicating that post-Devonian ammonoids were beginning to diversify after the main extinction pulse. A major marine regression occurred during the middle crisis interval, as indicated by the increased amount of erosion and river-supplied siliciclastic material. Some areas even show deep incised valley fill deposits, where rivers have cut into their former
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
s. Strata in
Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...
suggest that the sea level fell by more than 100 meters (328 feet) during the middle crisis interval. This regression was caused by a cooling episode, and time-constrained
glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
deposits have been found in
Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...
and
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
(which would have been high-
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
areas), as well as the Appalachian Basin (which would have been a tropical alpine environment). These are known to have been deposited within the LE and/or LN spore zones, which are difficult to distinguish outside of Europe. Less well-constrained glacial deposits have also been found in
Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...
,
Libya Libya, officially the State of Libya, is a country in the Maghreb region of North Africa. It borders the Mediterranean Sea to the north, Egypt to Egypt–Libya border, the east, Sudan to Libya–Sudan border, the southeast, Chad to Chad–L ...
,
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
, and
central Africa Central Africa (French language, French: ''Afrique centrale''; Spanish language, Spanish: ''África central''; Portuguese language, Portuguese: ''África Central'') is a subregion of the African continent comprising various countries accordin ...
. The Late Famennian glacial phase, along with other short glacial phases in the
Tournaisian The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from Ma to Ma. It is preceded by the Famennian (the uppermost st ...
and Visean, acted as a prelude to the far larger and more prolonged Late Paleozoic Ice Age which stretched across much of the Late Carboniferous and Early Permian.


Aftershocks – the upper crisis interval

The upper crisis interval begins with the return of prominent
carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
rocks: a
marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...
y unit, the Stockum Limestone, spans the Devonian–Carboniferous (D–C) boundary. Foraminifera reappear in the fossil record within the Stockum Limestone, forming the DFZ8 zone characterized by '' Tournayellina pseudobeata''. The base of the Stockum Limestone also sees the beginning of the '' Protognathodus kockeli'' conodont zone and further ammonoid diversification within the upper ''Acutimitoceras (Stockumites)'' genozone (LC I-A1). A major extinction among land plants and palynomorphs indicates the beginning of the VI spore zone shortly before the D–C boundary. 'Survivor' faunas of marine invertebrates, such as the last cymaclymeniid ammonoids and phacopid trilobites, also die out at this time, making it the second largest extinction pulse of the Hangenberg Crisis. Conodont zones (usually characterized by ''Protognathodus kuehni'' or ''Siphonodella/Eosiphonodella sulcata'') define the D–C boundary, but difficulty in finding reliable and universal index taxa has complicated study of the boundary in many areas. The sea level fluctuated during the upper crisis interval, as several minor regressions and transgressions continued to occur around the D–C boundary. Nevertheless, the general trend was sea level rise, with the melting of the glaciers which formed in the middle crisis interval. In the early Tournaisian, the crisis finally ends at the base of the Hangenberg Limestone, a fossiliferous limestone superficially similar to the pre-crisis Wocklum Limestone. The base of the Hangenberg Limestone is characterized by the first occurrence of gattendorfiine ammonoids (making up the '' Gattendorfia'' genozone, LC I-A2) and the MFZ1 foraminifera zone.


Extinction severity

Along with the Givetian and Frasnian stages, the Famennian was qualitatively acknowledged as having elevated extinction rates as early as Raup and Sepkoski's 1982 landmark paper on mass extinctions. However, late Famennian extinction rates were typically considered to be of lesser taxonomic severity than those in the Kellwasser Event, one of the "big five" mass extinctions. Depending on the method used, the Hangenberg Event typically falls between the fifth and tenth deadliest post-
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
mass extinctions, in terms of marine genera lost. Most estimates of proportional extinction have low resolution, only as fine as the stages in which the extinctions occur. This can lead to uncertainty in differentiating between the Hangenberg Event and other Famennian extinctions in broad-scale extinction trackers. Benton (1995) estimated that 20–23.7% of all families went extinct in the Famennian, with marine families at a proportion of 1.2–20.4%. About 27.4–28.6% of continental families appear to have died out, but the early and low-diversity nature of Devonian continental life makes this estimate very imprecise. Sepkoski (1996) plotted extinction rates for marine animal
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
and families throughout the
Phanerozoic The Phanerozoic is the current and the latest of the four eon (geology), geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and ...
. This study found that >45% of genera were lost during the Famennian, lowered to ~28% considering only "multiple interval" genera which appeared prior to the stage. The Famennian extinction(s) would be the eighth worst mass extinction by the latter metric. He also found that the percentage loss of "well-preserved" (hard tissue) marine genera in the last substage of the Famennian was around 21%, nearly as large as the rate in the last substage of the Frasnian. The Famennian-wide extinction rate for "multiple interval" marine animal families was around 16%. All of these estimates approached, but did not surpass, the end-Frasnian extinction, and the Givetian extinction(s) also surpassed the Famennian extinction(s) in the "multiple-interval" and "well-preserved" full-stage categories. Using an updated biodiversity database, Bambach (2006) estimated that a total of 31% of marine genera died out in the last substage of the Famennian. By this metric, the Hangenberg Event was the joint seventh-worst post-Cambrian mass extinction, tied with the poorly-studied early Serpukhovian extinction in the Carboniferous. McGhee ''et al''. 2013 attempted to tackle extinction rates via a new resampling protocol designed to counter biases in biodiversity estimates, such as the Signor–Lipps effect and Pull of the Recent. They found a significantly higher extinction rate, with 50% of marine genera lost during the event. This estimate would rank the end-Famennian extinction as the fourth-deadliest mass extinction, ahead of the end-Frasnian extinction. They also ranked the end-Famennian mass extinction as the seventh most ecologically severe extinction, tied with the Hirnantian (end-Ordovician) mass extinction. This was justified by the fact that two whole communities within an ecological megaguild went extinct with no replacements. For the end-Famennian, these were chitinozoans within the
pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...
filter-feeder megaguild, and stromatoporoids within the attached epifaunal (seabed-living) filter-feeder megaguild. Other taxa impacted by the extinction rediversified or their niches were filled rather quickly, but these communities were exceptions. By comparison, the end-Frasnian extinction was ranked as the fourth most ecologically-severe mass extinction, and the Givetian crisis was ranked as the eighth. Even in areas with oxygenated seabeds, such as parts of Morocco, the ecospace of Hangenberg event communities was restricted to only a few ecological groups, particularly slow-moving pelagic predators (i.e. ammonoids and acanthodians) and epifaunal sessile
filter feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...
s (i.e. bivalves and
bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...
ns).


Impact on life


Reef builders

Reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
ecosystems disappeared from the fossil record during the Hangenberg Event, not returning until the late Tournaisian.
Metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ho ...
(
coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
and
sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...
) reefs had already been devastated by the Frasnian–Famennian event, and were still recovering during the Famennian. The end of the Famennian not only eliminated the metazoan reef community, but also many calcimicrobial reefs which were previously unscathed. Nevertheless, in the absence of pressures from metazoan communities, there was a brief resurgence of microbial carbonate in the early Tournaisian, a similar pattern to other mass extinctions. The last true stromatoporoid sponges, a major group of Devonian reef builders, completely died out in the Hangenberg Event. Conversely, tabulate corals were apparently not strongly impacted. Rugose corals, which were already fairly rare, experienced a large extinction and ecological turnover before rediversifying in the Tournaisian.
Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...
ns maintained high rates of both speciation and extinction during the late Famennian, with only a small drop in overall richness. The Hangenberg event effectively "refreshed" bryozoan diversity, eliminating old clades and allowing new forms to radiate and eventually reach a diversity peak in the Visean stage.


Other invertebrates

Ammonoids were nearly wiped out by the Hangenberg Event, a fact noted very early in the study of the extinction. One major Famennian group, the clymeniids, were already suffering smaller extinctions just prior to the event. Although clymeniids survived the extinction event itself, they became a dead clade walking and died out shortly after it. Ammonoid extinction rates were highest near the base of the '' Postclymenia evoluta'' zone, in the early part of the crisis. 75% of remaining families, 86% of genera, and 87% of species died out at this time. A few cymaclymeniids (including ''Postclymenia'') briefly expanded into a cosmopolitan 'survivor' fauna, but ultimately died out at the end of the crisis. Only one ammonoid family, the Prionoceratidae, survived the full extinction interval and went on to rediversify into later goniatite groups. Extinction in non-ammonoid
nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...
s and
gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...
is poorly studied, but appears to have been significant as well. Bivalves were barely affected, even in anoxic deep-water environments. Bivalves in the family Naiaditidae apparently took advantage of the Famennian glaciation to expand from polar regions towards the equator, sparking diversification in the Carboniferous tropics.
Brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...
diversity was somewhat impacted by the event, with survival largely based on ecology. Deep-water rhynchonellids and chonetids completely died out, but extinction among neritic (shallow-water) taxa is less clear-cut. Some neritic taxa expanded after the initial extinction pulse but died out at the end of the crisis with other members of the 'survivor' fauna.
Crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...
s survived relatively unscathed, and instead used the extinction as an opportunity to drastically increase their diversity and body size. The two remaining orders of
trilobite Trilobites (; meaning "three-lobed entities") are extinction, extinct marine arthropods that form the class (biology), class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most succ ...
s, Phacopida and Proetida, were strongly affected. The order Phacopida completely died out during the event. Deep-water phacopids were eradicated at the start of the crisis, while widespread shallow-water phacopids went extinct slightly later, alongside the cymaclymeniid ammonoids. Proetids were also hit hard, but several families in the group survived and rediversified quickly in the Tournaisian.
Ostracod Ostracods, or ostracodes, are a Class (biology), class of the crustacean, Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant taxon, extant) have been identified,Brandão, S.N.; Antoni ...
s experienced notable faunal turnover, with groups such as leperditicopids dying out. At least 50% of pelagic ostracod species went extinct, with some areas having extinction rates up to 66%. Shallow-water species were less affected, with newer taxa replacing older ones late in the crisis.
Plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
suffered severe losses. Acritarchs declined strongly in the late Famennian and were very rare in the Tournaisian.
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
also experienced very high extinction rates which devastated their formerly high diversity. Surviving forms were low in diversity and small in size, an example of the ' Lilliput effect' often seen after mass extinctions. The flask-shaped chitinozoans completely died out during the Hangenberg Event.


Chordates

Conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
s were moderately affected by the event, with different regions varying in the number of species lost. Pelagic conodonts had a total species extinction rate of about 40%, with some areas have a local rate as high as 72%. About 50% of neritic conodont species died out, with survivors characterized by their wide distribution and versatile ecology. Species diversity rebounded soon afterwards, returning close to pre-extinction levels by the middle of the Tournaisian. The Hangenberg Event has also been implicated in the final extinction of several
agnatha Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...
n (jawless fish) groups. Other
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s apparently experienced a major ecological turnover across the Devonian–Carboniferous boundary. The Hangenberg Event's impact on vertebrate evolution approaches "Big Five" events such as the end-Cretaceous and end-Permian extinctions, and far exceeds the impact of the Kellwasser Event. Furthermore, because the vertebrate fossil record of the Famennian is sparse, many extinctions attributed to the Kellwasser event may have actually been caused by the Hangenberg event. Among vertebrates, 44% of high-level clades and over 96% of species were lost during the Hangenberg Event, which occurred globally and did not discriminate between freshwater and marine species.
Placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...
diversity had already decreased in the Kellwasser Event, and all remaining subgroups ( arthrodires, antiarchs, phyllolepids, and ptychodontids) died out abruptly at the end of the Devonian. Sarcopterygians (lobe-finned fish) were also strongly affected: onychodontidans, porolepiforms, tristichopterids, and most other " osteolepidids" went extinct. Some large fish, namely rhizodonts, megalichthyids, and a few acanthodians, survived but failed to significantly increase their ecological disparity, eventually dying out later in the Paleozoic. Dipnoans (lungfish) persisted through the extinction more easily than other sarcopterygians, though they were apparently
extirpated Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions. Local extinctions mark a chan ...
from marine environments. Among the most major ecological changes associated with the extinction are the rise of chondrichthyans (
shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...
s and kin) and actinopterygians (ray-finned fish), which took over in diversity and relative abundance during the Early Carboniferous. These survivors were generally small and fast-breeding, resulting in a decrease in average vertebrate body size across the extinction. Even so, few Devonian chondrichthyan and actinopterygian species survived into the Carboniferous, indicating that these groups also experienced extinctions. Sharks that survived the extinction were greatly reduced in size; only sharks less than a meter long remained, and it would take 40 million years before they started to increase in size again. Four-limbed vertebrates (
stegocephalia Stegocephali (often spelled Stegocephalia, from Greek , lit. "roofed head") is a clade of vertebrate animals containing all fully limbed tetrapodomorphs. It is equivalent to a broad definition of the superclass Tetrapoda: under this broad ...
ns, a.k.a. "
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
s" in the broad sense of the term) evidently survived, eventually leading to the earliest true
amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s, who gave rise to the fully terrestrial (
amniote Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial animal, terrestrial and semiaquatic vertebrates. Amniotes evolution, evolved from amphibious Stem tet ...
)
sauropsid Sauropsida ( Greek for "lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to also include extinct stem-group relatives of modern reptiles and birds (which, as theropod dino ...
s and
synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
s in the Carboniferous. However, no known Famennian "tetrapod" persisted into the Carboniferous, with "
ichthyostegalia Ichthyostegalia is an obsolete order of early amphibians, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade. While the group are recognized as having feet rather than fins, most, if ...
n"- grade stegocephalians such as ''
Ichthyostega ''Ichthyostega'', from Ancient Greek ἰχθύς (''ikthús''), meaning "fish", and στέγη (''stégē''), meaning "roof", is an Extinction, extinct genus of limbed tetrapodomorpha, tetrapodomorphs from the Devonian, Late Devonian of what is ...
'' and '' Acanthostega'' disappearing from the fossil record. A distinct gap in time traditionally separated the Famennian "tetrapod" faunas from their successors in the Early Carboniferous. This fossil hiatus, known as " Romer's Gap", has been linked to the Hangenberg Event. However, recent and continued discovery of many Visean and
Tournaisian The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from Ma to Ma. It is preceded by the Famennian (the uppermost st ...
"tetrapods" has helped to close in this gap, suggesting that the Hangenberg Event affected some vertebrates less severely than previously thought. Coprolitic evidence from early Tournaisian deposits in eastern Greenland has also supported the notion that tetrapods were not as affected by the Hangenberg Event as previously thought.


Plants

During the Famennian, the world was covered by a fairly homogenous and low-diversity land plant flora, dominated by giant '' Archaeopteris'' trees. The palynomorph '' Retispora lepidophyta'' was abundant in most spore zones used to define the terrestrial ecosystems of the Famennian. The major marine extinction pulse of the Hangenberg Event occurred at the boundary between the LE and LN zones, the third- and second-to-last spore zones of the Devonian, respectively. Plants were unaffected at this time. However, they started to decline near the end of the LN zone and the terrestrial ecosystem collapsed at the start of the VI zone, the last spore zone of the Devonian. This land plant extinction, which wiped out most or all of the ''Archaeopteris'' and ''R. lepidophyta'' floras, is correlated with the extinction of 'survivor' faunas in the latter part of the Hangenberg Event. Spore taxa that went extinct include specialized forms with divided spines (likely from an early form of lycopod) as well as widespread tiny spores (''Retispora'', ''Diducites'', ''Rugospora)'' which were probably from fast-growing fern-like plants''.'' Plants were significantly more affected by the Hangenberg event than by the Kellwasser event.


Causes


Anoxia

The Hangenberg event was an
anoxic event An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic ( anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geol ...
marked by a layer of black shale, and has been suggested to have been linked to an increase in terrestrial plant cover. That would have led to increased nutrient supply in rivers and may have led to
eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
of semi-restricted epicontinental seas and could have stimulated
algal bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...
s. However, support for a rapid increase in plant cover at the end of the Famennian is lacking.


Euxinia

Chemical analysis of cores in the Bakken shale suggest that while it was being formed, successive eras of higher sea level corresponded with euxinic (high in toxic hydrogen sulfide and low in oxygen) water in the shallow ocean basin, which could kill animals in the ocean and near the shoreline. As oceans flooded terrestrial basins, water would have entered areas with high nutrient levels, leading to an algal bloom, removing oxygen and then creating hydrogen sulfide as the algae decayed.


Global cooling

Evidence such as glacial deposits in northern Brazil (near the Devonian South Pole) suggests widespread glaciation at the end of the Devonian, as a broad continental mass covered the polar region. The Hangenberg event has been associated with sea-level rise followed swiftly by glaciation-related sea-level fall, and thus a cause of the extinctions may have been an episode of severe global cooling and glaciation at the end of the Famennian, marking the dawn of the Late Palaeozoic Ice Age.


Supernova

One hypothesis for the cause of the last pulse of the extinction notes the abundance of malformed plant spores at the Devonian–Carboniferous boundary. This could implicate increased UV-B radiation and ozone depletion as the kill mechanism, at least for terrestrial organisms. Intense warming may lead to increased convection of
water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...
in the atmosphere, reacting to inorganic chlorine compounds and producing ClO, an ozone-depleting compound. However, this mechanism has been criticized for its slow and weak effect on ozone concentrations, as well as its suspect rejection of volcanic influences. Alternatively,
cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...
s from a nearby
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
would be capable of a similar degree of ozone depletion. The impact of a nearby supernova can be supported or refuted by testing for trace amounts of Plutonium-244 in fossils, but these tests have yet to be published. Ozone depletion could just as easily be explained by an increase in greenhouse gas concentrations resulting from an intense period of arc volcanism. The spore malformations may not even be related to UV radiation in the first place, and could simply be a result of volcanism-related environmental pressures such as
acid rain Acid rain is rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists b ...
.


Volcanism

Evidence of coronene and mercury spikes occurring in the Tien Shan Mountains of southern
Uzbekistan , image_flag = Flag of Uzbekistan.svg , image_coat = Emblem of Uzbekistan.svg , symbol_type = Emblem of Uzbekistan, Emblem , national_anthem = "State Anthem of Uzbekistan, State Anthem of the Republ ...
near the Devonian–Carboniferous boundary has led some researchers to hypothesise a volcanic cause for the Hangenberg event. The activities of the Kola and Timan-Pechora magmatic provinces have been proposed as other hypothetical causes for the Hangenberg event.


Impact event

An asteroid impact has been suggested as a possible cause of the Hangenberg event. However, most impact craters, such as the Hangenberg-aged Woodleigh Crater, cannot be dated precisely enough to determine any causal relationship between the impact and the extinction event.


See also

*
Late Devonian extinction The Late Devonian mass extinction, also known as the Kellwasser event, was a mass extinction event which occurred around 372 million years ago, at the boundary between the Frasnian and Famennian ages of the Late Devonian period.Racki, 2005McGh ...
* Kacak Event * Taghanic event


References

{{DEFAULTSORT:Hangenberg Event Devonian Germany Late Devonian extinctions Shale formations Famennian extinctions