Misplaced Pages

#874125

48-506: It followed a series of Cambrian–Ordovician extinction events , and the resulting fauna went on to dominate the Palaeozoic relatively unchanged. Marine diversity increased to levels typical of the Palaeozoic, and morphological disparity was similar to today's. The diversity increase was neither global nor instantaneous; it happened at different times in different places. Consequently, there

96-514: A body of water such as an ocean , lake , or stream , including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word βένθος ( bénthos ), meaning "the depths". Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi ) as well as larger invertebrates , such as crustaceans and polychaetes . Organisms here generally live in close relationship with

144-409: A Cambrian-Ordovician extinction is instead an artifact resulting from a gap in the stratigraphic record. Remains of soft-bodied animals prevalent in earlier, exceptional Cambrian fossil beds were only preserved in later, Ordovician deposits in rare places where special conditions promoted fossilization of soft bodies. Benthic The benthic zone is the ecological region at the lowest level of

192-523: A causal relationship between this volcanism and the biotic turnover. Anoxia and changes in sea level have also been proposed as potential causal factors. The middle Cambrian to early Ordovician is characterized by persistent elevated extinction rates that are thought to have been maintained by anoxic conditions. A decrease in the anoxic conditions of the Cambrian, and an increase in euxinic conditions (or an increase in hydrogen sulfide concentrations) of

240-471: A coupling of seawater oxygenation with Ordovician biodiversity. Another alternative is that the breakup of an asteroid led to the Earth being consistently pummelled by meteorites, although the proposed Ordovician meteor event happened at 467.5±0.28 million years ago. Another effect of a collision between two asteroids, possibly beyond the orbit of Mars, is a reduction in sunlight reaching the Earth's surface due to

288-495: A decrease in benthic macroinvertebrate biomass, which lead to the disappearance of food sources into the substrate. Because the benthic system regulates energy in aquatic ecosystems, studies have been made of the mechanisms of the benthic zone in order to better understand the ecosystem. Benthic diatoms have been used by the European Union's Water Framework Directive (WFD) to establish ecological quality ratios that determined

336-497: A diversification, the event also marked an increase in the complexity of both organisms and food webs . The number of different life modes among hard-bodied organisms doubled. Taxa began to exhibit greater provincialism and have more localized ranges, with different faunas at different parts of the globe. Communities in reefs and deeper water began to take on a character of their own, becoming more clearly distinct from other marine ecosystems. Benthic environments drastically increase in

384-528: A key trigger for GOBE. Furthermore, Ordovician biodiversification pulses were closely linked to terminations of positive carbon isotope excursions, which are characteristic of anoxia, suggesting that diversification occurred in concert with increasing oxygen content. After the Steptoean positive carbon isotope excursion about 500 million years ago, the extinction in the ocean would have opened up new niches for photosynthetic plankton, who would absorb CO 2 from

432-584: A large, nutrient-rich ecospace , favoring diversification. There seems to be an association between orogeny and the evolutionary radiation, with the Taconic orogeny in particular being singled out as a driver of the GOBE by enabling greater erosion of nutrients such as iron and phosphorus and their delivery to the oceans around Laurentia. In addition, the changing geography led to a more diverse landscape, with more different and isolated environments; this no doubt facilitated

480-539: A new habitat. As with the Cambrian Explosion , it is likely that environmental changes drove the diversification of plankton , which permitted an increase in diversity and abundance of plankton-feeding lifeforms, including suspension feeders on the sea floor, and nektonic organisms in the water column . If the Cambrian Explosion is thought of as "producing" the modern phyla , the GOBE can be considered as

528-475: Is a gently sloping benthic region that extends away from the land mass. At the continental shelf edge, usually about 200 metres (660 ft) deep, the gradient greatly increases and is known as the continental slope. The continental slope drops down to the deep sea floor. The deep-sea floor is called the abyssal plain and is usually about 4,000 metres (13,000 ft) deep. The ocean floor is not all flat but has submarine ridges and deep ocean trenches known as

SECTION 10

#1732852195875

576-466: Is not easy to map or observe these organisms and their habitats, and most modern observations are made using remotely operated underwater vehicles (ROVs), and rarely submarines . Benthic macroinvertebrates have many important ecological functions, such as regulating the flow of materials and energy in river ecosystems through their food web linkages. Because of this correlation between flow of energy and nutrients, benthic macroinvertebrates have

624-653: Is real or an artefact of an incomplete fossil record is controversial. Analysis of the Guole Konservat-Lagerstätte and other sites in South China suggests the Furongian Gap did not exist, instead portraying this interval as one of rapid biotic turnovers. Cambrian%E2%80%93Ordovician extinction event The Cambrian–Ordovician extinction event , also known as the Cambrian-Ordovician boundary event ,

672-655: Is recommended in the European Union benthic monitoring program (by Kelly 1998 for the United Kingdom then in the EU and for the EU as a whole by CEN 2003 and CEN 2004) and in some United States programs (by Moulton et al. 2002). Benthic gross primary production (GPP) may be important in maintaining biodiversity hotspots in littoral zones in large lake ecosystems . However, the relative contributions of benthic habitats within specific ecosystems are poorly explored and more research

720-419: Is unlikely to be a simple or straightforward explanation for the event; the interplay of many geological and ecological factors likely produced the diversification. According to a comprehensive study of biodiversity throughout the Palaeozoic, GOBE began 497.05 Ma and ended 467.33 Ma, lasting for 29.72 Myr. GOBE did not constitute one single event, as different clades diversified during different time intervals of

768-607: The Flat Landing Brook Formation in New Brunswick , Canada may have caused rapid climatic cooling and biodiversification. Thallium isotope shifts show an expansion of oxic waters throughout deep water and shallow shelf environments during the latest Cambrian and earliest Ordovician coeval with increasing burrowing depth and complexity observed among ichnofossils and increasing morphological complexity among body fossils. Thus, heightened oxygen availability may have been

816-497: The hadal zone . For comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water column up to the surface. At the other end of the spectrum, benthos of the deep ocean includes the bottom levels of the oceanic abyssal zone . For information on animals that live in the deeper areas of the oceans see aphotic zone . Generally, these include life forms that tolerate cool temperatures and low oxygen levels, but this depends on

864-466: The water column ; even within the benthic zone variations in such factors as light penetration, temperature and salinity give rise to distinct differences, delineated vertically, in the groups of organisms supported. Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column: the pressure difference can be very significant (approximately one atmosphere for each 10 meters of water depth). Many have adapted to live on

912-577: The "filling out" of these phyla with the modern (and many extinct) classes and lower-level taxa. The GOBE is considered to be one of the most potent speciation events of the Phanerozoic era, increasing global diversity severalfold and leading to the establishment of the Palaeozoic evolutionary fauna . Notable taxonomic diversity explosions during this period include that of articulated brachiopods , gastropods , and bivalves . The acritarch record (the majority of acritarchs were probably marine algae) displays

960-577: The Early Ordovician are also believed to be an initiator of the Great Ordovician Biodiversification Event. Trilobites were among the hardest hit organisms by the extinction. Shallow shelf trilobite faunas were hit particularly hard. Trilobites that inhabited the outer edges of shelf environments and slope environments, on the other hand, were minimally impacted by the event. Many trilobites appear to have been adapted to

1008-532: The Floian may reflect the initiation of a cooling through organic carbon burial that has been proposed to have kickstarted GOBE. In the longer term as well, increasing carbon isotope ratios track biodiversity increase, further pointing to a link between cooling and GOBE. The cooling during the Middle and early Late Ordovician in particular is known for its associated burst of biodiversification. The volcanic activity that created

SECTION 20

#1732852195875

1056-610: The Late Cambrian and Early and Middle Ordovician. During the Late Ordovician, diversification slowed down thanks to increased endemism and interbasinal dispersal, bringing an end to GOBE. Possible causes include an increase in marine oxygen content, changes in palaeogeography or tectonic activity , a modified nutrient supply, or global cooling. The dispersed positions of the continents, high level of tectonic/volcanic activity, warm climate, and high CO 2 levels would have created

1104-626: The Ordovician meteor event instead postdating the Darriwilian biodiversity burst by about 600 kyr and the start of glaciation by 800 kyr. Instead of facilitating the radiation, the meteor event may have antagonistically acted to temporarily retard and halt biological diversification according to this thesis. The above triggers would have been amplified by ecological escalation, whereby any new species would co-evolve with others, creating new niches through niche partitioning, trophic layering, or by providing

1152-426: The Ordovician radiation beautifully; both diversity and disparity peaked in the middle Ordovician. The warm waters and high sea level (which had been rising steadily since the early Cambrian) permitted large numbers of phytoplankton to prosper; the accompanying diversification of the phytoplankton may have caused an accompanying radiation of zooplankton and suspension feeders. Taxonomic diversity increased manifold;

1200-517: The ability to influence food resources on fish and other organisms in aquatic ecosystems . For example, the addition of a moderate amount of nutrients to a river over the course of several years resulted in increases in invertebrate richness, abundance, and biomass . These in turn resulted in increased food resources for native species of fish with insignificant alteration of the macroinvertebrate community structure and trophic pathways. The presence of macroinvertebrates such as Amphipoda also affect

1248-484: The amount and variety of bioturbation. The planktonic realm was invaded as never before, with several invertebrate lineages colonising the open waters and initiating new food chains at the end of the Cambrian into the early Ordovician. Among the newcomers colonising the planktonic realm were trilobites and cephalopods. Estuarine environments also experienced increased colonisation by living organisms. And as ecosystems became more diverse, with more species being squeezed into

1296-488: The anoxic conditions of the Cambrian through symbiosis with the sulfur-oxidizing bacteria. Soft-body fossils with morphology characteristic of the Cambrian have been uncovered in Morocco, dated 20 million years post-extinction. The 2010 paper by Roy, Orr, Botting, and their collaborators that announced the discovery suggests that Cambrian species persisted into the mid-Paleozoic. They argue that what had been interpreted as

1344-438: The atmosphere and release large amount of oxygen. More oxygen and a more diversified photosynthetic plankton as the bottom of the food chain, would have affected the diversity of higher marine organisms and their ecosystems. In the Middle to Late Ordovician, after GOBE, an expansion of anoxic waters occurred in sync with a ~50% decline in benthic invertebrates in various epicontinental seas, providing further indirect support for

1392-418: The benthic food chain ; most organisms in the benthic zone are scavengers or detritivores . Some microorganisms use chemosynthesis to produce biomass . Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or a few centimeters into the ocean floor. Those living on the surface of the ocean floor are known as epifauna . Those who live burrowed into

1440-969: The benthic zone. The microbes found in the benthic zone, specifically dinoflagellates and foraminifera , colonize quite rapidly on detritus matter while forming a symbiotic relationship with each other. In the deep sea, which covers 90–95% of the ocean floor, 90% of the total biomass is made up of prokaryotes. To release all the nutrients locked inside these microbes to the environment, viruses are important in making it available to other organisms. Modern seafloor mapping technologies have revealed linkages between seafloor geomorphology and benthic habitats, in which suites of benthic communities are associated with specific geomorphic settings. Examples include cold-water coral communities associated with seamounts and submarine canyons, kelp forests associated with inner shelf rocky reefs and rockfish associated with rocky escarpments on continental slopes. In oceanic environments, benthic habitats can also be zoned by depth. From

1488-439: The deposition of organic matter, and bacterial communities. The amount of material sinking to the ocean floor can average 307,000 aggregates per m per day. This amount will vary on the depth of the benthos, and the degree of benthic-pelagic coupling. The benthos in a shallow region will have more available food than the benthos in the deep sea. Because of their reliance on it, microbes may become spatially dependent on detritus in

Great Ordovician Biodiversification Event - Misplaced Pages Continue

1536-453: The depth of the water. As with oceans, the benthic zone is the floor of the lake, composed of accumulated sunken organic matter . The littoral zone is the zone bordering the shore; light penetrates easily and aquatic plants thrive. The pelagic zone represents the broad mass of water, down as far as the depth to which no light penetrates. Benthos are the organisms that live in the benthic zone, and are different from those elsewhere in

1584-457: The dominance of certain types of algae in Benthic ecosystems as well. In addition, because benthic zones are influenced by the flow of dead organic material , there have been studies conducted on the relationship between stream and river water flows and the resulting effects on the benthic zone. Low flow events show a restriction in nutrient transport from benthic substrates to food webs, and caused

1632-649: The ecological status of lakes in the UK. Beginning research is being made on benthic assemblages to see if they can be used as indicators of healthy aquatic ecosystems. Benthic assemblages in urbanized coastal regions are not functionally equivalent to benthic assemblages in untouched regions. Ecologists are attempting to understand the relationship between heterogeneity and maintaining biodiversity in aquatic ecosystems. Benthic algae has been used as an inherently good subject for studying short term changes and community responses to heterogeneous conditions in streams. Understanding

1680-477: The emergence of bioprovinciality, and speciation by isolation of populations. The widespread reef development on the Baltican shelf in particular is attributable to the landmass's northward drift into more oligotrophic waters, enabling diversification of its reef biota. Widespread volcanism and its delivery of biologically important trace metals has similarly been proposed as a GOBE trigger, albeit controversially. On

1728-551: The entire Early Palaeozoic. An analysis of the Paleobiology Database (PBDB) and Geobiodiversity Database (GBDB) found no statistical basis for separating the two radiations into discrete events. A proposed biodiversity gap known as the Furongian Gap is thought by some researchers to have existed between the Cambrian Explosion and GOBE existed during the Furongian epoch, the final epoch of the Cambrian. However, whether this gap

1776-477: The food web, a more complex tangle of ecological interactions resulted, promoting strategies such as ecological tiering. The global fauna that emerged during the GOBE went on to be remarkably stable until the catastrophic end-Permian extinction and the ensuing Mesozoic Marine Revolution . Recent work has suggested that the Cambrian Explosion and GOBE, rather than being two distinct events, represented one continual evolutionary radiation of marine life occurring over

1824-403: The ocean begins at the shore line ( intertidal or littoral zone ) and extends downward along the surface of the continental shelf out to sea. Thus, the region incorporates a great variety of physical conditions differing in: depth, light penetration and pressure. Depending on the water-body, the benthic zone may include areas that are only a few inches below the surface. The continental shelf

1872-456: The ocean floor are known as infauna . Extremophiles, including piezophiles , which thrive in high pressures, may also live there. An example of benthos organism is Chorismus antarcticus . Sources of food for benthic communities can derive from the water column above these habitats in the form of aggregations of detritus , inorganic matter, and living organisms. These aggregations are commonly referred to as marine snow , and are important for

1920-416: The other hand, global cooling has also been offered as a cause of the radiation, with long-term biodiversity trends showing a positive correlation between cooling and biodiversity during GOBE. An uptick in fossil diversity correlates with the increasing abundance of cool-water carbonates over the course of this time interval. A transient high magnitude shift towards more positive carbon isotope ratios during

1968-471: The potential mechanisms involving benthic periphyton and the effects on heterogeneity within a stream may provide a better understanding of the structure and function of stream ecosystems. Periphyton populations suffer from high natural spatial variability while difficult accessibility simultaneously limits the practicable number of samples that can be taken. Targeting periphyton locations which are known to provide reliable samples – especially hard surfaces –

Great Ordovician Biodiversification Event - Misplaced Pages Continue

2016-664: The shallowest to the deepest are: the epipelagic (less than 200 meters), the mesopelagic (200–1,000 meters), the bathyal (1,000–4,000 meters), the abyssal (4,000–6,000 meters) and the deepest, the hadal (below 6,000 meters). The lower zones are in deep, pressurized areas of the ocean. Human impacts have occurred at all ocean depths, but are most significant on shallow continental shelf and slope habitats. Many benthic organisms have retained their historic evolutionary characteristics. Some organisms are significantly larger than their relatives living in shallower zones, largely because of higher oxygen concentration in deep water. It

2064-671: The subsequent Ordovician period. It eliminated many brachiopods and conodonts , and severely reduced the number of trilobite species. Volcanic activity, particularly that of large igneous provinces, has been speculated to have been the cause of the environmental crisis. The emplacement of the Namaqualand–Garies dykes in South Africa has been dated to 485 mya, the time at which the Cambrian–Ordovician extinction event occurred, although there remains no unambiguous evidence of

2112-442: The substrate (bottom). In their habitats they can be considered as dominant creatures, but they are often a source of prey for Carcharhinidae such as the lemon shark . Because light does not penetrate very deep into ocean-water, the energy source for the benthic ecosystem is often marine snow . Marine snow is organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains

2160-447: The substrate and many are permanently attached to the bottom. The benthic boundary layer , which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral , and bay mud . The benthic region of

2208-506: The total number of marine orders doubled, and families tripled. Marine biodiversity reached levels comparable to those of the present day. Beta diversity was the most important component of biodiversity increase from the Furongian to the Tremadocian . From the Floian onward, alpha diversity dethroned beta diversity as the greater contributor to regional diversity patterns. In addition to

2256-503: The vast dust clouds created. Evidence for this geological event comes from the relative abundance of the isotope helium-3 , found in ocean sediments laid down at the time of the biodiversification event. The most likely cause of the production of high levels of helium-3 is the bombardment of lithium by cosmic rays , something which could only have happened to material which travelled through space. However, rather than sparking evolutionary diversification, other lines of evidence point to

2304-582: Was an extinction event that occurred approximately 485 million years ago ( mya ) in the Paleozoic era of the early Phanerozoic eon . It was preceded by the less-documented (but probably more extensive) End-Botomian mass extinction around 517 million years ago, and the Dresbachian extinction event about 502 million years ago. The Cambrian–Ordovician extinction event ended the Cambrian period , and led into

#874125