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Lundgreni Event
The Lundgreni Event, also known as the Mid-Homerian Biotic Crisis, was an extinction event during the middle Homerian age of the Silurian period. Evidence for the event has been observed in Silurian marine deposits in the Iberian Peninsula, Bohemia, and Poland. Timing In the Kosov quarry in Bohemia, the extinction is observed during the latest ''lundgreni'' biozone and over the course of the ''flemingii'' biozone interval. The following ''parvus'' biozone, corresponding to the ''nassa'', the ''parvus-nassa'', or ''dubious-nassa'' biozones in other localities, represents a post-extinction interval, which is in turn followed by the ''frequens'', ''praedeubeli-deubeli'', and ''ludensis-gerhardi'' biozones that mark the period of recovery from the extinction. Causes Eutrophication and anoxic event, anoxia coeval with abrupt ecological changes have been implicated as extinction mechanisms bringing about the Lundgreni Event. Immediately after the extinction event, geological record ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extinction Event
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 occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity. The "Big Five" mass extinctions In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five particular geological intervals with excessive diversity loss. They were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic, but as more stringent statistical tests have been applied t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Species Richness
Species richness is the number of different species represented in an community (ecology), ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the Abundance (ecology), abundances of the species or their Relative species abundance, relative abundance distributions. Species richness is sometimes considered synonymous with species diversity, but the formal metric species diversity takes into account both species richness and species evenness. Sampling considerations Depending on the purposes of quantifying species richness, the individuals can be Forest inventory#Simple random sampling, selected in different ways. They can be, for example, trees found in an forest inventory, inventory plot, birds observed from a monitoring point, or beetles collected in a pitfall trap. Once the set of individuals has been defined, its species richness can be exactly quantified, provided the species-level Taxonomy (biology), taxo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mulde Event
The Mulde event was an anoxic event, and marked the second of three relatively minor mass extinctions (the Ireviken, Mulde, and Lau events) during the Silurian period. It coincided with a global drop in sea level, and is closely followed by an excursion in geochemical isotopes. Its onset is synchronous with the deposition of the Fröjel Formation in Gotland. Perceived extinction in the 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 ... fauna, however, likely represent a change in the depositional environment of sedimentary sequences rather than a genuine biological extinction. Higher resolution δ13C isotope analysis identifies differences in the organic and carbonate carbon isotope curves (Δ13C), allowing the inference of a sustained drop in CO2 levels coincident wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ireviken Event
The Ireviken event was the first of three relatively minor extinction events (the Ireviken, Mulde, and Lau events) during the Silurian period. It occurred at the Llandovery/ Wenlock boundary (mid Silurian, ). The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species became extinct; 80% of the global conodont species also became extinct in this interval. Anatomy of the event The event lasted around 200,000 years, spanning the base of the Wenlock epoch. It is associated with a period of global cooling. It comprises eight extinction "datum points"—the first four being regularly spaced, every 30,797 years, and linked to the Milankovic obliquity cycle. The fifth and sixth probably reflect maxima in the precessional cycles, with periods of around 16.5 and 19 ka. The final two data are much further spaced, so harder to link with Milankovic changes. Casualties The mechanism responsible for the event originated in the deep oceans, and made its way into the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalopods
A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symmetry, bilateral body symmetry, a prominent head, and a set of cephalopod arm, arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt Cephalopod ink, ink. The study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, Extant taxon, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by ''Nautilus (genus), Nautilus'' and ''Allonautilus''. In the Coleoidea, the molluscan shell has been internalized or is absent, where ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prasinophyte
The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives.Sym, S. D. and Pienaar, R. N. 1993. The class Prasinophyceae. In Round, F. E. and Chapman, D. J. (eds) ''Progress in Phycological Research'', Vol. 9. Biopress Ltd., Bristol, pp. 281-376. The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells, as well as dormant or cyst stage phycoma. The cells of many species are covered with organic body scales; others are naked. Well studied genera include '' Ostreococcus'', considered to be the smallest (ca. 0.95 μm) free-living eukaryote, and '' Micromonas'', both of which are found in marine waters worldwide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes (about 12 Mbp for '' Ostreococcus'' an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acritarchs
Acritarchs () are organic microfossils, known from the Precambrian to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion. Many acritarchs likely represent resting cysts of single-celled marine phytoplanktonic algae, similar to those produced by living dinoflagellates. Definition Acritarchs were originally defined as non-acid soluble (i.e. non-carbonate, non- siliceous) organic-walled microfossils consisting of a central cavity, and whose biological affinities cannot be determined with certainty. Most commonly they are composed of thermally altered acid insoluble carbon compounds (kerogen). Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small metazoans to resting cysts of many kinds of chlorophyta (green algae) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linguliform
Linguliformea is a subphylum of inarticulate brachiopods. These were the earliest of brachiopods, ranging from the Cambrian into the Holocene. They rapidly diversified during the Cambrian into the Ordovician, but most families became extinct by the end of the Devonian. The articulation in these brachiopods is lacking. These brachiopods have adductor and oblique muscles, but no diductor muscles. The anus is located at the side of the body. The pedicle is a hollow extension of the ventral body wall. Posterior body wall separates dorsal and ventral mantles. The shells are usually made up of apatite (calcium phosphate), however rare cases have calcite or aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ... shells. See also * References Brachiopod taxonomy Paleozoic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Machaeridia (annelid)
Machaeridia is an extinct group of armoured, segmented annelid worms, known from the Early Ordovician (Late Tremadoc) to Carboniferous. It consists of three distinct families: the plumulitids, turrilepadids and lepidocoleids. Fossils Only the calcitic sclerites ("armour plates") of these worms tend to be preserved in the fossil record. These are tiny, and usually found disarticulated: articulated specimens reach about a centimeter in length, and are incredibly rare – hence the limited degree of study since their description in 1857. The machaeridians are characterized by having serialized rows of calcitic shell plates. The dorsal sclerites were convex and almost isometric; lateral sclerites were flatter and longer. The plates comprised two calcite layers: the outer layer is thin and formed by lamellar deposition, whereas new elements were added to the thicker inner layer as it grew. Scales are ridged with growth lines, implying that they grew episodically. A few taxa experi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyolithids
Hyoliths are animals with small conical shells, known from fossils from the Palaeozoic era. They are at least considered as being lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods (hyoliths may even be brachiopods themselves), while others consider them as being basal lophotrochozoans, or even molluscs. Morphology The shell of a hyolith is typically one to four centimeters in length, triangular or elliptical in cross section. Some species have rings or stripes. It comprises two parts: the main conical shell (previously referred to as a ‘conch’) and a cap-like operculum. Some also had two curved supports known as ''helens'' They are calcareous – probably aragonitic All of these structures grew by marginal accretion. Shell microstructure The orthothecid shell has an internal layer with a microstructure of transverse bundles, and an external layer comprising longitudinal bundles. Helens Some hyoliths had helens, long structures ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobites
Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, existing in oceans for almost 270million years, with over 22,000 species having been described. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton made of calcite, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics. Trilobites are placed within the clade Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain. Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or filter feeders, and some swam, feeding o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crinoids
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 members of the largest crinoid order, Comatulida. Crinoids are echinoderms in the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. They live in both shallow water and in depths of over . Adult crinoids are characterised by having the mouth located on the upper surface. This is surrounded by feeding arms, and is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more. These have feathery pinnules and are spread wide to gather planktonic particles from the water. At some stage in their lives, most crinoids have a sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
