Brachiopods, phylum Brachiopoda, are a group of lophotrochozoan animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized and inarticulate; the word "articulate" is used to describe the tooth-and-groove features of the valve-hinge, present in the articulate group, absent from the inarticulate group. This is the leading diagnostic feature, by which the two main groups can be distinguished. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two valves aligned. In a typical brachiopod a stalk-like pedicle projects from an opening in one of the valves near the hinges, known as the pedicle valve, keeping the animal anchored to the seabed but clear of silt that would obstruct the opening.
The word "brachiopod" is formed from podos. They are known as "lamp shells", since the curved shells of the class Terebratulida look rather like pottery oil-lamps. Lifespans range from three to over thirty years. Ripe gametes float from the gonads into the main coelom and exit into the mantle cavity; the larvae of inarticulate brachiopods are miniature adults, with lophophores that enable the larvae to feed and swim for months until the animals become heavy enough to settle to the seabed. The planktonic larvae of articulate species do not resemble the adults, but rather look like blobs with yolk sacs, remain among the plankton for only a few days before leaving the water column upon metamorphosing. In addition to the traditional classification of brachiopods into inarticulate and articulate, two approaches appeared in the 1990s: one approach groups the inarticulate Craniida with articulate brachiopods, since both use the same material in the mineral layers of their shell. However, some taxonomists believe it is premature to suggest higher levels of classification such as order and recommend a bottom-up approach that identifies genera and groups these into intermediate groups.
Traditionally, brachiopods have been regarded as members of, or as a sister group to, the deuterostomes, a superphylum that includes chordates and echinoderms. One type of analysis of the evolutionary relationships of brachiopods has always placed brachiopods as protostomes while another type has split between placing brachiopods among the protostomes or the deuterostomes, it was suggested in 2003 that brachiopods had evolved from an ancestor similar to Halkieria, a slug-like Cambrian animal with "chain mail" on its back and a shell at the front and rear end. However, new fossils found in 2007 and 2008 showed that the "chain mail" of tommotiids formed the tube of a sessile animal. Lineages of brachiopods that have both fossil and extant taxa appeared in the early Cambrian and Carboniferous periods, respectively. Other lineages have arisen and become extinct, sometimes during severe mass extinctions. At their peak in the Paleozoic era, the brachiopods were among the most abundant filter-feeders and reef-builders, occupied other ecological niches, including swimming in the jet-propulsion style of scallops.
Brachiopod fossils have been useful indicators of climate changes during the Paleozoic. However, after the Permian–Triassic extinction event, brachiopods recovered only a third of their former diversity. A study in 2007 concluded the brachiopods were vulnerable to the Permian–Triassic extinction, as they built calcareous hard parts and had low metabolic rates and weak respiratory systems, it was thought that brachiopods went into decline after the Permian–Triassic extinction, were out-competed by bivalves, but a study in 1980 found both brachiopod and bivalve species increased from the Paleozoic to modern times, with bivalves increasing faster. Brachiopods live only in the sea, most species avoid locations with strong currents or waves; the larvae of articulate species settle in and form dense populations in well-defined areas while the larvae of inarticulate species swim for up to a month and have wide ranges. Brachiopods now live in cold water and low light. Fish and crustaceans seem to find brachiopod flesh distasteful and attack them.
Among brachiopods, only the lingulids have been fished commercially, on a small scale. One brachiopod species may be a measure of environmental conditions around an oil terminal being built in Russia on the shore of the Sea of Japan. Modern brachiopods range from 1 to 100 millimetres long, most species are about 10 to 30 millimetres; the largest brachiopods known – Gigantoproductus and Titanaria, reaching 30 to 38 centimetres in width – occurred in the upper part of the Lower Carboniferous. Each has two valves which cover the dorsal and ventral surface of the animal, unlike bivalve molluscs whose shells cover the lateral surfaces; the valves are t
Estonia the Republic of Estonia, is a country in North East Europe. It is bordered to the north by the Gulf of Finland with Finland on the other side, to the west by the Baltic Sea with Sweden on the other side, to the south by Latvia, to the east by Lake Peipus and Russia; the territory of Estonia consists of a mainland and 2,222 islands in the Baltic Sea, covering a total area of 45,227 km2, water 2,839 km2, land area 42,388 km2, is influenced by a humid continental climate. The official language of the country, Estonian, is the third most spoken Finno-Ugric language; the territory of Estonia has been inhabited since at least 9,000 B. C. Ancient Estonians were some of the last European pagans to be Christianized, following the Livonian Crusade in the 13th century. After centuries of successive rule by Germans, Swedes and Russians, a distinct Estonian national identity began to emerge in the 19th and early 20th centuries; this culminated in independence from Russia in 1920 after a brief War of Independence at the end of World War I.
Democratic, after the Great Depression Estonia was governed by authoritarian rule since 1934 during the Era of Silence. During World War II, Estonia was contested and occupied by the Soviet Union and Germany being incorporated into the former as the Estonian Soviet Socialist Republic. After the loss of its de facto independence, Estonia's de jure state continuity was preserved by diplomatic representatives and the government-in-exile. In 1987 the peaceful Singing Revolution began against Soviet rule, resulting in the restoration of de facto independence on 20 August 1991; the sovereign state of Estonia is a democratic unitary parliamentary republic divided into fifteen counties. Its capital and largest city is Tallinn. With a population of 1.3 million, it is one of the least-populous member states of the European Union since joining in 2004, the economic monetary Eurozone, Organisation for Economic Co-operation and Development, Schengen Area, of the Western military alliance of the North Atlantic Treaty Organization.
It is a developed country with an advanced, high-income economy, among the fastest-growing in the EU. Estonia ranks high in the Human Development Index, performs favourably in measurements of economic freedom, civil liberties and press freedom. Estonian citizens are provided with universal health care, free education, the longest-paid maternity leave in the OECD. One of the world's most digitally advanced societies, in 2005 Estonia became the first state to hold elections over the Internet, in 2014 the first state to provide e-residency. In the Estonian language the oldest known endonym of the Estonians was maarahvas, meaning "country people" or "people of the soil"; the land inhabited by Estonians was called Maavald meaning "Country Realm" or "Land Realm". One hypothesis regarding the modern name of Estonia derives it from the Aesti, a people described by the Roman historian Tacitus in his Germania; the historic Aesti were Baltic people, whereas the modern Estonians are Finno-Ugric. The geographical areas of the Aesti and of Estonia do not match, with the Aesti living farther south.
Ancient Scandinavian sagas refer to an area called Eistland, as the country is still called in Icelandic, with close parallels to the Danish, Dutch and Norwegian terms Estland for the country. Early Latin and other ancient versions of the name include Hestia. Esthonia was a common alternative English spelling before 1921. Human settlement in Estonia became possible 13,000 to 11,000 years ago, when the ice from the last glacial era melted; the oldest known settlement in Estonia is the Pulli settlement, on the banks of the river Pärnu, near the town of Sindi, in south-western Estonia. According to radiocarbon dating it was settled around 11,000 years ago; the earliest human inhabitation during the Mesolithic period is connected to the Kunda culture, named after the town of Kunda in northern Estonia. At that time the country was covered with forests, people lived in semi-nomadic communities near bodies of water. Subsistence activities consisted of hunting and fishing. Around 4900 BC appear ceramics of the neolithic period, known as Narva culture.
Starting from around 3200 BC the Corded Ware culture appeared. The Bronze Age started around 1800 BC, saw the establishment of the first hill fort settlements. A transition from hunting-fishing-gathering subsistence to single-farm-based settlement started around 1000 BC, was complete by the beginning of the Iron Age around 500 BC; the large amount of bronze objects indicate the existence of active communication with Scandinavian and Germanic tribes. A more troubled and war-ridden middle Iron Age followed, with external threats appearing from different directions. Several Scandinavian sagas referred to major confrontations with Estonians, notably when Estonians defeated and killed the Swedish king Ingvar. Similar threats appeared in the east. In 1030 Yaroslav the Wise established a fort in modern-day Tartu. Around the 11th century, the Scandinavian Viking era around the Baltic Sea was succeeded by the Baltic Viking era, with seaborne
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 million years old, it is one of the earliest fossil beds containing soft-part imprints; the rock unit is a black shale and crops out at a number of localities near the town of Field in Yoho National Park and the Kicking Horse Pass. Another outcrop is in Kootenay National Park 42 km to the south; the Burgess Shale was discovered by palaeontologist Charles Walcott on 30 August 1909, towards the end of the season's fieldwork. He returned in 1910 with his sons and wife, establishing a quarry on the flanks of Fossil Ridge; the significance of soft-bodied preservation, the range of organisms he recognised as new to science, led him to return to the quarry every year until 1924. At that point, aged 74, he had amassed over 65,000 specimens. Describing the fossils was a vast task, pursued by Walcott until his death in 1927.
Walcott, led by scientific opinion at the time, attempted to categorise all fossils into living taxa, as a result, the fossils were regarded as little more than curiosities at the time. It was not until 1962 that a first-hand reinvestigation of the fossils was attempted, by Alberto Simonetta; this led scientists to recognise that Walcott had scratched the surface of information available in the Burgess Shale, made it clear that the organisms did not fit comfortably into modern groups. Excavations were resumed at the Walcott Quarry by the Geological Survey of Canada under the persuasion of trilobite expert Harry Blackmore Whittington, a new quarry, the Raymond, was established about 20 metres higher up Fossil Ridge. Whittington, with the help of research students Derek Briggs and Simon Conway Morris of the University of Cambridge, began a thorough reassessment of the Burgess Shale, revealed that the fauna represented were much more diverse and unusual than Walcott had recognized. Indeed, many of the animals present had bizarre anatomical features and only the slightest resemblance to other known animals.
Examples include Opabinia, with five eyes and a snout like a vacuum cleaner hose and Hallucigenia, reconstructed upside down, walking on bilaterally symmetrical spines. With Parks Canada and UNESCO recognising the significance of the Burgess Shale, collecting fossils became politically more difficult from the mid-1970s. Collections continued to be made by the Royal Ontario Museum; the curator of invertebrate palaeontology, Desmond Collins, identified a number of additional outcrops, stratigraphically both higher and lower than the original Walcott quarry. These localities continue to yield new organisms faster. Stephen Jay Gould's book Wonderful Life, published in 1989, brought the Burgess Shale fossils to the public's attention. Gould suggests that the extraordinary diversity of the fossils indicates that life forms at the time were much more disparate in body form than those that survive today, that many of the unique lineages were evolutionary experiments that became extinct. Gould's interpretation of the diversity of Cambrian fauna relied on Simon Conway Morris's reinterpretation of Charles Walcott's original publications.
However, Conway Morris disagreed with Gould's conclusions, arguing that all the Cambrian fauna could be classified into modern day phyla. The Burgess Shale has attracted the interest of paleoclimatologists who want to study and predict long-term future changes in Earth's climate. According to Peter Ward and Donald Brownlee in the 2003 book The Life and Death of Planet Earth, climatologists study the fossil records in the Burgess Shale to understand the climate of the Cambrian explosion, use it to predict what Earth's climate would look like 500 million years in the future when a warming and expanding Sun combined with declining CO2 and oxygen levels heat the Earth toward temperatures not seen since the Archean Eon 3 billion years ago, before the first plants and animals appeared, therefore understand how and when the last living things will die out. See Future of the Earth. After the Burgess Shale site was registered as a World Heritage Site in 1980, it was included in the Canadian Rocky Mountain Parks WHS designation in 1984.
In February 2014, the discovery was announced of another Burgess Shale outcrop in Kootenay National Park to the south. In just 15 days of field collecting in 2013, 50 animal species were unearthed at the new site; the fossil-bearing deposits of the Burgess Shale correlate to the Stephen Formation, a collection of calcareous dark mudstones, about 508 million years old. The beds were deposited at the base of a cliff about 160 m tall, below the depth agitated by waves during storms; this vertical cliff was composed of the calcareous reefs of the Cathedral Formation, which formed shortly before the deposition of the Burgess Shale. The precise formation mechanism is not known for certain, but the most accepted hypothesis suggests that the edge of the Cathedral Formation reef became detached from the rest of the reef and being transported some distance — kilometers — away from the reef edge. Reactivation of faults at the base of the formation led to its disintegration from about 509 million years ago.
This would have left a steep cliff, the bottom of which would be protected from tectonic decompression because the limestone of the Cathedral Formation is difficult to compress. This protection explains why fossils preserved further from the Cathedral Formation are impossible to work with — tectonic squeezing of the beds has produced a vertical cleavage that fractures the rocks, so they split perpendicular to the fossils; the Walcott quarry
The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia; the seas were warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w
Brachiozoa is a grouping of lophophorate animals including Brachiopoda and Phoronida
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix. Lagerstätten span geological time from the Neoproterozoic era to the present. Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan shales and Burgess Shale, the Devonian Hunsrück Slates and Gogo Formation, the Carboniferous Mazon Creek, the Jurassic Solnhofen limestone, the Cretaceous Santana and Tanis formations, the Eocene Green River Formation. Palaeontologists distinguish two kinds: Konzentrat-Lagerstätten are deposits with a particular "concentration" of disarticulated organic hard parts, such as a bone bed; these Lagerstätten are less spectacular than the more famous Konservat-Lagerstätten.
Their contents invariably display a large degree of time averaging, as the accumulation of bones in the absence of other sediment takes some time. Deposits with a high concentration of fossils that represent an in situ community, such as reefs or oyster beds, are not considered Lagerstätten. Konservat-Lagerstätten are deposits known for the exceptional preservation of fossilized organisms or traces; the individual taphonomy of the fossils varies with the sites. Conservation Lagerstätten are crucial in providing answers to important moments in the history and evolution of life. For example, the Burgess Shale of British Columbia is associated with the Cambrian explosion, the Solnhofen limestone with the earliest known bird, Archaeopteryx. Konservat-Lagerstätten preserve sclerotized and soft-bodied organisms or traces of organisms that are not otherwise preserved in the usual shelly and bony fossil record. In 1986, Simon Conway Morris calculated only about 14% of genera in the Burgess Shale had possessed biomineralized tissues in life.
The affinities of the shelly elements of conodonts were mysterious until the associated soft tissues were discovered near Edinburgh, Scotland, in the Granton Lower Oil Shale of the Carboniferous. Information from the broader range of organisms found in Lagerstätten have contributed to recent phylogenetic reconstructions of some major metazoan groups. Lagerstätten seem to be temporally autocorrelated because global environmental factors such as climate might affect their deposition. A number of taphonomic pathways may produce Lagerstätten; the following is an incomplete list: Orsten-type and Doushantuo-type preservations preserve organisms in phosphate. Bitter Springs-type preservation preserves them in silica. Carbonaceous films are the result of Burgess Shale-type preservation Pyrite preserves exquisite detail in Beecher’s trilobite-type preservation. Ediacaran-type preservation preserves moulds with the aid of microbial mats; the world's major Lagerstätten include: List of fossil sites Penney, D. 2010.
Biodiversity of Fossils in Amber from the Major World Deposits. Siri Scienfic Press, Manchester, 304 pp. "Fossil Lagerstätten". Department of Earth Sciences, University of Bristol. 2003. Retrieved 2005-11-21. – A catalogue of sites of exceptional fossil preservation produced by MSc palaeobiology students at University of Bristol's Department of Earth Sciences. Orr, Patrick J.. "Three-dimensional preservation of a non-biomineralized arthropod in concretions in Silurian volcaniclastic rocks from Herefordshire, England". Journal of the Geological Society. 157: 173–86. Doi:10.1144/jgs.157.1.173. Retrieved 2006-10-26
The Sipuncula or Sipunculida is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms. The name Sipuncula is from the genus name Sipunculus, comes from the Latin siphunculus meaning a "small tube". Traditionally considered a phylum, Sipuncula seems to be related to Myzostomida and Annelida, may be a subgroup of Annelida, based on recent molecular work. Sipunculans vary in size but most species are under 10 cm in length; the body is divided into an unsegmented, bulbous trunk and a narrower, anterior section, called the "introvert", which can be retracted into the trunk. The mouth is at the tip of the introvert and is surrounded in most groups by a ring of short tentacles. With no hard parts, the body is mobile. Although found in a range of habitats throughout the world's oceans, the majority of species live in shallow water habitats, burrowing under the surface of sandy and muddy substrates. Others live in rock crevices or in other concealed locations. Most sipunculans are deposit feeders, extending the introvert to gather food particles and draw them into the mouth, retracting the introvert when feeding conditions are unsuitable or danger threatens.
With a few exceptions, reproduction involves a planktonic larval stage. Sipunculid worms are used as food in some countries in southeast Asia; the Swedish naturalist Carl Linnaeus first described the worm Sipunculus nudus in his Systema naturae in 1767. In 1814, the French zoologist Constantine Samuel Rafinesque used the word "Sipuncula" to describe the family, in time, the term came to be used for the whole phylum; this is a understudied group, it is estimated there may be around 162 species worldwide. The phylogenetic placement of this phylum in the past has proved troublesome. Classified as annelids, despite the complete lack of segmentation and other annelid characters, the phylum Sipuncula was allied with the Mollusca on the basis of developmental and larval characters; these two phyla have been included in a larger group, the Lophotrochozoa, that includes the annelids, the ribbon worms and several other phyla. Phylogenetic analyses based on 79 ribosomal proteins indicated a position of Sipuncula within Annelida.
Subsequent analysis of the mitochondrion's DNA has confirmed their close relationship to the Myzostomida and Annelida. It has been shown that a rudimentary neural segmentation similar to that of annelids occurs in the early larval stage if these traits are absent in the adults. Sipunculans are worm-like animals ranging from 2 to 720 mm in length, with most species being under 10 cm; the sipunculan body is divided into an unsegmented, bulbous trunk and a narrower, anterior section, called the "introvert". Sipunculans have a body wall somewhat similar to that of annelids in that it consists of an epidermis without cilia overlain by a cuticle, an outer layer of circular and an inner layer of longitudinal musculature; the body wall surrounds the coelom, filled with fluid on which the body wall musculature acts as a hydrostatic skeleton to extend or contract the animal. When threatened, Sipunculid worms can contract their body into a shape resembling a peanut kernel—a practice that has given rise to the name "peanut worm".
The introvert is pulled inside the trunk by two pairs of retractor muscles that extend as narrow ribbons from the trunk wall to attachment points in the introvert. It can be protruded from the trunk by contracting the muscles of the trunk wall, thus forcing the fluid in the body cavity forwards; the introvert can vary in size from half the length of the trunk to several times its length, but whatever their comparative sizes, it is retractable. The mouth is located at the anterior end of the animal; the tentacles each have a deep groove along. They are used to gather organic detritus from the water or substrate, also function as gills. In the family Themistidae the tentacles form an elaborate crown-like structure, the members of this group being specialized filter feeders, unlike the other groups of sipunculans which are deposit feeders; the tentacles are hollow and are extended via hydrostatic pressure in a similar manner as the introvert, but have a different mechanism from that of the rest of the introvert, being connected, via a system of ducts, to one or two contractile sacs next to the oesophagus.
Hooks are present near the mouth on the introvert. These are proteinaceous, non-chitinous specializations of the epidermis, either arranged in rings or scattered, they may be involved in scraping algae off rock, or alternatively provide anchorage. Three genera in the Aspidosiphonidae family possess epidermal structures, known as anal and caudal shields; these are patches of thickened, hard plates, are used for boring into rock. In Aspidosiphon and Lithacrosiphon the anal shield is restricted to the dorsal side, causing the introvert to emerge at an angle, whereas it surrounds the anterior trunk in Cloeosiphon with the introvert emerging from its center. In Aspidosiphon the shield is a hardened, horny structure.