Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, pectoral fins that are not fused to the head. Modern sharks are the sister group to the rays. However, the term "shark" has been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans. Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are referred to as "spiny sharks". Since sharks have diversified into over 500 species, they range in size from the small dwarf lanternshark, a deep sea species of only 17 centimetres in length, to the whale shark, the largest fish in the world, which reaches 12 metres in length. Sharks are common to depths of 2,000 metres, they do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater.

Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth. Well-known species such as the tiger shark, blue shark, great white shark, mako shark, thresher shark, hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities; until the 16th century, sharks were known to mariners as "sea dogs". This is still evidential in the porbeagle; the etymology of the word "shark" is uncertain, the most etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk, meaning "villain, scoundrel", applied to the fish due to its predatory behaviour. A now disproven theory is that it derives from the Yucatec Maya word xok, meaning "fish". Evidence for this etymology came from the Oxford English Dictionary, which notes shark first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and posted "sharke" to refer to the large sharks of the Caribbean Sea.

However, the Middle English Dictionary records an isolated occurrence of the word shark in a letter written by Thomas Beckington in 1442, which rules out a New World etymology. Evidence for the existence of sharks dates from the Ordovician period, 450–420 million years ago, before land vertebrates existed and before a variety of plants had colonized the continents. Only scales have been recovered from the first sharks and not all paleontologists agree that these are from true sharks, suspecting that these scales are those of thelodont agnathans; the oldest accepted shark scales are from about 420 million years ago, in the Silurian period. The first sharks looked different from modern sharks. At this time the most common shark tooth is the cladodont, a style of thin tooth with three tines like a trident to help catch fish; the majority of modern sharks can be traced back to around 100 million years ago. Most fossils are of teeth in large numbers. Partial skeletons and complete fossilized remains have been discovered.

Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils. The teeth consist of fossilized calcium phosphate, an apatite; when a shark dies, the decomposing skeleton breaks up. Preservation requires rapid burial in bottom sediments. Among the most ancient and primitive sharks is Cladoselache, from about 370 million years ago, found within Paleozoic strata in Ohio and Tennessee. At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre long with stiff triangular fins and slender jaws, its teeth had several pointed cusps. From the small number of teeth found together, it is most that Cladoselache did not replace its teeth as as modern sharks, its caudal fins had a similar shape to the great white sharks and the pelagic shortfin and longfin makos. The presence of whole fish arranged tail-first in their stomachs suggest that they were fast swimmers with great agility.

Most fossil sharks from about 300 to 150 million years ago can be assigned to one of two groups. The Xenacanthida was exclusive to freshwater environments. By the time this group became extinct about 220 million years ago, they had spread worldwide; the other group, the hybodonts, appeared about 320 million years ago and lived in the oceans, but in freshwater. The results of a 2014 study of the gill structure of an unusually well preserved 325-million-year-old fossil suggested that sharks are not "living fossils", but rather have evolved more extensively than thought over the hundreds of millions of years they have been around. Modern sharks began to appear about 100 million years ago. Fossil mackerel shark teeth date to the Early Cretaceous. One of the most evolved families is the hammerhead shark, which emerged in the Eocene; the oldest white shark teeth date from 60 to 66 million years ago, around the time of the extinction of the dinosaurs. In early white shark evolution th


The Führerbunker was an air raid shelter located near the Reich Chancellery in Berlin, Germany. It was part of a subterranean bunker complex constructed in two phases in 1936 and 1944, it was the last of the Führer Headquarters used by Adolf Hitler during World War II. Hitler took up residence in the Führerbunker on 16 January 1945, it became the centre of the Nazi regime until the last week of World War II in Europe. Hitler married Eva Braun there on 29 April 1945. After the war, both the old and new Chancellery buildings were levelled by the Soviets; the underground complex remained undisturbed until 1988–89, despite some attempts at demolition. The excavated sections of the old bunker complex were destroyed during reconstruction of that area of Berlin; the site remained unmarked until 2006. Some corridors of the bunker still are sealed off from the public; the Reich Chancellery bunker was constructed as a temporary air-raid shelter for Hitler. Increased bombing of Berlin led to expansion of the complex as an improvised permanent shelter.

The elaborate complex consisted of two separate shelters, the Vorbunker, completed in 1936, the Führerbunker, located 2.5 metres lower than the Vorbunker and to the west-southwest, completed in 1944. They were connected by a stairway set at right angles and could be closed off from each other by a bulkhead and steel door; the Vorbunker was located 1.5 metres beneath the cellar of a large reception hall behind the old Reich Chancellery at Wilhelmstrasse 77. The Führerbunker was located about 8.5 metres beneath the garden of the old Reich Chancellery, 120 metres north of the new Reich Chancellery building at Voßstraße 6. Besides being deeper under ground, the Führerbunker had more reinforcement, its roof was made of concrete 3 metres thick. About 30 small rooms were protected by 4 metres of concrete; the Führerbunker development was built by the Hochtief company as part of an extensive program of subterranean construction in Berlin begun in 1940. Hitler's accommodations were in this newer, lower section, by February 1945 it had been decorated with high-quality furniture taken from the Chancellery, along with several framed oil paintings.

After descending the stairs into the lower section and passing through the steel door, there was a long corridor with a series of rooms on each side. On the right side were a series of rooms which included generator/ventilation rooms and the telephone switchboard. On the left side was Eva Braun's bedroom/sitting room, an ante-chamber, which led into Hitler's study/office. On the wall hung a large portrait of Frederick the Great, one of Hitler's heroes. A door led into Hitler's modestly furnished bedroom. Next to it was the conference/map room which had a door that led out into the waiting room/ante-room; the bunker complex was self-contained. However, as the Führerbunker was below the water table, conditions were unpleasantly damp, with pumps running continuously to remove groundwater. A diesel generator provided electricity, well water was pumped in as the water supply. Communications systems included a telex, a telephone switchboard, an army radio set with an outdoor antenna; as conditions deteriorated at the end of the war, Hitler received much of his war news from BBC radio broadcasts and via courier.

Hitler moved into the Führerbunker on 16 January 1945, joined by his senior staff, including Martin Bormann. Eva Braun and Joseph Goebbels joined them in April, while Magda Goebbels and their six children took residence in the upper Vorbunker. Two or three dozen support and administrative staff were sheltered there; these included Hitler's secretaries, a nurse named Erna Flegel, telephone switchboard operator Sergeant Rochus Misch. Hitler continued to utilize the undamaged wing of the Reich Chancellery, where he held afternoon military conferences in his large study. Afterwards, he would have tea with his secretaries before returning to the bunker complex for the night. After several weeks of this routine, Hitler left the bunker except for short strolls in the chancellery garden with his dog Blondi; the bunker was crowded, the atmosphere was oppressive, air raids occurred daily. Hitler stayed on the lower level, where it was quieter and he could sleep. Conferences took place for much of the night until 05:00.

On 16 April, the Red Army started the Battle of Berlin, they started to encircle the city by 19 April. Hitler made his last trip to the surface on 20 April, his 56th birthday, going to the ruined garden of the Reich Chancellery where he awarded the Iron Cross to boy soldiers of the Hitler Youth; that afternoon, Berlin was bombarded by Soviet artillery for the first time. Hitler was in denial about the dire situation and placed his hopes on the units commanded by Waffen-SS General Felix Steiner, the Armeeabteilung Steiner. On 21 April, Hitler ordered Steiner to attack the northern flank of the encircling Soviet salient and ordered the German Ninth Army, south-east of Berlin, to attack northward in a pincer attack; that evening, Red Army tanks reached the outskirts of Berlin. Hitler was told at his afternoon situation conference on 22 April that Steiner's forces had not moved, he fe

Individual Freedoms and Equality Committee (Tunisia)

The Individual Freedoms and Equality Committee is a commission created by the president of Tunisia Beji Caid Essebsi on 13 August 2017. The committee is in charge of preparing a report on legislative reforms concerning individual freedoms and equality in accordance with the Constitution of 2014 and international human rights standards; the committee is charged with contributing to the state of individual freedoms and equality in Tunisia through the preparation of a reform project in accordance with the requirements of the Tunisian Constitution of 2014 and international human rights standards. Indeed, the Constitution includes a number of chapters on individual freedoms and the principles of equality, while many legislation and laws inherited from the French protectorate and the dictatorship are incompatible with the principles and spirit of contained changes; the Individual Freedoms and Equality Committee is composed of nine members: The work started since the first day, on the 14 August 2017, the committee has drawn up an inventory of laws that undermine individual freedoms and equality and which are not in conformity with the Constitution and commitments of Tunisia in terms of human rights before entering in the proposal formulation phase.

The committee has chosen to adopt a participative and consultative approach by inviting public life actors to contribute to the project. Through this approach, political parties represented in the Assembly of the Representatives of the People and government, specialized civil society organizations, academics specializing in several disciplines were consulted and their contributions helped to move the work of the committee forward significantly. Official website