Cetaceans are aquatic mammals constituting the infraorder Cetacea. There are around 89 living species; the first is the Odontoceti, the toothed whales, which consist of around 70 species, including the dolphin, beluga whale, sperm whale, beaked whale. The second is the Mysticeti, the baleen whales, which have a filter-feeder system, consist of 15 species divided into 3 families, include the right whale, bowhead whale, pygmy right whale, gray whale; the ancient and extinct ancestors of modern whales lived 53 to 45 million years ago. They diverged from even-toed ungulates, they were amphibious, evolved in the shallow waters that separated India from Asia. Around 30 species adapted to a oceanic life. Baleen whales split from toothed whales around 34 million years ago; the smallest cetacean is Maui's dolphin, at 50 kg. Baleen whales have a tactile system in the short hairs around their mouth. Cetaceans have well-developed senses—their eyesight and hearing are adapted for both air and water, they have a layer of blubber, under the skin to maintain body heat in cold water.
Several species exhibit sexual dimorphism. Two external forelimbs are modified into flippers. Cetaceans have streamlined bodies: they can swim quickly, with the killer whale able to travel at 56 kilometres per hour in short bursts, the fin whale able to cruise at 48 kilometres per hour, dolphins able to make tight turns at high speeds, some species diving to great depths. Although cetaceans are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres, they spend their lives in the water of rivers. This has drastically affected their anatomy to be able to do so, they feed on fish and marine invertebrates. Some baleen whales are specialised for feeding on benthic creatures. Male cetaceans mate with more than one female, although the degree of polygyny varies with the species. Cetaceans are not known to have pair bonds. Male cetacean strategies for reproductive success vary between herding females, defending potential mates from other males, or whale song which attracts mates.
Calves are born in the fall and winter months, females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a short period of time, more typical of baleen whales as their main food source aren't found in their breeding and calving grounds. Cetaceans produce a number of vocalizations, notably the clicks and whistles of dolphins and the moaning songs of the humpback whale; the meat and oil of cetaceans have traditionally been used by indigenous peoples of the Arctic. Cetaceans have been depicted in various cultures worldwide. Dolphins are kept in captivity and are sometimes trained to perform tricks and tasks, other cetaceans aren't as kept in captivity. Cetaceans have been relentlessly hunted by commercial industries for their products, although this is now forbidden by international law; the baiji has become "Possibly Extinct" in the past century, while the vaquita and Yangtze finless porpoise are ranked Critically Endangered by the International Union for Conservation of Nature.
Besides hunting, cetaceans face threats from accidental trapping, marine pollution, ongoing climate change. The two parvorders, baleen whales and toothed whales, are thought to have diverged around thirty-four million years ago. Baleen whales have bristles made of keratin instead of teeth; the bristles filter other small invertebrates from seawater. Grey whales feed on bottom-dwelling mollusks. Rorqual family use throat pleats to expand their mouths to sieve out the water. Balaenids have massive heads. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of relying on their fat reserves; the parvorder of Odontocetes – the toothed whales – include sperm whales, beaked whales, killer whales and porpoises. The teeth are designed for catching fish, squid or other marine invertebrates, not for chewing them, so prey is swallowed whole. Teeth are shaped like cones, pegs, tusks or variable.
Female beaked whales' teeth are hidden in the gums and are not visible, most male beaked whales have only two short tusks. Narwhals have vestigial teeth other than their tusk, present on males and 15% of females and has millions of nerves to sense water temperature and salinity. A few toothed whales, such as some killer whales, feed on mammals, such as pinnipeds and other whales. Toothed whales have well-developed senses – their eyesight and hearing are adapted for both air and water, they have advan
Leiden is a city and municipality in the province of South Holland, Netherlands. The municipality of Leiden had a population of 123,856 in August 2017, but the city forms one densely connected agglomeration with its suburbs Oegstgeest, Leiderdorp and Zoeterwoude with 206,647 inhabitants; the Netherlands Central Bureau of Statistics further includes Katwijk in the agglomeration which makes the total population of the Leiden urban agglomeration 270,879, in the larger Leiden urban area Teylingen and Noordwijkerhout are included with in total 348,868 inhabitants. Leiden is located on the Oude Rijn, at a distance of some 20 kilometres from The Hague to its south and some 40 km from Amsterdam to its north; the recreational area of the Kaag Lakes lies just to the northeast of Leiden. A university city since 1575, Leiden has been one of Europe's most prominent scientific centres for more than four centuries. Leiden is a typical university city, university buildings are scattered throughout the city and the many students from all over the world give the city a bustling and international atmosphere.
Many important scientific discoveries have been made here, giving rise to Leiden's motto: ‘City of Discoveries’. The city houses Leiden University, the oldest university of the Netherlands, Leiden University Medical Center. Leiden University is one of Europe's top universities, with thirteen Nobel Prize winners, it is a member of the League of European Research Universities and positioned in all international academic rankings. It is twinned with the location of the United Kingdom's oldest university. Leiden University and Leiden University of Applied Sciences together have around 35,000 students. Modern scientific medical research and teaching started in the early 18th century in Leiden with Boerhaave. Leiden is a city with a rich cultural heritage, not only in science, but in the arts. One of the world's most famous painters, was born and educated in Leiden. Other famous Leiden painters include Jan van Goyen and Jan Steen. Leiden was formed on an artificial hill at the confluence of the rivers Nieuwe Rijn.
In the oldest reference to this, from circa 860, the settlement was called Leithon. The name is said to be from Germanic *leitha- "canal" in dative pluralis, thus meaning "at the canals". "Canal" is not the proper word. A leitha was a human-modified natural river natural artificial. Leiden has in the past erroneously been associated with the Roman outpost Lugdunum Batavorum; this particular castellum was thought to be located at the Burcht of Leiden, the city's name was thought to be derived from the Latin name Lugdunum. However the castellum was in fact closer to the town of Katwijk, whereas the Roman settlement near modern-day Leiden was called Matilo; the landlord of Leiden, situated in a stronghold on the hill, was subject to the Bishop of Utrecht but around 1100 the burgraves became subject to the county of Holland. This county got its name in 1101 from a domain near the stronghold: Holland. Leiden was sacked in 1047 by Emperor Henry III. Early 13th century, Countess of Holland took refuge here when she was fighting in a civil war against her uncle, William I, Count of Holland.
He captured Ada. Leiden received city rights in 1266. In 1389, its population had grown to about 4,000 persons. In 1420, during the Hook and Cod wars, Duke John III of Bavaria along with his army marched from Gouda in the direction of Leiden in order to conquer the city since Leiden did not pay the new Count of Holland Jacqueline, Countess of Hainaut, his niece and only daughter of Count William VI of Holland. Burgrave Filips of Wassenaar and the other local noblemen of the Hook faction assumed that the duke would besiege Leiden first and send small units out to conquer the surrounding citadels, but John of Bavaria chose to attack the citadels first. He rolled the cannons along with his army but one, too heavy went by ship. By firing at the walls and gates with iron balls the citadels fell one by one. Within a week John of Bavaria conquered the castles of Poelgeest, Ter Does, Hoichmade, de Zijl, ter Waerd, Warmond and de Paddenpoel. On 24 June the army appeared before the walls of Leiden. On 17 August 1420, after a two-month siege the city surrendered to John of Bavaria.
The burgrave Filips of Wassenaar was stripped of his offices and rights and lived out his last years in captivity. Leiden flourished in the 17th century. At the close of the 15th century the weaving establishments of Leiden were important, after the expulsion of the Spaniards Leiden cloth, Leiden baize and Leiden camlet were familiar terms. In the same period, Leiden developed an important publishing industry; the influential printer Christoffel Plantijn lived there at one time. One of his pupils was Lodewijk Elzevir, who established the largest bookshop and printing works in Leiden, a business continued by his descendants through 1712 and the name subsequently adopted by contemporary publisher Elsevier. In 1572, the city sided with the Dutch revolt against Spanish rule and played an important role in the Eighty Years' War. Besieged from May until October 1574 by the Spanish, Leiden was relieved by the cutting of the dikes, thus enabling ships to carry provisions to the inhabitants of the flooded town.
As a reward for the heroic defence of the previous year, the University of Leiden was founded by William I of Orange in 1575. Yearly on 3 Oc
Kala Chitta Range
Kala Chitta Range is a mountain range located in the Attock District of Punjab, Pakistan. The range thrusts eastward across the Potohar plateau towards Rawalpindi
The protocetids form a diverse and heterogeneous group of cetaceans known from Asia, Africa and North America. There were many genera, some of these are well known. Known protocetids had large fore- and hindlimbs that could support the body on land, it is that they lived amphibiously: in the sea and on land, it is unclear at present. However, what is clear is that they are adapted further to an aquatic life-style. In Rodhocetus, for example, the sacrum – a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis with the rest of the vertebral column – was divided into loose vertebrae. However, the pelvis was still connected to one of the sacral vertebrae. Furthermore, the nasal openings are now halfway up the snout, their supposed amphibious nature is supported by the discovery of a pregnant Maiacetus, in which the fossilised fetus was positioned for a head-first delivery, suggesting that Maiacetus gave birth on land. The ungulate ancestry of these early whales is still underlined by characteristics like the presence of hooves at the ends of toes in Rodhocetus.
The protocetid subfamilies were proposed by al.. 2005. They placed Makaracetus in its own subfamily based on its unique adaptations for feeding, they erected two subfamilies for the rest of the protocetids based on their degree of aquatic adaptation:Protocetinae- Protocetines are Lutetian protocetids with generalized skulls retaining three incisors in the premaxilla and three molars in the maxilla. To the extent postcrania are known, they have a pelvis similar to those in land-living mammals, with a sacrum composed of several fused vertebrae, articulated to the ilia and innominates, large hindlimbs used for foot-powered propulsion. Georgiacetinae- Georgiacetines are Bartonian protocetids transitional to the basilosaurids, their skulls and dentition is similar to those of protocetines, but their pelvis is reduced without substantial articulations between the sacrum and the ilia and innominates. No hindlimbs have been found, but the reduced pelvis indicates that they swam using their tail rather than their feet
A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
A continent is one of several large landmasses of the world. Identified by convention rather than any strict criteria, up to seven regions are regarded as continents. Ordered from largest in area to smallest, they are: Asia, North America, South America, Antarctica and Australia. Geologically, the continents correspond to areas of continental crust that are found on the continental plates. However, some areas of continental crust are regions covered with water not included in the list of continents. Zealandia is one such area. Islands are grouped with a neighbouring continent to divide all the world's land into geopolitical regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form a geopolitical region called Oceania. By convention, "continents are understood to be large, discrete masses of land, ideally separated by expanses of water." Several of the seven conventionally recognized continents are not discrete landmasses separated by water.
The criterion "large" leads to arbitrary classification: Greenland, with a surface area of 2,166,086 square kilometres is considered the world's largest island, while Australia, at 7,617,930 square kilometres is deemed the smallest continent. Earth's major landmasses all have coasts on a single, continuous World Ocean, divided into a number of principal oceanic components by the continents and various geographic criteria; the most restricted meaning of continent is that of a continuous area of land or mainland, with the coastline and any land boundaries forming the edge of the continent. In this sense the term continental Europe is used to refer to mainland Europe, excluding islands such as Great Britain, Ireland and Iceland, the term continent of Australia may refer to the mainland of Australia, excluding Tasmania and New Guinea; the continental United States refers to the 48 contiguous states and the District of Columbia in central North America and may include Alaska in the northwest of the continent, while excluding Hawaii, Puerto Rico, Guam in the oceans.
From the perspective of geology or physical geography, continent may be extended beyond the confines of continuous dry land to include the shallow, submerged adjacent area and the islands on the shelf, as they are structurally part of the continent. From this perspective, the edge of the continental shelf is the true edge of the continent, as shorelines vary with changes in sea level. In this sense the islands of Great Britain and Ireland are part of Europe, while Australia and the island of New Guinea together form a continent; as a cultural construct, the concept of a continent may go beyond the continental shelf to include oceanic islands and continental fragments. In this way, Iceland is considered Madagascar part of Africa. Extrapolating the concept to its extreme, some geographers group the Australian continental plate with other islands in the Pacific into one continent called Oceania; this divides the entire land surface of Earth into quasi-continents. The ideal criterion that each continent is a discrete landmass is relaxed due to historical conventions.
Of the seven most globally recognized continents, only Antarctica and Australia are separated from other continents by the ocean. Several continents are defined not as distinct bodies but as "more or less discrete masses of land". Asia and Africa are joined by the Isthmus of Suez, North and South America by the Isthmus of Panama. In both cases, there is no complete separation of these landmasses by water. Both these isthmuses are narrow compared to the bulk of the landmasses they unite. North America and South America are treated as separate continents in the seven-continent model. However, they may be viewed as a single continent known as America or the Americas; this viewpoint was common in the United States until World War II, remains prevalent in some Asian six-continent models. This remains the more common vision in Latin American countries, Portugal, Italy and Hungary where they are taught as a single continent; the criterion of a discrete landmass is disregarded if the continuous landmass of Eurasia is classified as two separate continents: Europe and Asia.
Physiographically and South Asia are peninsulas of the Eurasian landmass. However, Europe is considered a continent with its comparatively large land area of 10,180,000 square kilometres, while South Asia, with less than half that area, is considered a subcontinent; the alternative view—in geology and geography—that Eurasia is a single continent results in a six-continent view of the world. Some view separation of Eurasia into Asia and Europe as a residue of Eurocentrism: "In physical and historical diversity and India are comparable to the entire European landmass, not to a single European country.." However, for historical and cultural reasons, the view of Europe as a separate continent continues in several categorizations. If continents are defined as discrete landmasses, embracing all the contiguous land of a body Africa and Europe form a single continent which may be referred to as Afro-Eurasia; this produces a four-continent model consisting of Afro-Eurasia, America and Australia. When sea levels were lower during the Pleistocene ice ages, gre
Whales are a distributed and diverse group of aquatic placental marine mammals. They are an informal grouping within the infraorder Cetacea excluding dolphins and porpoises. Whales and porpoises belong to the order Cetartiodactyla with even-toed ungulates and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago; the two parvorders of whales, baleen whales and toothed whales, are thought to have split apart around 34 million years ago. The whales comprise eight extant families: Balaenopteridae, Cetotheriidae, Monodontidae, Physeteridae and Ziphiidae. Whales are creatures of the open ocean. So extreme is their adaptation to life underwater. Whales range in size from the 2.6 metres and 135 kilograms dwarf sperm whale to the 29.9 metres and 190 metric tons blue whale, the largest creature that has lived. The sperm whale is the largest toothed predator on earth. Several species exhibit sexual dimorphism. Baleen whales have no teeth, they use their throat pleats to expand the mouth to take in huge gulps of water.
Balaenids have heads. Toothed whales, on the other hand, have conical teeth adapted to catching squid. Baleen whales have a well developed sense of "smell", whereas toothed whales have well-developed hearing − their hearing, adapted for both air and water, is so well developed that some can survive if they are blind; some species, such as sperm whales, are well adapted for diving to great depths to catch squid and other favoured prey. Whales have evolved from land-living mammals; as such whales must breathe air although they can remain submerged under water for long periods of time. Some species such as the sperm whale are able to stay submerged for as much as 90 minutes, they have blowholes located on top of their heads, through which air is expelled. They are warm-blooded, have a layer of fat, or blubber, under the skin. With streamlined fusiform bodies and two limbs that are modified into flippers, whales can travel at up to 20 knots, though they are not as flexible or agile as seals. Whales produce a great variety of notably the extended songs of the humpback whale.
Although whales are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres, migrate to the equator to give birth. Species such as humpbacks and blue whales are capable of travelling thousands of miles without feeding. Males mate with multiple females every year, but females only mate every two to three years. Calves are born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species nurse their young for one to two years. Once relentlessly hunted for their products, whales are now protected by international law; the North Atlantic right whales nearly became extinct in the twentieth century, with a population low of 450, the North Pacific grey whale population is ranked Critically Endangered by the IUCN. Besides whaling, they face threats from bycatch and marine pollution; the meat and baleen of whales have traditionally been used by indigenous peoples of the Arctic. Whales have been depicted in various cultures worldwide, notably by the Inuit and the coastal peoples of Vietnam and Ghana, who sometimes hold whale funerals.
Whales feature in literature and film, as in the great white whale of Herman Melville's Moby Dick. Small whales, such as belugas, are sometimes kept in captivity and trained to perform tricks, but breeding success has been poor and the animals die within a few months of capture. Whale watching has become a form of tourism around the world; the word "whale" comes from the Old English whæl, from Proto-Germanic *hwalaz, from Proto Indo European *kwal-o-, meaning "large sea fish". The Proto-Germanic *hwalaz is the source of Old Saxon hwal, Old Norse hvalr, Swedish val, Middle Dutch wal, Dutch walvis, Old High German wal, German Wal; the obsolete "whalefish" has a similar derivation, indicating a time when whales were thought to be fish. Other archaic English forms include wal, whal, whaille, etc; the term "whale" is sometimes used interchangeably with dolphins and porpoises, acting as a synonym for Cetacea. Six species of dolphins have the word "whale" in their name, collectively known as blackfish: the killer whale, the melon-headed whale, the pygmy killer whale, the false killer whale, the two species of pilot whales, all of which are classified under the family Delphinidae.
Each species has a different reason for it, for example, the killer whale was named "Ballena asesina"'killer whale' by Spanish sailors. The term "Great Whales" covers those regulated by the International Whaling Commission: the Odontoceti family Physeteridae; the whales are part of the terrestrial mammalian clade Laurasiatheria. Whales do not form a order.