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Whales are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are linked to the Indohyus, an wiped out chevrotain-like ungulate, from which they will split approximately 48 million years ago.|19||20| Primitive cetaceans, or archaeocetes, first took to the sea roughly 49 million years ago and became fully aquatic 5-10 mil years later. What specifies an archaeocete is the existence of anatomical features unique to cetaceans, alongside other primitive features not present in modern cetaceans, such as noticeable legs or asymmetrical teeth.|21||22||23||9| Their features became adapted for living in the marine environment. Major anatomical changes included their hearing set-up that channeled shocks from the jaw to the earbone (Ambulocetus 49 mya), a streamlined body and the growth of flukes on the tail (Protocetus 43 mya), the migration of the nostrils toward the very best of the cranium (blowholes), plus the modification of the forelimbs into flippers (Basilosaurus 35 mya), and the shrinking and eventual disappearance of the hind arms and legs (the first odontocetes and mysticetes 34 mya).|24||25||26|
Whale morphology shows a number of examples of concourant evolution, the most obvious being the streamlined fish-like body shape.|27| Other examples include the application of echolocation for hunting in low light conditions - which can be the same hearing adaptation utilized by bats - and, inside the rorqual whales, jaw different types, similar to those found in pelicans, that enable engulfment feeding.|28|
Today, the best living relatives of cetaceans are the hippopotamuses; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 mya.|9| Around 40 mya, a common ancestor between the two branched off into cetacea and anthracotheres; nearly all anthracotheres became extinct at the end on the Pleistocene 2 . 5 mya, eventually leaving only one living through lineage - the hippopotamus.|29|
Whales split into two separate parvorders around thirty four mya - the baleen whales (Mysticetes) and the toothed whales (Odontocetes).
Whales have torpedo shaped bodies with non-flexible necks, arms and legs modified into flippers, non-existent external ear flaps, a huge tail fin, and flat heads (with the exception to this rule of monodontids and ziphiids). Whale skulls have small eye orbits, long snouts (with the exception of monodontids and ziphiids) and eyes placed on the edges of its head. Whales range in size from the installment payments on your 6-metre (8. 5 ft) and 135-kilogram (298 lb) dwarf sperm whale for the 34-metre (112 ft) and 190-metric-ton (210-short-ton) blue whale. Overall, they tend to little other cetartiodactyls; the black whale is the largest animal on earth. Several species own female-biased sexual dimorphism, together with the females being larger than the males. One exception is to use the sperm whale, which includes males larger than the females.|33||34|
Odontocetes, like the sperm whale, possess pearly whites with cementum cells overlying dentine cells. Unlike individual teeth, which are composed mainly of enamel on the portion of the tooth outside of the gum, whale teeth own cementum outside the gum. Only in larger whales, the place that the cementum is worn away on the tip of the enamel, does enamel show. Mysticetes have large whalebone, instead of teeth, made of keratin. Mysticetes have two blowholes, whereas Odontocetes contain only one.|35|
Breathing involves expelling old air from the blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs; a humpback whale's lungs can hold about a few, 000 litres of air. Spout shapes differ amongst species, which facilitates detection.|36||37|
The cardiovascular system of a whale weighs regarding 180-200 kg. It is 640 times bigger than a human heart. The heart of the rare whale is the largest of any animal,|38| and the walls of the blood vessels in the heart have been referred to as being "as thick as an iPhone 6 Plus is definitely long".|39|
All whales have a thick covering of blubber. In kinds that live near the poles, the blubber can be as thick as 11 inches. This blubber can help with buoyancy (which is helpful for a 100-ton whale), safeguard to some extent as predators could have a hard time getting through a thick layer of fat, and energy for fasting the moment migrating to the equator; the principal usage for blubber can be insulation from the harsh climate. It can constitute as much as 50 percent of a whale's body weight. Legs are born with only a thin layer of blubber, however, many species compensate for this with thick lanugos.|40||41|
Whales have a two- to three-chambered stomach that may be similar in structure to terrestrial carnivores. Mysticetes contain a proventriculus as an extension with the oesophagus; this contains pebbles that grind up meals. They also have fundic and pyloric chambers.
Whales have two flippers within the front, and a tail fin. These flippers contain four digits. Although whales do not possess fully developed hind limbs, some, such as the sperm whale and bowhead whale, possess discrete rudimentary muscles, which may contain feet and digits. Whales are fast swimmers in comparison to seals, which will typically cruise at 5-15 kn, or 9-28 kilometres per hour (5. 6-17. 4 mph); the fin whale, in comparison, can travel for speeds up to 47 kms per hour (29 mph) plus the sperm whale can reach speeds of 35 kilometres per hour (22 mph). The fusing of the neck vertebrae, while increasing stability when ever swimming at high rates, decreases flexibility; whales are not able to turn their heads. Once swimming, whales rely on the tail fin propel them through the water. Flipper movements is continuous. Whales swimming by moving their tail fin and lower overall body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Some species log from the water, which may allow them to travel around faster. Their skeletal anatomy allows them to be fast swimmers. Most species own a dorsal fin.|43||44|
Whales are adapted for diving to superb depths. In addition to their streamlined bodies, they can slow their heart rate to conserve oxygen; blood vessels is rerouted from cells tolerant of water pressure to the heart and human brain among other organs; haemoglobin and myoglobin store air in body tissue; plus they have twice the concentration of myoglobin than haemoglobin. Before going on long divine, many whales exhibit a behaviour known as sounding; they will stay close to the surface for any series of short, shallow dives while building their fresh air reserves, and then make a sound dive.
The whale ear has certain adaptations to the marine environment. In humans, the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is absolutely no great difference between the outside and inner environments. Rather than sound passing through the outer head to the middle ear, whales receive sound through the neck, from which it passes through a low-impedance fat-filled cavity towards the inner ear.|46| The whale ear is certainly acoustically isolated from the head by air-filled sinus wallets, which allow for greater online hearing underwater.|47| Odontocetes send out high frequency clicks from an organ known as a melon. This melon involves fat, and the skull of any such creature containing a melon will have a large depressive disorder. The melon size varies between species, the bigger the more dependent they are of it. A beaked whale for example provides a small bulge sitting along with its skull, whereas a sperm whale's head is filled up mainly with the melons.|48||49||50||51|
The whale eye is actually small for its size, but they do retain a good degree of eyesight. As well as this, the eyes of a whale are placed on the sides of the head, so their vision consists of two fields, rather than binocular view like humans have. When belugas surface, their lens and cornea correct the nearsightedness which will result from the refraction of light; they contain both rod and cone cells, meaning they can see in both poor and bright light, but they include far more rod cells than they do cone cells. Whales do, however , lack brief wavelength sensitive visual colors in their cone cells producing a more limited capacity for shade vision than most mammals.|52| Most whales have slightly flattened eyeballs, enlarged pupils (which get smaller as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of sunshine to pass through the eye and, consequently , a very clear image of the surrounding area. They also have glands in the eyelids and outer corneal layer that act as protection for the cornea.|53||54|
The olfactory flambeau are absent in toothed whales, suggesting that they have zero sense of smell. Some whales, like the bowhead whale, possess a vomeronasal organ, which does show that they can "sniff out" krill.|55|
Whales are not thought to have a good sense of taste, as their taste buds will be atrophied or missing entirely. However , some toothed whales have preferences between different types of fish, indicating some sort of attachment to taste. The existence of the Jacobson's organ suggests that whales can stink food once inside their oral cavity, which might be similar to the sensation of taste.
2019-02-13 17:00:42 * 2019-02-10 13:01:42
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