Marine mammal

As marine mammals, all mammals are referred to, have adapted back to life in the sea. Their ancestors were land-dwelling mammals. Among the whale fall (to which the dolphins are counted) to seals, manatees, and sea otters. While the seals still partially live on land and can move there as well, this is the whales and manatees no longer possible. The groups are not closely related to each other. The adaptations to the marine life span multiple convergent feature of training. So with all of these groups, the forelimbs are converted into paddle-like flippers, while the hind legs either completely lost (whales, manatees ) or be merged in the water to form a single tail fin (seals ). In addition, a nearly complete loss of hair, the formation of extensive subcutaneous fat, and changes of the respiratory system in order to perform long dives. Depending on the definition can also be counted the polar bear as the largest living land predator on marine mammals, because it is adapted to a large extent on the marine habitat.

Water habitat

The sea represents a habitat that differs significantly from the country and represents the living organisms in it special requirements. Accordingly, it comes in organisms that have gone into the sea in the course of evolution from country to various adjustments, without which this way of life would not be possible.

Locomotion

Most land animals can more or less swim well in permanently aquatic animals this basic skill is often accompanied by changes of the limbs and other body parts. So make very many of these species from webbed toes and fingers, which allow a greater displacement of the water. Webbed be found within the mammalian example, the Australian platypus, various rodents such as the beaver, insectivores such as the Desmanen or predators such as otters. Also for locomotion in the water and at the same time to control some of these animals have a modified tail rudder such as the beaver; In addition, all wasserbewohnenden mammals are streamlined.

A further development of the swimming limbs, the transformation of the entire hand and legs to fins dar. In these, the fingers and toes are connected not only by a thin skin, but fully integrated into a muscular paddle and no longer recognizable as individual rays. This type of transformation has been formed within the mammals only in the three groups of marine mammals as convergence: the seals, manatees and whales. Here are all these groups passed from country life to a more or less complete life in the sea water, only a few species within the whales and seals specialized in a further step on life in fresh water.

Within the marine mammals, the transformation of the extremities is least advanced in the seals, especially for locomotion on land is still possible. The front legs provide here is a fin in which the five digital rays are fully available. The first finger beam, however, this increases significantly and strongly developed, the length then decreases smoothly. The hind limb includes all five beams, here are the two outer significantly extended. The webbed feet, which go beyond the finger rays are supported by cartilaginous tissue. The locomotion and thus the use of fins is different for the two major groups of seals: While the eared seals use the front flippers as a driving organs and use the hind legs only to control and support, use the earless seals the pooled hindlimbs for propulsion and support this with the front legs.

In the manatees the front legs form a fully enclosed paddle, in which no more beams are visible from the outside. This paddle can be moved in the wrist in both the elbow as. The hind legs are no longer present, and the tail was replaced by a large oar, the Fluke. The latter is the main driving element at the very slow swimming behavior of the animals, the front flippers form rudder to control the water.

The most of the marine life adapted are the cetaceans. Even with them, the hind limbs are completely missing, and the front legs are transformed into large, paddle-shaped fins ( flippers ). Unlike the sea cows however the joints are not present up to the shoulder joint. While the outer fingers are strongly shortened, the middle finger II and III are very long and have a significantly increased number of finger bones, namely up to fourteen ( Hyperphalangie ). The tail forms at all whales a horizontal fluke, which is designed as two-piece and tail fin propels the animals. For stability in the water arrives at the whales added an extra fin, the dorsal fin. It is an unpaired structure in the center of the back, which is supported only by connective tissue and cartilage and is immobile.

Breathing

Mammals are Lungenatmer, which means that they need the oxygen for respiration. No mammal is able to breathe in the water, since no gills exist. For this reason, all mammals that live in the sea, periodically to breathe to the water surface. But most of all the whales are able to very long to dive without the need for new oxygen. This is possible due to some physiological processes and changes in the lungs and other organs.

The nostrils of the whale lying on top of the head, making a full appearance for respiration is not necessary. With each breath, the animals change completely between 80 and 90 percent of lung contents of ( in land mammals, this share is only about 10 to 15 percent). The lung has a dual network of capillaries, which is otherwise found only in the manatees and the platypus, and allows to forbid double the amount of oxygen from the air we breathe. In comparison to the land mammals only a very small portion is of 9 percent of total oxygen stored in the lung, the major part of about 82 percent bound myoglobin in the muscle, and the rest is circulated in the blood. For comparison, the lungs of land mammals contain about 34 percent of the oxygen and the muscle only 25 percent. Thus, the oxygen also can be effectively transported, the whales have two to three times the relative amount of blood per kilogram of body weight as land mammals. When diving, the oxygen demand is also lowered, blood circulation and heart function slow down. In addition, some organs and body regions are decoupled from the bloodstream. The specific adjustments allow the whales, sometimes very long to stay underwater. So dive some rorquals up to 40 minutes, sperm whales up to 90 minutes and bottlenose whales even up to two hours. Sperm whales can thereby reach depths of over 3,000 meters.

The seals are mainly modifications of the circulatory system that allow longer dives. The blood flow is ensured despite reduced heart rate while diving, especially through flexible artery walls and cavities. The nose and the larynx are closed during the dive, as well as the circulation of the body is also reduced with them. A significantly higher amount of blood than land mammals, and an increased proportion of the blood pigment hemoglobin also allow a significantly higher oxygen uptake from the air. In particular, the Weddell seal and the southern elephant can thereby dive up to an hour and can reach depths of up to 66 meters.

Manatees breathe every two to five minutes and reach maximum dive times of about 20 minutes. As the whales they can be very effectively absorb oxygen via a double capillary network, and the metabolism is very slow with them. The heart rate is markedly lower than in animals of similar size and may be further lowered.

Thermoregulatory

Especially for mammals as homoiotherme, ie " warm-blooded " animals results in sea water the problem is that an effective thermal insulation must exist. The coat that handles this function in the country mammals, marine mammals have except some seals not because it is more of a hindrance in the water. Instead, all marine mammals have developed a very thick layer of fat that lies beneath the skin. This subcutaneous fat insulates the animals to the cold sea water and ensures that the body can maintain an even temperature. Some whales can this layer, referred to them as Blubber, thick up to 70 centimeters.

Particularly in the fur -free seal, the body surface is kept by a reduced blood flow in the region of the freezing point so as not to lose heat, in addition to the water. In contrast, the coat of fur seals has air inclusions which act as insulation to the outside.

The situation is similar with the sea otters who does not have the only marine mammal through an insulating layer of fat. Here, the heat insulation is concerned solely through an extremely dense fur with air pockets. Sea otters have up to 100,000 hairs per square centimeter fur.

Salinity

Due to the high salt content in seawater need to marine organisms, which have a significantly lower salt concentration in their body fluids to be able to eliminate the excess salt. They may not be given too much water. For mammals, this means that their kidneys have to be able to form a highly concentrated urine. For this reason, the kidneys of seals are lobed and have about 150 to 300 kidney lobe ( Renculi ). The kidneys of whales have even a few thousand Renculi and exist as elongated bodies of the spine.

In an inverse approach to marine mammals (fresh - ) can gain water from sea water. For although (fresh ) water is constantly lost by osmosis through the skin and with food mitgeschlucktes sea water has a high salt concentration, create these animals to maintain a much lower salt content in the body. It is characteristic of biological life, the order of the body to maintain against the " self ," the processes of inanimate nature, the entropy - leave in larger systems successively increase - the clutter.

Fish of the sea have the same ability to fish in fresh water the opposite task.

Nutrition

The food in the sea can be based on different bases. As with the land mammals also exist in marine mammals herbivores and carnivores. The Manatees are herbivores whose diet of seaweed and filamentous algae is that they graze. You have for this purpose large molars for grinding food.

Most seals and toothed whales hunt for fish and other marine animals that they can catch with their mouths. To this end, representatives of both groups possess uniform pointed teeth, which are necessary to hold the prey and in some species of toothed whales form a fish trap. Other toothed whales such as the beaked whales and various dolphins are specialized in the hunt for cephalopods, especially squid. They have a reduced number of teeth with great teeth, with which they can hold the prey.

Most modified are the whales that feed on krill cancers. These crabs live in large schools and are the basis of life for the baleen whales dar. The baleen whales, including the largest living animals in the world belong, was formed for the capture of crabs a pot of baleen plates that replace the teeth. The whales take their prey transitions huge amounts of water and cancers in the mouth and filter the water masses when pressing out through the baleen, the crabs remain in the Bartensieb hang and can be swallowed.

Convergences

As already shown, it is in the adaptations to the marine life in mammals to convergent developments, they were all so implemented independently in the course of evolution. The four groups of marine mammals come from very different relationship fields within the mammals. So the seals developed within the predators as a sister group of bears. The closest relatives of manatees are found, however, with the elephants and hyraxes. The relationship of whales is not yet finally resolved, according to recent findings, they come from artiodactyls from the nearest extant relatives are probably the hippos.

Similar adaptations to the marine life can be observed in other, not to mammals belonging, land vertebrates. Thus, the penguins have, within birds as well as sea turtles and extinct marine reptiles such as ichthyosaurs, marine crocodiles, plesiosaurs and other also developed a streamlined shape and paddle-shaped fins in the course of their adaptation to life in the sea. These animals are or were on the oxygen in the atmospheric air dependent and had to have corresponding adjustments to allow for longer immersion times. In contrast, the thermoregulation plays a role that solve this by a corresponding sub plumage and a layer of fat only when the penguins; the reptiles adapt as cold-blooded animals to the environment and live or lived accordingly, especially in warmer marine areas.

Reasons for habitat modification

Possible reasons for the habitat change back from land to sea, the competition with other rural residents and / or the use of new resources can be viewed. So there may have been for the early forms of today's marine vertebrates a supply of food in the sea, they could use better than the fish (eg krill ). About the gradual adaptation and the training of key features such as the webbed, the altered body shape and other characteristics of these animals were able to penetrate further in the course of evolution into the sea than their competitors. In this way, special transition types, which are the ancestors of the present-day sea creatures were formed.