Antarctic bears and polar bears

The Antarctic and the Arctic are the coldest places on the earth, where the cold wind howls, the temperature is very low, and it is covered with snow and ice all year round. It is a silvery white world. But in fact, the South Pole is colder than the North Pole, and there are more glaciers. Because the Antarctic region is a continent, the heat storage capacity is weak, and the heat gained in summer is quickly radiated. Therefore, the average annual temperature in Antarctica is only -56℃. In the ocean around the Antarctic continent, there are a lot of ice floating, forming a huge iceberg.

In contrast, the land area of the Arctic region is small, and most of it is the Arctic Ocean. Because of the large heat capacity of seawater, it can absorb more heat and dissipate heat slowly, so the annual average temperature there is about 8℃ higher than that in Antarctica. Therefore, there are fewer glaciers in the Arctic than in the Antarctic, and most of them are piled up in Greenland.

According to the investigation, the average thickness of Antarctic ice sheet is1700m, the thickest part can reach 4000m, and the total volume of glaciers is about 28 million cubic kilometers. The thickness of the Arctic ice is about 2-4 meters, and the total volume of glaciers is only one tenth of that of the South Pole.

Why are there no bears in Antarctica? - -

The South Pole and the North Pole are the highest latitudes on the earth and the coldest regions on the earth. But there are different animals in the Antarctic and the Arctic. There are formidable fierce polar bears in the Arctic; There are a large number of penguin families in Antarctica, and the largest mammal in the world swims in the waters near Antarctica? d？ D blue whale. However, careful readers will find that there are no penguins in the Arctic; And the Antarctic continent does not have the largest surviving terrestrial carnivore common in the Arctic? d？ D polar bear. Why is this?

This problem is closely related to the origin and evolution of bears, zoogeography, geology, glaciology and ecology. Tracing back to the origin of bears, the ancestors of modern bears were 2400 years ago? d？ Late Miocene bears, D500 and 5 million years ago? Yao Yao Although bears appeared late on the earth, they developed rapidly 500 years ago. The Pliocene and Pleistocene in D 1 10000 were very prosperous, and their footprints were almost all over the world (except Antarctica).

The geographical distribution of animals is also closely related to the history of geological development. The physical and geographical environments of the North and South poles are obviously different. The Arctic is an ocean basin surrounded by the mainland, an ocean between Eurasia and North America? North Henan? Foreign? ┲ line copy 1 rush? Terrestrial mammals and marine mammals are closely related to the surrounding terrestrial and marine life in biological history, forming a fauna distributed around the Arctic.

Antarctica is completely different. Antarctica is a continent surrounded by the Pacific Ocean, Indian Ocean and Atlantic Ocean. 300 million years ago, at the end of Carboniferous and the beginning of Permian, the whole land mass of the earth was once combined into two unified ancient lands. At the end of Paleozoic, about 250 million years ago, the unified ancient land began to split. Up to now, 60 million years ago, Antarctica was completely separated from the surrounding continents and became an independent continent.

Bears are omnivorous and adaptable terrestrial animals, distributed from the Arctic to the tropics. In Tertiary, due to the cold climate of the earth, glaciers formed in the north and south poles. Warm-loving animals that had no time to migrate from polar regions to warm regions were extinct, and only some animals adapted to cold climate lived on the edge of glaciers. The cave bear, which used to feed on arctic plants, disappeared, but a bear with thick fur, much meat, temperature regulation ability and wintering physiology and biochemistry adapted to the cold survived in the Arctic. This is the future polar bear. They become strict carnivores by feeding on the carrion of seals, walruses, fish, eggs and stranded whales.

On the other hand, long before the ancestors of bears appeared, Antarctica was a continent surrounded by oceans and was not connected with other continents. The division of the ocean makes it impossible for bears on land to migrate there, so it is impossible to find polar bears in Antarctica. On this continent with an area of 6.5438+0.4 million square kilometers, there are no animals of continental flora, and all animals belong to marine fauna.

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The snow-covered Antarctic is the main habitat of penguins. In addition to Antarctica, penguins are also distributed on many islands in the southern hemisphere, even on the Galapagos Islands near the equator. However, it is quite puzzling that penguins can't be seen in the Arctic region with the same cold climate and vast ice and snow.

The hot weather prevented the penguins from going north.

Some scientists believe that this has to start with their ancestors. The ancestors of penguins are tube-nosed animals, which developed from the south of the equator. Penguins not only decide the direction of development, but also decide where their main home is. Zoologists speculate that they only chose to go south at that time and did not continue to advance north. Because the tropical hot climate blocked their way northward, especially they couldn't stand the warm tropical water. The physiological characteristics of penguins determine that they must stay in the waters where Antarctic ice and snow melt, or in the waters where deep-sea cold water flows. In this way, the warm equatorial airflow and high temperature form a physical barrier, which prevents penguins who are afraid of heat from swimming. Looking back at the distribution of penguins, the northernmost limit of their distribution is the area with an annual average temperature of 20 degrees, which is quite consistent with the speculation of zoologists.

Human greed wiped out innocent penguins.

However, Kauzhan once found an extinct bird skeleton in the Arctic, which is very similar to a penguin. Researchers call it the "big penguin". This giant penguin is about 60 centimeters tall, which is about the same size as the most abundant Adelie penguin in Antarctica. Their heads are brown, their feathers are black and their bellies are white. The skeletal structure of big penguins shows that they also have a clumsy and swaying way of walking, and they are also good at swimming in the sea, which is almost the same as modern penguins. Scandinavia in Europe, the coastal areas of Canada and northern Russia, and all the islands in the North and South Poles are the main distribution areas of giant penguins, which once numbered millions. However, they feed in the ocean and breed on land, and are threatened by both marine and land predators, so their defense ability is poor, which makes them suffer a disastrous defeat in the survival competition of mammals developed in the same period and be swallowed in large quantities; The surviving penguins are also limited to coastal or isolated islands that are less affected by predators. However, humans deprived them of their last chance to survive in the northern hemisphere.

When early humans invaded the Arctic region, the calm life of the big penguin began to suffer some damage. By about 1000 years ago, the vikings also discovered this kind of big penguin. They also found that this animal is almost a treasure. To their delight, penguins have no resistance to humans. So, humans began to kill big penguins. Three or four hundred years ago, there was an upsurge of exploring the Arctic in Europe. At the same time, driven by greed and desire, human beings hunt these innocent animals. Large penguins in Greenland, Queen Elizabeth Islands and other places were forced to have nowhere to live, and the number dropped sharply, which eventually led to the "genocide" of large penguins. 1On June 2nd, 844, the last two penguins in the northern hemisphere were arrested and killed on an island in Hainan, Ireland. Now, there are no penguins in the Arctic except the bones occasionally found for human beings to mourn.

At present, Antarctica has become an ideal home for penguins: the South Pacific Ocean current where cold and warm meet, the abundant food and nutrients in the sea provide superior conditions for penguins to survive, and the natural barrier formed by the ice and snow plateau prevents animals from migrating to the south, making penguins rarely attacked by predators here. For penguins, the biggest danger here is snowstorm. For penguins, Antarctica has become their safest place to live.

Arctic exploration destroyed the big penguin (Figure)

Penguins stand like people on land, always looking forward to something, so they are called penguins, and the original meaning of "enterprise" in Chinese is to stand on tiptoe. Penguin is special in that it has a bird's head and beak, but it can't fly and can only stumble on land. This is the most doubtful question, whether it should belong to birds. Except penguins, only ostriches can't fly, but ostriches run very fast, so people have no doubt about their bird identity.

When the Portuguese explorer Magellan led the global expedition to the coast of South America, the team members found a "strange goose" that they had never seen before. These strange geese have a particularly dull expression when they are motionless, and the members of their own expedition are very similar to those "geese" in their dull expressions. The lonely explorers shouted Pigafetta's name as soon as they saw the strange goose. Pigafetta's approximate sound "Penguin" became the name of penguin in a joke and spread.

In order to find out the trace and distribution of penguin ancestors, biologists have spent great energy. The results of paleontological research show that penguins appeared in Tertiary as early as 50 million years ago, and it was found that penguins once lived in the Arctic, because an extinct bird skeleton was found in the Arctic, which was called "Big Penguin".

This "big penguin" is about 60 cm tall, with a brown head, black feathers on the back and a white abdomen. They are as clumsy as other penguins when walking on land, but they are also good at swimming in the sea. "Big Penguins" are mainly distributed in Europe, Scandinavia, Asia and North America, and some islands in the Arctic Ocean, with a number of one million. However, three or four hundred years ago, Europe set off an upsurge of exploring the Arctic. With the arrival of explorers and immigrants, the "big penguin" has become the object of contention, and its number has dropped sharply. When the last "big penguin" was killed, there were no penguins in the northern hemisphere. This is why there are no penguins in the Arctic.