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Evolution — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYEvolution4 Marks
Question
Give a brief account of evolution of vertebrates.
✓

Answer

→ About 2000 million years ago the first cellular life was found on earth.
→ About 350 million years ago, jawless fishes emerged.
→ Fish caught in South Africa in 1938, believed to be coelacanth, were thought to be extinct. → These animals evolved into known as lobefins, the first amphibians that could live on both land and water.
→ Although none of these specimens have survived to us, they were the ancestors of today's frogs and salamanders.
→ Reptiles descended from amphibians.They laid thick shelled eggs which did not dry out like amphibian eggs.
→ At the present time once again we can only see their descendants, tortoise, kashyapa and crocodile.
→ 200 million years or during which reptiles of different shapes and sizes dominated the earth.
→ Probably 200 million years ago evolved into reptiles like mastya and returned from land to water.
→ The land-dwelling reptiles were definitely dinosaurs.
→ The largest reptile Tyrannosaurus rex (T-rex) was 20 feet tall and had huge fearsome spear- like teeth.
→ About 65 million years ago, dinosaurs suddenly disappeared from the earth, which some believe to have been wiped out due to climatic changes.
→ Some even say that most of them may have evolved into birds.
→ But the truth is somewhere between these two. Because the small size reptiles of that time still exist.
→ Earlier mammals were like shrews.
Mammals were very intelligent in terms of sensitivity and overcoming fear.
→ When the reptiles decreased, the mammals took over the earth.
→ Mammals like horses, hippopotamus, bears, rabbits etc. were seen in South America.
→ Due to the continental drift, when North America joined South America, the animals of North America were scattered.
→ Due to similar continental drift, marsupials
survived in Australia because they did not have to compete with other mammals.
→ Some mammals live entirely in water. Whales, dolphins, seals and sea cows are some examples.

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