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RETURN TO THE SEA  ~50 million years

The cetaceans (whales, dolphins and porpoises) are descendants of land-living mammals. Their terrestrial origins are specifically indicated by:

-Their need to breathe air from the surface ;

-The bones of their fins, which resemble the jointed hands of land mammals;

-The vertical movement of their spines, characteristic more of a running mammal than of the horizontal movement of fish.

The question of how land animals evolved into ocean-going leviathans had been a mystery for a long time, owing to gaps in the fossil record. However, recent discoveries in Pakistan have clarified many of these questions, and revealed several stages in the transition of the cetaceans from land to sea.(click to see all the article on Wikipedia)

重返海洋 ~5千萬年前









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