行走的鲸鲸类包括海豚和豚，是回到海洋和江河生活的哺乳动物，就象中生代的爬行动物鱼龙一样，成了彻底适应水生环境的动物。它们发展成了流线型的身躯，四肢和尾巴成了划水的鳍，但是在呼吸、繁殖和哺乳上仍保留了哺乳动物的习性。在以前很长一段时间里，由于没有发现从... Walking whale whales, including dolphins and dolphins, are mammals that return to the oceans and river life, just as the Mesozoic reptiles, such as the dragon, have become fully adapted to the aquatic environment. They developed into streamlined bodies, with their limbs and tail becoming paddled fins, yet retaining their mammalian habit of breathing, breeding and breastfeeding. In the past a long time ago, because did not find from ...