Manatees are large, fully aquatic marine mammals that are sometimes referred to as sea cows.

Manatees（海牛）是大型的完全水生哺乳动物，有时也被称为 sea cows。

Like other aquatic mammals, such as dolphins and porpoises, this wolf-sized animal, known as Pakicetus, is part of the cetacean group.

像其他水生哺乳动物，如海豚和鼠海豚一样，这种体型像狼一样大小的动物被称为巴基斯坦古鲸，是鲸类的一员。

Back in the 1970s, officials in Florida counted just a few hundred of these aquatic mammals.

早在 20 世纪 70 年代，佛罗里达州的官员就统计了这种水生哺乳动物的数量。

The bone -- called an involucrum-- helps aquatic mammals hear underwater, and it shows up even in the earliest cetaceans.

这种骨头——称为外包壳——有助于水生哺乳动物在水下听到声音，它甚至出现在最早的鲸类动物身上。

Their “sublimely secretive” nature makes them a muse to poets and a mystery to scientists, who still have much to learn about these aquatic mammals.

“无比神秘”的它们是诗人的灵感之源，也是科学家眼里的谜团，关于这些水族哺乳动物，还有很多东西等着他们去学习。

For land mammals, oxygen is plentiful in the environment, But because aquatic mammals can't breathe water, they have to hold their breath.

对于陆地哺乳动物来说，环境中的氧气是充足的，但由于水生哺乳动物无法在水中呼吸，它们不得不屏住呼吸。

Manatees are aquatic mammals, which means that although they never leave the water where they live, they must come to the surface every few minutes to breathe air.

海牛是水生哺乳动物，这意味着它们虽然从未离开过它们生活的水域，但必须每隔几分钟浮出水面呼吸空气。

Unlike other aquatic mammals like seals and walruses, manatees do not have blubber to protect them from cold temperatures, which means that they can only survive in warm waters.

与海豹及海象等其他水生哺乳动物不同，海牛没有鲸脂可抵御低温，这意味着它们只能在温暖的水域中存活。

These special species are called marine mammals, whales, dolphins, seals, porpoises, manatees, sea otters, polar bears and a few other aquatic mammals that rely on the ocean to survive but also need to breathe air.

这些特殊的物种被称为海洋哺乳动物，鲸鱼、海豚、海豹、鼠海豚、海牛、海獭、北极熊和其他一些水生哺乳动物，它们依靠海洋生存，但也需要呼吸空气。