Juno

海牛是一種溫順、行動(dòng)緩慢的生物。據(jù)考證，海牛原是陸地上的“居民”，是大象的遠(yuǎn)親。

The manatee is a large marine 1）mammal. Manatees are also known as sea cowsdue to their slow， 2）lolling nature and their grassy meals. However， despite the name，they are more closely related to elephants. Manatees and elephants evolved from thesame ancestor over 50 million years ago.

There are three species of manatee， 3）distinguished primarily by where they live.The West Indian manatee ranges along the North American east coast from Floridato Brazil. The Amazonian manatee species inhabit the Amazon River and the Africanmanatee swims along the west coast and rivers of Africa. Manatees range in sizefrom 2.4 to 4 meters and can weigh 200 to 590 kilograms. Though they may seem like4）cumbersome creatures， manatees can swim quickly and gracefully. Manatees usuallyswim about 8 km/h， but they can swim up to 24 km/h in short bursts when they feel aneed for speed.

Like whales and dolphins， manatees breathe air. Theygo to the surface for a gulp of air every three to five minutes.However， they can hold their breath underwaterfor up to 20 minutes. This may have to do withthe size of their lungs， as they run much of thelength of the manatee's body.

Manatees have been under attack by humansfor a long time， threatened by fishing nets， boat5）collisions， and 6）coastal development. TheIUCN's Red List of Threatened Species lists allmanatees as vulnerable or endangered and facinga high risk of extinction.

海牛是一種大型海洋哺乳動(dòng)物。海牛由于行動(dòng)緩慢、懶洋洋的天性和以海草為主的饑食，也被稱為海里的牛。然而，盡管它們名字與牛有關(guān)，但其實(shí)它們與大象的關(guān)系更為密切。海牛和大象是從5000多萬(wàn)年前的同一祖先進(jìn)化而來(lái)的。

海牛有三種，主要以它們居住的地方為界。西印度海牛分布在佛羅里達(dá)州到巴西的北美東海岸。亞馬遜海牛棲息在亞馬遜河中，非洲海牛棲息于西海岸和非洲河流。海牛體型長(zhǎng)達(dá)2.4～4米，體重達(dá)200～590千克。雖然海?？雌饋?lái)很笨重，但它們可以快速而優(yōu)雅地游泳。海牛通常以每小時(shí)8千米的速度游泳，但當(dāng)它們感到需要速度時(shí)，它們可以在短時(shí)間內(nèi)游到每小時(shí)24千米。

像鯨魚和海豚一樣，海牛也呼吸空氣。它們每三到五分鐘浮出水面吸一口空氣。然而，它們可以在水下屏住呼吸長(zhǎng)達(dá)20分鐘。這可能與它們的肺的大小有關(guān)，肺占海牛身體的大部分。

海牛長(zhǎng)期受到人類的捕殺，受到漁網(wǎng)、船只碰撞和海岸開(kāi)發(fā)的威脅。世界自然保護(hù)聯(lián)盟將所有海牛列為脆弱或?yàn)l危物種，它們面臨滅絕的高風(fēng)險(xiǎn)。