大開眼界：科學家育成陸上行走的魚類

語音：美式發音

適合精聽語速：200詞/分鐘

關鍵詞：fish，land-walking，adapt

魚類的起源和進化在生物發展史上具有十分重要的意義。魚類的出現標志著無脊椎動物向脊椎動物進化的一個質的飛躍，其發展及演化提供了動物進化的譜系。在多種古代魚類當中，其中一種與脊椎動物進化歷程關系最密切的品種，便是古總鰭魚。它們生活在泥盆紀時代，距今約三億五千萬年，當時陸地面積擴大，有明顯的季節性變化及周期性干旱，這種魚類被迫另找水源，長期的陸地“劃行”使得適于水中游泳的鰭變成了適于陸地爬行的四肢。

魚石螈是已知最早的兩棲類動物，化石發現于格陵蘭泥盆紀晚期的地層中，是脊椎動物從水到陸過渡階段的代表。其脊椎構造比起總鰭魚類有所進步，肢體已是早期兩棲類的模樣，能初步支撐身體在陸地上活動。

Taking a fish out of water—it’s an expression that describes something that literally shouldn’t work.But for some scientists，it apparently has.

This is the Senegal 1）Bichir...and it’s walking.Researchers took the fish from a young age and forced them to live on land for eight months，in conditions that were humid enough that they could survive.

“讓魚兒離開水”這句話表示某事行不通。不過對于一些科學家來說，這卻是可以做到的。

這條是塞內加爾多鰭魚……而它正在爬行。研究人員將魚苗從幼體開始培育，在一個濕度足以讓它們存活的環境中強迫這種魚在陸地上生活了八個月。

The study found the fish—which were previously known to move on land only 2）incidentally—could adapt to walking on land.Basically，what the study wanted to look at was how 3）tetrapods—four-legged creatures—first pulled themselves out of the water and made that “Little Mermaid” switch from 4）aquatic animals to 5）terrestrial ones.

There are well-documented cases of fish—like the 6）mudskipper—walking on land and even climbing trees.But unlike the mudskipper the bichir has lungs，and crucially，as the study found，their movement on land is much closer to that of the earliest tetrapods.

Now that’s due to a number of factors，including the positioning of their fins on their body，but one of the really interesting things the study 7）charted was how the fishes’ bodies adapted to life on land.

Scientists looked at the 8）clavicle and a couple other bones that link the bichir’s head to its body.They found the clavicle and one of the other bones changed significantly in the land-walking fish，adapting to accommodate its new motions.

Those findings show the fish’s anatomical plasticity—its ability to change and adapt its body，a trait that would’ve been crucial for the first fish to walk on land.

The study has also raised some more profound philosophical questions，like “If a fish could walk，would it still be a fish？” Well，the scientists who conducted the study don’t really have an answer for that particular question，yet.

研究發現，這種早前所知僅在偶然情況才會爬上岸的魚可以適應陸上行走。這一研究的主要目的在于探討四足動物當初是怎樣離開水域并完成“小美人魚”的華麗轉變，從水生走向陸生的。

早有充分資料表明，有些像彈涂魚這樣的魚類可以在陸地爬行甚至能爬樹。但與彈涂魚不同的是，多鰭魚體內長有肺部。