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Science and Technology
科學技術
Palaeontology
古生物學
Splay-footed, not flat-footed
八字足，而非平足
A new fossil shows that evolution does not always mean change
一個新的化石表明：進化并不總是意味著改變
Then and now
過去與現在
WHEN a coelacanth, a type of lobe-finned fish once considered the missing link between fish and amphibians, was found off the coast of South Africa in 1938, it came as a shock to palaeontologists.
以前人們一度認為一種叫做腔棘魚的鰭魚是魚類和兩棲類之間缺少的環節，1938年當腔棘魚在南非海岸沿海被發現時，古生物學家對它的出現大感震驚。
Until then, the most recent traces of such a creature had been in rocks dating from the last days of the dinosaurs, 65m years ago.
在此之前，這種動物最近的遺跡出現在6500萬年前恐龍時代后期的巖層中。
It was, in its way, as surprising as if a live Tyrannosaurus had been found hiding in an obscure part of Montana.
而它這次的出現方式，就好像一個活生生的霸王龍屬被發現藏身在蒙大拿州的模糊地帶一樣令人驚訝。
Now the same experience is hitting palaeontologists again—but this time in reverse. Instead of finding a living fossil identical to an ancient beast, they have found a real fossil identical to a modern one.
現在，同樣的經歷再次讓古生物學家碰上了，不過這次相反。他們不是找到了一個與古獸相同的活化石”，而是找到了一個跟現代獸類相同的真正化石。
The fossil in question, a 100m-year-old specimen from north-east Brazil, belongs to the genus Schizodactylus.
所討論的的化石采自巴西東北部，是一億年前的標本，屬于節肢動物類。
These are large, carnivorous, cricket-like insects whose feet splay out wildly in different directions.
這類節肢動物是大型類似板球的食肉昆蟲，其足向不同方向伸展開來。
Modern Schizodactylus use their feet like snowshoes, to help them remain stable as they travel over sandy terrain in search of prey.
現代節肢動物在沙地爬行尋找獵物時用它們雪鞋般的腳來幫助身體保持穩定。
If the new fossil—whose discovery has just been published in ZooKeys by Sam Heads of the Illinois Natural History Survey and Léa Leuzinger of the University of Fribourg, in Switzerland—were merely similar to modern splay-footed insects, the find would not be particularly surprising:
如果新化石其發現剛由伊利諾斯州自然史調查的負責人山姆和瑞士弗里堡大學的李?勞伊辛格發表在《動物圖譜》上僅是類似現代的八字足昆蟲，那么這個發現不會特別令人驚訝：
it simply demonstrates a phenomenon called evolutionary stasis, in which a specific type of body form hangs around for a long time.
它只是證明了一種被稱為進化停滯的現象，在這種現象中特定類型的體型存留很長一段時間了。
What is surprising is just how static Schizodactylus has been.
令人驚訝的是節肢動物停止進化竟有這么久了。
Evolutionary stasis is fairly common at the higher levels of the Linnaean system of biological classification.
在林耐生物分類系統的高等類別中進化停滯現象是相當普遍的。
Natural selection hits on a good design.
自然選擇的圖案都是最好的。
That design is then adopted in slightly different forms by species after species.
然后，這種圖案就被一個接一個的物種以略有不同的形式所采納。
The shelled bodies of turtles, for example, evolved between 250m and 200m years ago, while the body plans of scorpions have been around for more than 400m years.
例如，海龜的殼體是在2.5～2.0億年前進化的，而蝎子的體型方案已超過4億年的歷史。
That does not mean, however, that a zoologist would mistake a 200m-year-old turtle or a 400m-year-old scorpion for any species now alive.
然而這并不意味著一個動物學家會弄錯2億歲的海龜或是4億歲的蝎子屬于現在存活的何種物種。
What is remarkable about the new find is that it is so similar to modern animals that it can be assigned to an existing genus—the lowest level of Linnaean classification above a species—rather than just to some higher taxonomic group.
新發現引人注目的是它與現代動物如此相似，以致它可以被列入現有生物分類種類，而不是只被列入某一更高等的分類組。
That is rare indeed.
這的確罕見。
Even the modern coelacanth, on closer examination, had to be put in a different genus from any known fossil.
經過仔細觀察，甚至就連現代腔棘魚都必須得歸類于不同于任何已知化石的種類。
Clearly the body plan of Schizodactylus is not merely good, but optimal, at least for the environment the animal lives in.
顯然，節肢動物的體型方案不僅是最好的，也是最佳的，至少對這種動物生活的環境而言是如此。
Alas for Schizodactylus, the sandy deserts it prefers have retreated from north-eastern Brazil and its optimality there has vanished.
唉，對節肢動物來說，它所喜愛的沙質沙漠已經從巴西東北部退卻，它在那里的最佳體態已經消失。
But its discovery shows better what this part of the world was like 100m years ago—and also illustrates an important point about evolution that is often forgotten in biologists' understandable focus on the development of novelty. The first rule of natural selection is: If it ain't broke, don't fix it.”
但它的發現恰好說明這部分的大千世界跟1億年前的樣子很象，也說明了進化論的一個重點，而這點在生物學家關注理解新穎性的發展時往往被遺忘了。自然選擇的第一條規則是：如果沒壞，就不要修理它。”
