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New research by scientists at the University of Bristol explains how a 'stop-start' pattern of evolution, governed by environmental change, could explain why crocodiles have changed so little since the age of the dinosaurs.
鱷魚自恐龍時代以來幾乎沒有變化，布裡斯託大學（英國）的科學家們進行的一項新研究從環境變化影響下的「走走停停」的進化模式解釋了這一現象的原因。
Crocodiles today look very similar to ones from the Jurassic period some 200 million years ago. There are also very few species alive today -- just 25. Other animals such as lizards and birds have achieved a diversity of many thousands of species in the same amount of time or less.
如今的鱷魚和兩億年前的侏羅紀時代的鱷魚長得很像，現存種類非常少--僅有25種，但在相同或更短的時間跨度裡，其他物種，例如蜥蜴和鳥類已經衍生了多達數千種類。
Prehistory also saw types of crocodile we don't see today, including giants as big as dinosaurs, plant-eaters, fast runners and serpentine forms that lived in the sea.
史前也曾出現過不同於今日的鱷魚種類，包括像恐龍一樣大小的巨型鱷魚，食草鱷魚，移動速度極快的鱷魚以及生活在海洋裡的蛇形鱷魚。
In the new research, published today in the journal Nature Communications Biology, the scientists explain how crocodiles follow a pattern of evolution known as 'punctuated equilibrium'.
這項新的研究發表於今天出版的《自然通訊生物》雜誌上，研究組科學家在文中解釋了鱷魚如何遵循一種名為「間斷平衡」的進化模式。
The rate of their evolution is generally slow, but occasionally they evolve more quickly because the environment has changed. In particular, this new research suggests that their evolution speeds up when the climate is warmer, and that their body size increases.
鱷魚的進化速度通常很慢，但是偶然情況下因為周圍環境變化他們的進化會變快。這項新的研究指出，尤其是當氣候變暖時，他們的進化速度會變快，體型也會增大。
Lead author Dr Max Stockdale from the University of Bristol's School of Geographical Sciences, said: "Our analysis used a machine learning algorithm to estimate rates of evolution. Evolutionary rate is the amount of change that has taken place over a given amount of time, which we can work out by comparing measurements from fossils and taking into account how old they are.
這項研究的主要作者，來自布里斯托大學地理科學學院的馬克斯·斯託克代爾博士說:「我們的分析使用了一種機器學習的算法來預估進化的速率。進化速率指的是在一個指定的時間跨度裡的變化量，我們可以通過比較化石的大小以及考慮它們的年齡來計算得出。」
"For our study we measured body size, which is important because it interacts with how fast animals grow, how much food they need, how big their populations are and how likely they are to become extinct."
「在研究中，我們測量了物種體型的大小，這一數據很重要，因為它關乎動物生長的速度、飲食量的大小、物種群體的數量以及他們滅絕的可能性。」
The findings show that the limited diversity of crocodiles and their apparent lack of evolution is a result of a slow evolutionary rate. It seems the crocodiles arrived at a body plan that was very efficient and versatile enough that they didn't need to change it in order to survive.
研究結果表明，鱷魚物種多樣性的限制和明顯的進化停滯是低進化率的一個結果。就像是鱷魚的體型已經達到了一個非常高效、可適應所有變化的狀態，他們已經不需要再做更多改變以增加存活率。
This versatility could be one explanation why crocodiles survived the meteor impact at the end of the Cretaceous period, in which the dinosaurs perished. Crocodiles generally thrive better in warm conditions because they cannot control their body temperature and require warmth from the environment.
這一多適應性也解釋了為什麼白堊紀時代恐龍滅絕了，而鱷魚卻能夠在流星撞擊地球後還能存活下來的原因。鱷魚一般在溫暖的環境中生長得更好，因為他們不能控制自己的體溫，需要從外界環境中獲得溫暖。
The climate during the age of dinosaurs was warmer than it is today, and that may explain why there were many more varieties of crocodile than we see now. Being able to draw energy from the sun means they do not need to eat as much as a warm-blooded animal like a bird or a mammal.
恐龍時代的氣候比現在更加溫暖，這也許說明了為什麼那個時候的鱷魚種類要比現在多。鱷魚可以從太陽光中獲取能量，這一技能也意味著他們不用像鳥類或者哺乳動物這樣的恆溫動物吃那麼多。
Dr Stockdale added: "It is fascinating to see how intricate a relationship exists between the earth and the living things we share it with. The crocodiles landed upon a lifestyle that was versatile enough to adapt to the enormous environmental changes that have taken place since the dinosaurs were around."
斯託克代爾博士補充說:「看到地球和與我們共享地球的生物之間存在著多麼複雜的關係，真是令人著迷。鱷魚選擇了一種可多樣適用的生活方式，足以適應自恐龍時代以來發生的巨大環境變化。」
The next step for the team's research is to find out why some types of prehistoric crocodile died out, while others didn't.
研究小組的下一步將研究部分史前鱷魚滅絕，而另一些卻存活的原因。
Story Source:
Materials provided by University of Bristol. Note: Content may be edited for style and length.
Jurassic period 侏羅紀時代
prehistory 史前時代
serpentine蛇形的，蛇形之物
algorithm 算法
versatile 多才多藝的，通用的，萬能的
warm-blooded 恆溫的，熱血的