导读】
距今约2.5亿年~6500万年的中生代，分为三叠纪（Triassic）、侏罗纪（Jurassic）和白垩纪（Cretaceous），是地球物种丰富的时期。恐龙统治了侏罗纪和白垩纪，但是在漫长的生命史上昙花一现，而与恐龙同时代的鳄鱼却延续到了今天，上演了一场古生物版的龟兔赛跑。伯克利大学的Sarah Werning与同事通过查找化石发现，原来恐龙与鳄鱼有着共同的祖先，因进化方向不同，形成了生长迅速的恐龙和生长缓慢的鳄类，而这种不同的生长方式决定了他们在物种大灭绝的撞击灾难中的命运。 【译文】 Palaeontology 古生物学
The hare and the tortoise 古生物版龟兔赛跑
Or, rather, the dinosaur and the crocodile 恐龙和鳄鱼
Dec 3rd 2011 | from the print edition
FASHION affects all human activities, and science is not exempt. In the field of palaeontology, for example, the stock of crocodiles is rising. Their role in Mesozoic[1] ecosystems, including as predators of dinosaurs, has been reassessed over the past few years—and their diversity of forms (even including herbivorous species) is becoming increasingly apparent. This shift of perception is causing fossil hunters to take a renewed look at crocodiles, dinosaurs and the similarities and differences between them. 所有的人类活动都受到时尚的影响，当然科学也不例外。例如在古生物学领域中鳄类数量在增多。过去几年中，重新评估了像恐龙、鳄鱼这样的食肉动物在中生代的生态系统中地位，发现它们的种类多样性（甚至包括食草种类）在明显增加。之所以有这种认知上的改变，是因为化石搜集者重新观察了鳄鱼、恐龙化石之间的相同点和不同点。
One such study, conducted by Sarah Werning of the University of California, Berkeley, and her colleagues, is reminiscent[2] of Aesop’s fable about the hare and the tortoise—with dinosaurs playing the role of the cocky[3] lagomorph[4] and crocodiles that of the slow but steady chelonian[5]. One of the traits which allowed dinosaurs to dominate the fauna of the Jurassic and Cretaceous periods was that they grew rapidly.
This is clear from their bones, which show four traits associated in living animals with fast growth: that they have numerous canals through which blood vessels would have passed for the transport of nutrients; that those canals are arranged in complex networks, rather than running separately through the bone; that fibres of collagen (a protein which helps make bone supple) are loosely organised within them, rather than being tightly packed; and that they have large clusters of cells called osteocytes[6], which are important in the formation and maintenance of bone. In these characteristics, dinosaur bones are similar to those both of mammals and of dinosaurs’ modern descendants, the birds, and dissimilar to those of both ancient and modern crocodiles.
加州伯克利大学的Sarah Werning和她的同事进行了这种研究。一切很像伊索寓言中的龟兔赛跑，恐龙相当于故事中狂妄自大的兔子，鳄鱼则扮演慢而坚定的乌龟。生长迅速这一特点，是恐龙能过统治侏罗纪和白垩纪的原因之一。这点从化石中清晰可见，联系现今物种，骨骼生长迅速有四个特点：大量的通道，这样血液能够运送更多的营养成分；在骨骼中它们并不是分散存在，而是形成网络；它们之间有松散的胶原蛋白（一种使骨骼柔软的蛋白质）纤维，而不是紧紧的绑在一起；存在大量形成和维持骨骼的骨细胞。有了这些特点，恐龙的骨骼和哺乳动物就很相似，也和它们的后代——鸟类相似，但这些与古代和现代的鳄鱼不相同。
Dinosaurs are not unique in showing signs of rapid growth, though. Pterosaur bones have similar features, as do those of several other groups of Mesozoic reptiles. Ms Werning therefore decided to trace the phenomenon of rapid growth back as far as she could in the fossil record, by examining the bones of a wide variety of species.
恐龙并不是唯一生长迅速的物种。食肉动物的骨骼特征和一些中生代爬行动物也有相似之处。因此，Werning女士尽可能地检查很多物种的骨骼，追踪生长迅速的化石记录。
The upshot, she discovered, was that the features indicating rapid growth were added one by one during the Triassic (the period immediately before the Jurassic). That is not terribly surprising. What is surprising is that all of these features were present in the last common ancestor of dinosaurs and crocodiles. The former, in other words, perfected rapid growth and went on to dominate the Mesozoic, while the latter gave it up.
经过检查，一点点的追溯，结果发现三叠纪（侏罗纪之前的一段时期）是生在迅速的阶段。这还不是最让人惊讶的，让人真正惊讶的是恐龙和鳄鱼的共同祖先具有这些特点。前者完美地进化成生在迅速的恐龙，并统治了中生代，后者则放弃了。
Crocodiles had the last laugh, though. Fast-living dinosaurs were unable to survive the crisis at the end of the Cretaceous, when an asteroid hit Earth and brought photosynthesis to a halt. Slow-living crocs, by contrast, were able to cling on until conditions improved, and are now found throughout the tropics and subtropics. Thus, 65m years ago, were the fates of two groups of animals decided by evolutionary differences inculcated 220m years ago. Aesop would have been proud.
然而，鳄鱼笑到了最后。生在迅速的恐龙没有渡过中生代的危机——小行星撞击地球，撞击产生的尘埃阻碍了光合作用，但是生长缓慢的鳄鱼可以坚持到环境好转，并且现在常见于热带和亚热带。因此，六千五百万年前，恐龙和鳄鱼的命运是由两亿两千年进化产生的不同之处决定的。那么伊索寓言就因此得证了。 【生词】
[1] Mesozoic [?mes?u?z?uik] n./adj.中生代（的）
[2] reminiscent [?remi?nisnt]adj. 提醒的，暗示的；像…似的；回忆过去的
[3] cocky [?k?ki:]adj.狂妄自信的
[4] lagomorph [?læɡ?m?:f]n.兔类动物