【经济学人】巴西发现了新化石？丨2016.11.12丨总第742期

My, what sharp teeth you have

天，好锋利的牙齿！

HOW the dinosaurs died out after ruling the planet for over 150m years was a mystery that consumed palaeontologists throughout much of the 20th century. These days it is mostly accepted that they were done in by the climatic after-effects of the impact of a giant asteroid, specifically the one that carved a vast crater 180km across near the Yucatan Peninsula in Mexico. Now the focus has shifted from how they died out to where they came from in the first place. In a paper just published in Current Biology, a team led by Max Langer at the University of São Paulo reports the excavation of four fossils that shed some intriguing light on two different aspects of that question.

称霸这个星球一亿五千多年的恐龙是如何灭绝的？这个谜题困扰了古生物学家大半个20世纪。近来大家普遍接受的观点是:巨大小行星撞击地球造成气候变化进而致使恐龙灭绝，尤其是在墨西哥尤卡坦半岛附近发现的一个直径达180km的巨大陨石坑（使人们更加相信这一说法）。而现在大家关注的焦点从恐龙灭绝转移到它们起初从何而来的问题上。据《当代生物学》最新刊载的论文，圣保罗大学Max Langer带领的团队刚发掘出四块化石。这四块化石从两个不同方面揭示了这一问题。

• Shed light on: 进一步揭示，阐释

The fossils, found by Sergio Cabreira at the Lutheran University of Brazil, come from the Santa Maria formation in the south of the country. One of them, at 230m years in age, is one of the oldest dinosaur fossils ever found. Typically, such ancient finds are nothing more than bone fragments, but this specimen, named Buriolestes schultzi, is in remarkably good shape. It is a distant ancestor of the long-necked sauropods such as Diplodocus and Brachiosaurus. Those giant animals, which stood up to 16 metres high and weighed 50 tonnes or more, were vegetarians.

巴西路德大学的Sergio Cabreira在巴西南部的圣玛利亚地层发现了一些化石。其中一块化石距今已有两亿三千万年，是迄今为止最古老的化石。通常这类化石无非是骨头碎片，但Buriolestes schultzi标本，却相当完好。这是一个长颈蜥脚类恐龙，如梁龙或蜿龙的远祖。梁龙或蜿龙这类巨大生物高达16米，重达50吨以上，并且都是食草动物。

B. schultzi seems to have been both diminutive —about 1.5 metres long—and carnivorous. Its teeth are curved and have serrated edges, traits usually associated with meat-eating. That finding raises as many questions as it answers: palaeontologists must now ponder when and why sauropods made the switch from eating meat to eating plants. Size probably had something to do with it: it is difficult to see how an animal the size of Brachiosaurus could have hunted enough prey to support its enormous bulk. But were B. schultzi’s descendants forced to become herbivorous as they grew? Or did they switch to a vegetable diet first, then take advantage of the opportunities for growth that offered?

由B. schultzi标本看出，这是一种小型（大约有1.5米长）食肉动物。它们的牙齿呈弧状，且带有锯齿形边缘，这些通常是肉食动物的特征。这一发现阐释之前存在的一些问题，不过也引发了其他问题。古生物学家现在需要思考：爬行类动物何时又为何会由吃肉变成了吃草？体型大小可能和这一问题有关：Brachiosaurus的体型巨大应该很难捕到足够的猎物。难道B.schultzi后代是在生存的过程中被迫变了食草动物？又或是它们很早就从食肉动物转化为食草动物了，之后借助自然界提供的这一优势，体型不断变大？

• diminutive:小的

• take advantage of：利用

The other fossils in the find address a different question. Palaeontologists have long thought that dinosaurs rose to dominance at the dawn of the Jurassic period, 201m years ago, by out-competing and rapidly replacing other land animals that emerged earlier. One such group was the lagerpetids, a group of reptiles with some dinosaurian characteristics that arose about 236m years ago, during the Triassic period.

此次发掘的其他化石也解决了另一个问题，古生物学家过去一直认为恐龙是在两亿一百万年前的侏罗纪早期，通过打败和取代其他早期陆地动物称霸地球的。比如，恐龙取代了大约两亿三千六百万年前三叠纪时期lagerpetids群体(一些带有恐龙特征的爬行动物）。