经济学人77:加拿大出土最早动物足迹

 　　Science and Technology Palaeontology Do the locomotion 1

　　科技 古生物学 活动活动
　　The earliest animal tracks yet found have been unearthed 2 in Canada
　　在加拿大出土了迄今为止发现的最早动物足迹
　　ONE of the greatest mysteries of the history of life is the Cambrian explosion.
　　寒武纪的大爆炸是生命史中最大的谜团之一。
　　Prior to 560m years ago, animal fossils are rare.
　　5.6亿年以前的动物化石寥寥无几。
　　Then, in a geological eyeblink, they become common.
　　然而，只过了地质史上一瞬间的功夫，它们便多得不足为奇了。
　　Shelly creatures such as trilobites and brachiopods, of whose ancestors there is little sign in the rocks, are suddenly everywhere.
　　像三叶虫、腕足动物此般壳类动物的祖先没有在岩层中留下什么痕迹，但它们的遗迹却突然间比比皆是。
　　Biologists would dearly love to know what happened.
　　生物学家们迫不及待地想知道当时到底发生了什么。
　　Recent discoveries at the delightfully 3 named Mistaken Point, in Newfoundland, serve to lift the veil slightly.
　　纽芬兰岛上有个地方名字很有趣，叫“错误点”，正是最近在这里的一些发现轻轻掀起了这个神秘面纱的一角。
　　These findings are not of Precambrian animals themselves, but of their tracks. And these, paradoxically, may be more useful.
　　发现的并不是寒武纪前的动物本身，而是它们的足迹。而出人意料的是，这些足迹可能还更有用。
　　Alexander Liu of Oxford 4 University and his colleagues took an interest in Mistaken Point because it is a site known for so-called Ediacaran fossils, shell-less animals of unknown provenance 5 that slightly predate the Cambrian.
　　牛津大学的亚历山大?刘和他的同事们之所以对“错误点”产生兴趣，是因为它因埃迪卡拉动物化石而闻名，埃迪卡拉动物是存在于略早于寒武纪时期的缘起不明的无壳动物。
　　As Mr Liu and his team explored the rocks they came across more than 70 markings that looked like tracks—slight impressions in the sediment 6 with tiny ridges 7 sticking up along the sides.
　　在刘和他的团队对那里的岩石进行勘察的过程中，他们发现了70多个类似足迹的斑点——在沉淀物中的一些浅痕，其周边有轻微的突起。
　　These markings, they report in Geology, are up to 13mm wide and up to 17cm long.
　　据他们在《地质学》杂志中的报告，这些斑点宽不过13毫米，长不过17厘米。
　　What is most curious about these tracks is that the rock they are in is reckoned to have formed at least a kilometre below sea level.
　　更奇特的是，据估计，这些足迹所在的岩石是在海平面至少一千米以下形成的。
　　Fossil bodies might get into such rock by sinking to the sea floor.
　　化石体倒是可能会沉到海底而进入这块岩石。
　　Tracks, however, must have been made by something that was alive.
　　然而，只有活的东西才能留下足迹。
　　Precambrian animals must therefore have lived at such depths.
　　因此，前寒武纪的动物肯定曾经生活在这么深的地方。
　　The tracks also cast light on what the Ediacarans actually were.
　　这些足迹也使我们了解了埃迪卡拉动物到底是什么。
　　Some palaeontologists think them members of a phylum that is now extinct.
　　有的古生物学家认为它们属于已经绝迹的一门动物。
　　Others, though, believe they were Cnidarians, the group that includes modern sea anemones 8 and jellyfish.
　　而有的则认为它们是刺胞动物，这是包括现代的海葵和海蜇在内的一门动物。
　　Cnidarians grow from embryos 9 that have only two layers of cells.
　　刺胞动物是由只有两层细胞的晶胚发展而来的。
　　Most animals, including all the shelly Cambrian ones, grow from three-layered embryos.
　　而包括所有寒武纪壳类动物在内的大多数动物都是由三层细胞的晶胚发展而来。
　　The tracks found by Mr Liu look suspiciously like those left by modern sea anemones which, despite their sedentary appearance, do move around slowly.
　　刘发现的这些足迹疑似现代的海葵的足迹。海葵虽然看起来不怎么活动，但它们确实会慢慢地四处游动。
　　That is not strong evidence that Ediacarans were Cnidarians, but it is something.
　　这虽然不能有力地证明埃迪卡拉动物属于刺胞动物，但它的确是一个重要的发现。
　　Yet if that is the right interpretation 10, it leaves the question of what evolved into the trilobites and their kind as mysterious as ever.
　　不过倘若这样的解释是正确的，三叶虫和它的同类由何而来的问题将仍然神秘晦涩，一如往昔。