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本文选自《经济学人》9月12日刊文章。鲨鱼是软骨鱼，它没有鱼鳔，但较轻的骨架能让它在水中、在不同的深度下灵活游动，这让它成为第一个全球性鱼类物种之一。从进化的角度来说，软骨是一种非常成功的策略，但是后来进化出鱼鳔的硬骨鱼才是殖民陆地的各种物种的祖先。在漫长的历史中，用来调节浮力的鱼鳔后来变成原始的肺，硬骨鱼从而进化成两栖类动物，进而进化成陆地生物。但最近在蒙古国境内发现的一块4.10亿年前的化石表明，软骨鱼和硬骨鱼的祖先都有能力长出坚硬的骨骼，只不过在后来的历史中，软骨鱼不知为何失去了硬骨。 
选文精讲 How the shark forgot his skeletonBony skeletons may be even older than palaeontologists thoughtVERTEBRATES—THOSE animals with a backbone—are a diverse bunch, encompassing everything from tuna and budgerigars to snakes, chinchillas and human beings. One way biologists divide them up concerns the composition of their skeletons. Most vertebrates sport hard, calcified bones, and are dubbed the osteichthyans. A second, much smaller category is the chondrichthyans, whose members include sharks, rays and skate. Unlike their hard-boned cousins, chondrichthyans make do with structural parts made of soft, tough cartilage.- sport: 这里做为动词“显示、显摆”的意思，eg. He is sporting a nice beard. 他留着漂亮的胡子；He is sporting a nice suit. 他在显摆一件漂亮的西装。
脊椎动物——是指那些有脊椎的动物——是一个多元的群体，包括金枪鱼、虎皮鹦鹉、蛇、南美栗鼠和人类。生物学家将它们分类的一种方法是根据它们骨骼的组成。大多数脊椎动物都有坚硬、钙化的骨头，被称为硬骨鱼类。第二种小得多的种类是软骨鱼类，它的成员包括鲨鱼、鳐鱼和扁体鱼。软骨鱼不同于它们骨骼坚硬的表亲，它们需要设法使用由柔软而坚韧的软骨组成的结构部分。Palaeontologists had long assumed that cartilage was the more primitive arrangement. Osteichthyan fetuses, after all, begin life with a cartilaginous skeleton that is gradually replaced by harder, more durable bone as they grow. But a paper just published in Nature Ecology & Evolution suggests that view may be mistaken. In it a team led by Martin Brazeau of Imperial College London describe the discovery of a 410m-year-old fossil in Turgen, a district of Mongolia close to the Russian border. The fossil is the partial skull of a new species of placoderm, a type of armoured fish, which Dr Brazeau and his colleagues have dubbed Minjinia turgenensis.长期以来，古生物学家一直认为软骨是更为原始的结构。毕竟，硬骨鱼类胎儿的生命开始时是软骨骨骼，随着生长逐渐被更坚硬、更持久的骨骼所取代。但是，刚刚发表在《自然生态与进化》上的一篇论文表明，这种观点可能是错误的。在报告中，伦敦帝国理工学院的Martin Brazeau领导的团队描述了在靠近俄罗斯边境的蒙古国境内发现了一块4.10亿年前的化石。这块化石是一种新物种盾皮鱼的部分头骨，盾皮鱼是一种鳞甲鱼，Brazeau博士和他的同事们将其命名为Minjinia turgenensis。
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