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New Ideas About Old Sharks

机译：关于旧鲨鱼的新想法

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The world's oceans, lakes and riv-ers harbor about 30,000 species of fish. In addition to a diverse array of bony fishes, scientists have described some 830 species of Chondrichthyes— sharks, skates, rays and other cartilaginous fishes. Many paleobiologists are working to decipher the fossil record left by the bony fish—our ancestors after all, and what we generally find on the end of a fishing line. Others are concerned with the mysterious and closely connected story of how the sharks and their relatives came to be. Chondrichthyans are remnants of an ancient lineage, rare survivors from an explosion of forms that mostly disappeared before the end of the Devonian Period, 359 million years ago. Thanks to the rarity of intact shark fossils, the transition from primitive fish to sharks and bony fishes is poorly understood. Following the discovery of a relatively complete early shark fossil, paleontologists hope to better understand this important evolutionary progression. Initial examination of the fossil led to surprising implications. First, it became clear that early sharks were more diverse than scientists had imagined. Next, the presence of pectoral spines on the new fossil suggests that relationships among bony and cartilaginous species might be somewhat closer and also rnore complex than had been thought. Thus, this type of shark could help scientists work out the evolution of bony fishes, the Osteichthyes. This and other fossils being discovered around the world look set to revolutionize our view of early shark and fish evolution.
机译：世界上的海洋，湖泊和河流约有30,000种鱼类。除了各种各样的骨鱼类外，科学家还描述了约830种软骨鱼类，包括鲨鱼，滑冰，skate鱼和其他软骨鱼类。许多古生物学家正在努力破译硬骨鱼类（毕竟是我们的祖先）留下的化石记录，以及我们通常在钓鱼线末端发现的东西。其他人则关注鲨鱼及其亲属的神秘而紧密联系的故事。软骨鱼类是古老血统的残余，是在3.59亿年前泥盆纪时代结束之前就消失了的形态爆炸的稀有幸存者。由于完整的鲨鱼化石非常稀少，人们对从原始鱼到鲨鱼和骨鱼的过渡知之甚少。在发现了相对完整的早期鲨鱼化石之后，古生物学家希望更好地了解这一重要的进化过程。化石的初步检查产生了令人惊讶的影响。首先，很明显，早期的鲨鱼比科学家想象的要多样化。接下来，新化石上胸鳍的存在表明，骨和软骨物种之间的关系可能比以前想象的更紧密，也更复杂。因此，这种类型的鲨鱼可以帮助科学家弄清楚骨鱼类Osteichthyes的进化。在世界各地发现的这种化石和其他化石看起来将彻底改变我们对鲨鱼和鱼类早期进化的看法。

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