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A primitive fish from the Cambrian of North America

机译：来自北美寒武纪的原始鱼类

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Knowledge of the early evolution of fish largely depends on soft-bodied material from the Lower (Series 2) Cambrian period of South China1, 2. Owing to the rarity of some of these forms and a general lack of comparative material from other deposits, interpretations of various features remain controversial, as do their wider relationships amongst post-Cambrian early un-skeletonized jawless vertebrates. Here we redescribe Metaspriggina on the basis of new material from the Burgess Shale and exceptionally preserved material collected near Marble Canyon, British Columbia, and three other Cambrian Burgess Shale-type deposits from Laurentia. This primitive fish displays unambiguous vertebrate features: a notochord, a pair of prominent camera-type eyes, paired nasal sacs, possible cranium and arcualia, W-shaped myomeres, and a post-anal tail. A striking feature is the branchial area with an array of bipartite bars. Apart from the anterior-most bar, which appears to be slightly thicker, each is associated with externally located gills, possibly housed in pouches. Phylogenetic analysis places Metaspriggina as a basal vertebrate, apparently close to the Chengjiang taxa Haikouichthys and Myllokmuningia, demonstrating also that this primitive group of fish was cosmopolitan during Lower-Middle Cambrian times (Series 2-3). However, the arrangement of the branchial region in Metaspriggina has wider implications for reconstructing the morphology of the primitive vertebrate. Each bipartite bar is identified as being respectively equivalent to an epibranchial and ceratobranchial. This configuration suggests that a bipartite arrangement is primitive and reinforces the view that the branchial basket of lampreys is probably derived. Other features of Metaspriggina, including the external position of the gills and possible absence of a gill opposite the more robust anterior-most bar, are characteristic of gnathostomes and so may be primitive within vertebrates.
机译：关于鱼类早期进化的知识很大程度上取决于中国南方下（系列2）寒武纪1、2的软质物质。由于其中某些形式的稀有性以及其他矿床普遍缺乏可比材料，因此各种特征之间的争议仍然存在争议，在寒武纪后早期未骨骼化的无颚脊椎动物中它们之间的广泛关系也存在争议。在这里，我们根据Burgess页岩中的新材料以及在不列颠哥伦比亚省大理石峡谷和Laurentia的其他三个Cambrian Burgess页岩型矿床中收集的特有保存的材料，对Metaspriggina进行了重新描述。这种原始的鱼类显示出明确的脊椎动物特征：脊索，一对突出的照相机型眼睛，成对的鼻囊，可能的头盖骨和弓形虫，W形的单体和肛门后的尾巴。一个引人注目的特征是分支区域带有两部分条的阵列。除了最前面的杆（看起来稍粗一些）以外，每个杆都与可能位于小袋中的位于外部的g相关联。系统发育分析表明，Metaspriggina是一种基础脊椎动物，显然靠近澄江类群Haikouichthys和Myllokmuningia，也表明该原始鱼类群在下中寒武世时期是世界性的（2-3系列）。然而，后骨的分支区域的安排对重建原始脊椎动物的形态具有更广泛的意义。每个二分棒被识别为分别等效于支气管上支和ceratobranchial。这种配置表明，二部安排是原始的，并加强了七lamp鳗分支篮子可能派生的观点。 Metaspriggina的其他特征，包括the的外部位置以及与最坚固的最前面的横条相对的possible的可能缺失，是钩吻动物的特征，因此可能在脊椎动物中很原始。

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  • 来源
    《Nature》 |2014年第7515期|419-422|共4页
  • 作者

    Simon Conway Morris; Jean-Bernard Caron;

  • 作者单位

    Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK;

    Department of Natural History (Palaeobiology), Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada, University of Toronto, Department of Ecology and Evolutionary Biology, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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