Beaks and radulae of Early Carboniferous goniatites
Beaks and radulae of Early Carboniferous goniatites
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早石炭世尖角岩的喙和齿齿
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
H. Mutvei
中科院分区：
文献类型：
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作者：
L. Doguzhaeva;R. Mapes;H. Mutvei
用光学显微镜和扫描电子显微镜对阿肯色州密西西比晚期(早石炭世)约100个角闪石喙(颌骨)和5个齿状突进行了研究。在角闪石Girtyocera的身体腔内发现了四个喙。由于三维保存，这些已知最古老的喙可以被详细研究，并与活着的海鞘中的喙进行比较。喙是单瓣的，下部的比上部的大。每个喙由一个有机的外板和内板组成，只有嘴是弱钙化的。在下喙中，外叶和内叶的长度大致相同，但在上喙中，外叶比内叶短得多。角闪石喙在上喙内外板层的相对长度上与活着的角闪石喙相似，这可能表明肌肉插入上的相似之处。关于内、外板的长度，其下喙与Vampyroteuth和远洋章鱼的下喙相似。这里讨论的晚密西西比角闪石喙在总体形态上与石炭纪和二叠纪的角闪石相似，但不同于中生代的菊石。在后一种菊石中，下喙有一个长的外板和一个短的内板，而在角闪石中，这两个板的长度大致相等。角闪石在菊石演化过程中保持稳定，并与活着的珊瑚中的角闪石显示出或多或少的相似性。
About one hundred goniatite beaks (jaws) and five radulae from the Late Mississippian (Early Carboniferous) of Arkansas wgere studied with light and scanning electron microscopy (SEM). Four beaks were found within the body chamber of the goniatite Girtyoceras. Owing to the three-dimensional preservation, these oldest known beaks could be studied in detail and compared with those in living coleoids. The beaks are univalved, and the lower one is larger than the upper. Each beak consists of an organic outer and inner lamella; only the rostrum is weakly calcified. In the lower beak the outer and inner lamellae are about the same length, but in the upper beak the outer lamella is considerably shorter than the inner lamella. The goniatite beaks resemble those in living coleoids in the relative length of the outer and inner lamellae in the upper beak, which probably indicates similarity in muscle insertion. Concerning the length of the inner and outer lamellae, the lower beak is similar to that in Vampyroteuthis and the pelagic octopod Tremoctopus. Late Mississippian goniatite beaks dealt with here are similar to those of Carboniferous and Permian goniatites in general morphology, but differ from those of Mesozoic ammonoids. In the latter ammonoids, the lower beak has a long outer lamella and a short inner lamella, whereas both lamellae have about equal length in the goniatites. Goniatite radulae remain stable during ammonoid evolution and demonstrate a more or less distinct similarity with those in living coleoids.