Microstructure and mineralogy of the outer calcareous layer in the lower jaws of Cretaceous Tetragonitoidea and Desmoceratoidea (Ammonoidea)
Microstructure and mineralogy of the outer calcareous layer in the lower jaws of Cretaceous Tetragonitoidea and Desmoceratoidea (Ammonoidea)
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白垩纪四角石总科和锁角角石总科（菊石总科）下颌外钙质层的显微结构和矿物学
DOI：
10.1111/j.1502-3931.2011.00272.x
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发表时间：
2012
期刊：
影响因子：
1.5
通讯作者：
I.
中科院分区：
文献类型：
--
作者：
Tanabe;K.;Landman;N.H. and Kruta;I.
根据它们的相对大小、整体形状、结构和外部钙化覆盖物的发育程度的差异，将Ammonoidea的下颌分为正常型、近颚型、近颚型和舌颚型四种形态。然而，这些形态的详细微观结构和矿物学比较尚未得到解决。本文记录了三种晚白垩世菊科菊科（Anagaudryceras limatum）和菊科（Pachydiscus kamishakensisandDamesitesaff）菊科菊科菊科的下颚的SEM和XRD观察结果。Sugata)，基于保存在体腔内的优质材料，并保留文石壳壁。这三个物种的下颌被划分为前两个物种的近颚龙和近颚龙类型和第三个物种的舌颚龙类型之间的中间形态。它们黑色的，可能原本是几丁质的外层薄片完全被钙质层覆盖。钙质层主要由文石、灰岩、砂砾、灰岩组成。石灰石和方解石。kamishakensis。三种类型的外钙质层微观结构不同，均为粒状inA。柱顶，球晶柱状柱顶，柱顶柱状柱顶。这些特征都可以从某些侏罗纪和白垩纪Ammonitina和Ancyloceratina的典型aptychus型下颌的外成对钙质板的板状和海绵状结构中区分出来。我们的研究表明，侏罗纪和白垩纪的菊石在其下颚处具有一层外钙质层，尽管其矿物学、微观结构和相对厚度在不同分类群之间存在差异。
Based on the differences in their relative size, overall shape, structure and the degree of development of an outer calcified covering, lower jaws of the Ammonoidea have been classified into four morphotypes: normal, anaptychus, aptychus and rhynchaptychus types. However, detailed microstructural and mineralogical comparison of these morphotypes has not yet been addressed. This article documents the results of SEM and XRD observations of the lower jaws of three Late Cretaceous ammonoid species belonging to the Tetragonitoidea (Anagaudryceras limatum) and Desmoceratoidea (Pachydiscus kamishakensisandDamesitesaff.sugata), based on excellent material preservedin situwithin the body chamber, and retaining an aragonitic shell wall. The lower jaws of the three species are assigned to an intermediate form between anaptychus and aptychus types for the first two species and the rhynchaptychus type for the third species. Their black, presumably originally chitinous outer lamella is wholly covered with a calcareous layer. The calcareous layer is composed of aragonite inD.aff.sugataandA. limatum, and calcite inP. kamishakensis. The microstructure of the outer calcareous layer differs among the three species, i.e. granular inA. limatum,spherulitic prismatic inD. sugata, and prismatic inP. kamishakensis, all of which can be distinguished from the lamellar and spongy structure of the outer-paired calcitic plates of the typical aptychus-type lower jaws in some Jurassic and Cretaceous Ammonitina and Ancyloceratina. Our study suggests that most Jurassic and Cretaceous ammonoids possessed an outer calcareous layer in their lower jaws, although its mineralogy, microstructure and relative thickness vary among different taxa.