The jaw apparatuses of Cretaceous Phylloceratina (Ammonoidea)
The jaw apparatuses of Cretaceous Phylloceratina (Ammonoidea)
复制标题
白垩纪Phylloceratina（Ammonoidea）的颌部装置
作者：
Tanabe;K.;Misaki;A.;Landman;N.H. and Kato;T.
根据日本北海道保存完好的现场资料，描述了晚白垩世Phylloceratina （ammono总科）Hypophylloceras subramosumandPhyllopachyceras ezoensis的两种颚器。大体形态学和x射线CT观察显示，这两个物种的上颚和下颚在整体结构上基本相似。它们的上颚由一个较短的外片和一对较大的、翅膀状的内片组成，这些内片变窄并在前部连接在一起，就像其他菊石一样。然而，这两种甲壳虫的上颌与其他已知的菊科动物的区别在于，它们有一个粗的、箭头状的钙化吻尖。这两个物种的下颚由短而缩小的内片和覆盖着薄钙质层的大而微凸的外片组成，其特征与白垩纪Lytoceratina的rhynchaptychus型下颚相同。在上颚和下颚上都有一个尖锐的、厚的钙质尖端，这表明Phylloceratina的颌部器官类似于现代和化石的鹦鹉螺，这表明它们是为了在更深的海洋环境中觅食而发展起来的。这一研究和其他研究表明，至少有一些中生代的纹石岩和贝壳鸟可归因于层角虫和Lytoceratina。
The jaw apparatuses of two species of Late Cretaceous Phylloceratina (Ammonoidea),Hypophylloceras subramosumandPhyllopachyceras ezoensis,are described on the basis of well-preservedin situmaterial from Hokkaido, Japan. Gross morphological and X-ray CT observations reveal that the upper and lower jaws of the two species are essentially similar in their overall structure. Their upper jaws consist of a shorter outer lamella and a pair of larger, wing-like inner lamellae that become narrower and join together in the anterior portion, as in those of other ammonoids. The upper jaws of the two phylloceratid species are, however, distinguishable from those of other known ammonoids by the presence of a thick, arrowhead-shaped calcified rostral tip. The lower jaws of the two species consist of a short, reduced inner lamella and a large, gently convex outer lamella covered with a thin calcareous layer, the features of which are common with the rhynchaptychus-type lower jaws of the Cretaceous Lytoceratina. In the presence of a sharply pointed, thick calcareous tip on upper and lower jaws, the jaw apparatuses of the Phylloceratina resemble those of modern and fossil nautilids, suggesting that they were developed to serve a scavenging predatory feeding habit in deeper marine environments. This and other studies demonstrate that at least some Mesozoic rhyncholites and conchorhynchs are attributable to the Phylloceratina and Lytoceratina.