Late Cretaceous Octobrachiate Coleoid Lower Jaws from the North Pacific Regions
Late Cretaceous Octobrachiate Coleoid Lower Jaws from the North Pacific Regions
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北太平洋地区的白垩纪晚期八臂动物胶体下颌
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
Y. Hikida
中科院分区：
文献类型：
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作者：
K. Tanabe;P. Trask;R. Ross;Y. Hikida
在加拿大温哥华岛和日本北海道晚白垩世（Santonian和Campanian）沉积中发现了8个保存完好的头足类颌骨化石。它们单独出现在钙质结核中，并保留其三维结构。其中7个由一个广泛开放的外板和一个向后突出的内板与尖喙。这两个薄片都是由氟磷灰石，这可能代表成岩改变甲壳素，并缺乏钙质元素。根据这些特征，这七块颌骨化石被鉴定为鞘翅目的下颚。通过与现代鞘翅目的下颚比较，我们可以区分出以下新属和新种：吸血目的Nanaimoteuthis jeletzkyi，以及环足目的Paleocirroteuthis hagarti和P. pacifica。这些新分类群的下颚明显区别于现代和灭绝的十臂总目和足目的下颚，因为它们的内片突出得少得多。它们的最大外片层长度（35.0-67.1毫米）远大于大多数现代吸血虫和蔓足类物种，表明它们的主人体型大，体重重。其他三个下颌检查，其特点是向后延伸的外板，可能被分配到后足。这一研究清楚地表明，大型的腕足类鞘虫存在于晚白垩世北太平洋。
Abstract Eight well-preserved cephalopod jaw fossils were discovered from the Upper Cretaceous (Santonian and Campanian) deposits of Vancouver Island, Canada, and Hokkaido, Japan. They occur individually in calcareous concretions and retain their three-dimensional architecture. Seven of them consist of a widely open outer lamella and a posteriorly projected inner lamella with a pointed rostrum. Both lamellae are made of fluorapatite, which may represent diagenetically altered chitin, and lack a calcareous element. Based on these diagnostic features, the seven jaw fossils are identified as lower jaws of the Coleoidea. Comparison with the lower jaws of modern coleoids allows us to distinguish the following new genera and species among them; Nanaimoteuthis jeletzkyi of the Order Vampyromorphida, and Paleocirroteuthis haggarti and P. pacifica of the Order Cirroctopodida. The lower jaws of these new taxa are clearly distinguished by having a much less projected inner lamella from those of modern and extinct species of the Superorder Decabrachia and the Order Octopodida. The maximum lengths of their outer lamellae (35.0–67.1 mm) are much larger than those of most modern vampyromorph and cirroctopodid species, indicating the large body size and weight of their owners. One of the other three lower jaws examined, characterized by a posteriorly extended outer lamella, may be assigned to the Octopodida. This study clearly demonstrates that large octobrachiate coleoids existed in the Late Cretaceous North Pacific.