Late Cretaceous Record of Large Soft-Bodied Coleoids Based on Lower Jaw Remains from Hokkaido, Japan
Late Cretaceous Record of Large Soft-Bodied Coleoids Based on Lower Jaw Remains from Hokkaido, Japan
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DOI：
10.4202/app.00057.2013
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发表时间：
2014-03
期刊：
影响因子：
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通讯作者：
K. Tanabe;A. Misaki;T. Ubukata
中科院分区：
文献类型：
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作者：
K. Tanabe;A. Misaki;T. Ubukata
大多数现代鞘翅目类群的起源和系统发育关系还没有被可靠的化石证据所解释，这在很大程度上是因为在它们的进化历史中，钙化的腔壳减少或消失。本文描述了产于日本北海道晚白垩世地层中的两个异常巨大的鞘翅目下颚化石。通过对现代和化石鞘翅目下颌骨的形态学和形态计量学资料的比较，我们将这两个下颌骨分别归属于以下新的分类单元：弯形目Nanaimoteuthis hikidai sp. nov.和十臂目Teuthida gen. et sp. nov.。N. hikidai与来自温哥华岛（加拿大）和北海道的上白垩纪的同属的其他物种的区别在于具有更宽的、更向前弯曲的外片层的罩。H.波塞冬似乎表现出像现代条虫和乌贼一样的镶嵌特征，但根据外部薄片的整体形状和侧壁上明显褶皱的发展，波塞冬被分配给条虫。由于异常大的下颚，这些新的分类群似乎在身体大小与现代巨型鱿鱼（Architeuthis spp.）和洪堡鱿鱼（Dosidicus gigas）。这一发现和其他发现的大型颌骨，可与北太平洋上白垩纪地层中的腕足和十臂类鞘翅目动物相媲美，填补了主要是软体鞘翅目动物化石记录相对贫乏的差距。
The origin and phylogenetic relationships of most modern coleoid groups have not yet been explained by reliable fossil evidence, in large part because of the reduction or disappearance of a calcified chambered shell during their evolutionary history. Herein we describe two exceptionally large coleoid lower jaws from the Upper Cretaceous strata in Hokkaido, Japan. On the basis of the comparison of gross morphology and morphometric data of the lower jaws of modern and fossil coleoids, we assigned the two lower jaws to the following new taxa: Nanaimoteuthis hikidai sp. nov. of the order Vampyromorpha (superorder Octobrachia) and Haboroteuthis poseidon gen. et sp. nov. of the order Teuthida (superorder Decabrachia). The lower jaw of N. hikidai is distinguished from other species of the same genus from the Upper Cretaceous of Vancouver Island (Canada) and Hokkaido by having a broader, more anteriorly curved hood of the outer lamella. The lower jaw of H. poseidon seemingly exhibits mosaic features like those of modern teuthids and sepiids but is assigned to Teuthida on the basis of the overall shape of the outer lamella and the development of a distinct fold on the lateral wall. Because of the unusually large lower jaws, these new taxa appear to be comparable in body size to modern giant squids (Architeuthis spp.) and the Humboldt squid (Dosidicus gigas). This and other discoveries of large jaws referable to octobrachian and decabrachian coleoids from the Upper Cretaceous strata of the North Pacific fill the gap in the relatively poor fossil record of mainly soft-bodied coleoids.