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Paleontological Research
Abstract
Abstract.
This paper describes the first record of the heteromorph ammonoid Diplomoceras cylindraceum from the uppermost Maastrichtian Kawaruppu Formation of the Nemuro Group, southeastern Hokkaido, Japan. D. cylindraceum was found in a siltstone 15 m below the Cretaceous/Paleogene (K/Pg) boundary. The stratigraphical level of the fossil is estimated to be ∼66.8 Ma, based on the time scale for the geomagnetical polarity and the K/Pg boundary. D. cylindraceum, therefore, was living at least ∼0.8 m.y. before the K/Pg boundary event in the north Pacific region.
We are grateful to Marcin Machalski (Instytut Paleobiologii, Poland) and Akihiro Misaki (Kitakyushu Museum of Natural History and Human History) for helpful reviews that led to improvement of the manuscript. We thank Ryoji Wani (Yokohama National University) for critical reading of the early manuscript. We also thank Makoto Mochida (Historical Museum of Urahoro) for registering the specimen and Shin'ichi Maruko for supporting our field work. This research is supported by a grant from the Section of Curators, the Hokkaido Museum Association.
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