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.
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Paleontological Research
Vol. 20 • No. 2
April 2016
Vol. 20 • No. 2
April 2016
Cretaceous/Paleogene boundary
Diplomoceras cylindraceum
Kawaruppu Formation
Maastrichtian
Nemuro Group
north Pacific region