Kanno, Shiori, Nakajima, Yasuhisa, Hikida, Yoshinori, and Sato, Tamaki (2017) Sphenodus (Chondrichthyes, Neoselachii) from the Upper Cretaceous in Nakagawa Town, Hokkaido, Japan. Paleontological Research, 21 (2). pp. 122-130.

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Abstract

Eight specimens of Sphenodus have been collected from the Upper Cretaceous, Coniacian of Nakagawa Town in Hokkaido, northern Japan. They are referred to as S. cf. lundgreni and Sphenodus spp. 1 and 2, and described in detail. Nearly complete specimens of Sphenodus were previously unknown from the Cretaceous in the Pacific region, and the Nakagawa specimens are the first to exhibit distinct root morphologies, which allow comparison at the species level. A review of the occurrences of this genus reveals that their distribution concentrates in the mid- to high palaeolatitude regions. This distributional pattern of Sphenodus may represent its preference for colder water and possibly explains the extinction of this genus across the Paleocene-Eocene boundary, when the thermal maximum began.

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