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Paleontological Research
Abstract
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.
We thank Shoji Hayashi of Osaka Museum of Natural History for assisting our fieldwork, also Taketeru Tomita of Okinawa Churashima Research Center and Ryoko Matsumoto, Hiroshi Senou, Hajime Taru, and Mitsuharu Oshima of Kanagawa Prefectural Museum of Natural History for advice on shark taxonomy and access to the comparative modem specimens under their care. Review comments from Yoshitaka Yabumoto and Diogo Mayrinck were helpful to improve the manuscript. This research was financially supported by Nakagawa Town, Tokyo Gakugei University, JSPS KAKENHI Grant Number 15K05327 to T.S.) and JSPS Postdoctoral Fellowships for Research Abroad (programme no. 25.498 to Y.N.).
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