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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Cretaceous Research 37 (2012) 319e340 Contents lists available at SciVerse ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes Review paper A review of the Upper Cretaceous marine reptiles from Japan T. Sato a,*, T. Konishi b, R. Hirayama c, M.W. Caldwell d,e a Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Nukui-Kita-Machi 4-1-1, Koganei City, Tokyo 184-8501, Japan b Royal Tyrrell Museum of Palaeontology, PO Box 7500, Drumheller, Alberta T0J 0Y0, Canada c School of International Liberal Studies, Waseda University, Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-8050, Japan d Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada e Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada article info abstract Article history: Taxonomy and stratigraphic distribution of the Upper Cretaceous marine reptiles from Japan are Received 10 March 2011 reviewed. Remains of the Chelonioidea (sea turtles), Mosasauridae, and Plesiosauria are known in various Accepted in revised form 9 March 2012 parts of Japan, including the holotypes of the dermochelyid Mesodermochelys undulatus, mosasaurine Available online 19 April 2012 Mosasaurus hobetsuensis and M. prismaticus, tylosaurine Taniwhasaurus mikasaensis, and elasmosaurid Futabasaurus suzukii. Less diagnostic materials of other groups such as protostegiids, plioplatecarpines, Keywords: polycotylids, pliosauroids, were also collected. Mesodermochelys dominates the chelonioid fauna, and in Chelonioidea comparison with European and North American faunas, suggests a rather restricted geographical Japan Mosasauridae distribution of chelonioid species during the Late Cretaceous. The mosasaurid records support the world- Plesiosauria wide trend of increasingly mosasaurine-dominated post-Santonian assemblages, and demonstrate Reptilia suprageneric-level compositional changes in the northwestern Pacific through time. Elasmosaurid fossils are known from all stages of the Upper Cretaceous in Japan and indicate their continuous presence in the northwestern Pacific. Polycotylid remains are fewer in number and limited to the lower Upper Cretaceous. Pliosauroid specimens are even rarer but raise the upper limit of the stratigraphic range of the group in Northern Pacific to the Turonian. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction 1988; Oji, 1985; Chinzei, 1986; Maeda, 1991; Tanabe et al., 2003), have been conducted on the marine invertebrates from the Creta- Palaeontological study of Cretaceous marine sediments in Japan ceous of Japan. began in the 19th century with one of the earliest publications being In contrast, the vertebrate fossils from the same strata seem to a descriptive treatise on fossil molluscs (Yokoyama, 1890). A large have attracted much less attention, at least when the number of number of later studies, in particular those by Matsumoto and his academic publications and researchers is compared to those students, established the Japanese Cretaceous as a standard section focused on fossil invertebrates. Early publications date back at least in the circum-Pacific region (e.g., Matsumoto, 1942; Kimura et al., to the 1920s (e.g., Tokunaga and Shimizu, 1926), but scholarly 1993a and references therein). The early emphasis on molluscan articles on Cretaceous marine reptiles have remained few in fossils (e.g., ammonites, bivalves), and later on microfossils number. Those that were published were often provisional studies (e.g., foraminifers, radiolarians) have continued to play major roles in (e.g., Shikama, 1963; Obata et al., 1970, 1972), most likely owing to biostratigraphic zonation, sometimes in combination with magne- the limited availability of specimens and resources (facilities for tostratigraphy for correlation with the global geological timescale preparation, references, comparative material) necessary for the (Toshimitsu et al., 1995). Chemostratigraphy (e.g., Hasegawa, 1997; proper study of Mesozoic reptiles. Uramoto et al., 2007) is a relatively new but promising tool for The situation began to change in the 1980s when descriptive correlation and environmental interpretation. Research in various papers started appearing in professional journals (e.g., Suzuki, other disciplines, such as theoretical and functional morphology, 1985a; Nakaya, 1989a, b), with the number of publications palaeoecology, and taphonomy (e.g., Tanabe, 1979; Okamoto, 1984, increasing dramatically in the 1990s (e.g., Hirayama and Chitoku, 1994, 1996). This trend continued into the first decade of the 21st century (Obata et al., 2007), with descriptions of famous plesiosaur * Corresponding author. Tel.: þ81 42 329 7537; fax: þ81 42 329 7504. and mosasaur specimens, respectively known to the Japanese E-mail address: [email protected] (T. Sato). public as “Futaba Suzuki Ryu” and “Ezo Mikasa Ryu”, finally being 0195-6671/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2012.03.009 Author's personal copy 320 T. Sato et al. / Cretaceous Research 37 (2012) 319e340 published more than 30 years after their initial discoveries (Sato a large number of previously proposed lithostratigraphic nomen- et al., 2006a; Caldwell et al., 2008). clatures (e.g., Kimura et al., 1993a). Thus, after nearly six decades of steady effort by a small but In the classic scheme, the Yezo Supergroup is divided into Lower committed group of researchers, the temporal and spatial biodi- Yezo, Middle Yezo, Upper Yezo, and Hakobuchi Groups, in versity of the Cretaceous marine reptiles of Japan is beginning to ascending order (e.g., Kimura et al., 1993a); this system is widely reveal itself. In this contribution, we review the state of under- used for the current collection records of many fossil specimens. standing of the taxonomy and stratigraphic distribution of the Recently, Takashima et al. (2004) integrated lithostratigraphic and aquatically adapted animals, and attempt to analyze their biogeo- biostratigraphic data and proposed a new scheme in which the graphical significance. entire sequence, now referred to as the Yezo Group, is divided into several formations (the names of certain formations differ in 2. Geological background different areas because of facies changes). The unit boundaries in the two nomenclatures do not necessarily match, and it could lead Japanese Upper Cretaceous marine reptile fossils occur in five to unintentional errors if information contained in one nomencla- major stratigraphical units: the Yezo, Kuji, Futaba, Izumi, and ture was simply converted into another. The stratigraphic infor- fl Goshoura groups (Figs. 1and 2; Table 1). Many of these specimens mation of each specimen provided in this paper re ects the original were excavated by private collectors and donated to local assignments as given in collection data or in publication which museums; therefore, their locality data is based solely on museum often employs the old nomenclature. A generalized, schematic records and/or published accounts. Many specimens from Hok- presentation of the stratigraphic nomenclatures by Kimura et al. fi kaido were collected as float along rivers and creeks, and their (1993a, table 2.13) and Takashima et al. (2004, g. 8) in Fig. 2 fi original horizons cannot be precisely verified; however, the creeks gives rough but suf cient information for an overview of the in the fossil producing areas are generally restricted, and we stratigraphic distribution of the specimens from Hokkaido. consider it is fairly safe to assume that the original horizon is not The Kuji Group in Iwate Prefecture is known for commercial very far from the point of collection. quantities of amber. The group is geologically divided into the The Yezo Group (or Supergroup) exposed in central Hokkaido Tamagawa (non-marine), Kunitan (marine), and Sawayama (non- has so far yielded the largest number of specimens of marine marine) formations (e.g., Kimura et al., 1993a). A few specimens of reptiles from Japan (for reviews of the stratigraphy, see Takashima marine reptiles are known from the Kunitan Formation, a unit that et al., 2004 and Kimura et al., 1993a). The group represents consists largely of sandstones and interpreted as having been AptianeMaastrichtian sediments deposited in a forearc basin, and deposited in nearshore to inner shelf environments; the formation has been subject to intensive biostratigraphic studies because of is dated as Santonian based on molluscan fossils (Terui and the abundant micro- and macrofossils found there since the early Nagahama, 1995). part of the 20th century, and especially after the 1940s. The One of the oldest published accounts on Japanese fossil marine lithology of these units is rather monotonous (primarily consisting reptiles came