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1 2 3 4 5 6 Discovery of the heteromorph ammonoid Amapondella amapondense in the middle 7 8 9 Campanian of Hokkaido, Japan 10 11 12 13 14 15 YASUNARI SHIGETA1 and MASATAKA IZUKURA2 16 Accepted manuscript 17 18 19 20 21 1Department of Geology and Paleontology, National Museum of Nature and Science, 22 23 24 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan (e-mail: [email protected]) 25 26 27 2N28 E21-1-3, Higashi-ku, Sapporo, Hokkaido 065-0028, Japan 28 29 30 31 32 33 Abstract. The discovery of the heteromorph ammonoid Amapondella amapondense 34 35 36 (van Hoepen) in the lower middle Campanian in the Urakawa, Biratori and 37 38 39 Hidaka areas of Hokkaido, northern Japan, represents the first report of this 40 41 42 taxon in the Northwest Pacific region. Because the species flourished in other 43 44 45 regions during Santonian to early Campanian time, its final geographic occurrence 46 47 48 in Hokkaido suggests that global environmental changes likely had a significant 49 50 51 influence on ammonoid biogeography during early middle Campanian time. 52 53 54 55 56 57 Keywords: Amapondella, ammonoid, biogeography, Campanian, , 58 59 60

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1 2 3 4 5 6 Hokkaido 7 8 9 10 11 12 Introduction 13 14 15 16 Accepted manuscript 17 18 The shell of the monospecific Cretaceous heteromorph ammonoid genus 19 20 21 Amapondella Klinger and Kennedy, 1997 (type species Heteroceras amapondense van 22 23 24 Hoepen, 1921) is characterized by its tightly coiled helical phragmocone, which forms a 25 26 27 low helix and a body chamber that curves upward until it reaches or slightly exceeds the 28 29 30 height of the apex of the helical whorls (Klinger and Kennedy, 2003). The genus was 31 32 33 first proposed as a subgenus of the genus Matsumoto, 1967, but then 34 35 36 was treated as an independent genus (e.g. Klinger et al., 2007). Specimens assigned to 37 38 39 the genus are known from the Santonian of Europe, the Middle East, southern Africa, 40 41 42 Madagascar, southern USA, Pacific Coast of Canada and the lower Campanian offshore 43 44 45 deposits of Madagascar and south of KwaZulu-Natal, southern Africa (Klinger and 46 47 48 Kennedy, 2003; Haggart and Graham, 2018). 49 50 51 Coauthor Masataka Izukura recently discovered two specimens referable to 52 53 54 Amapondella amapondense in the lower middle Campanian in the Biratori and Hidaka 55 56 57 areas, south-central Hokkaido, northern Japan (Figure 1). The late Hide Kubota 58 59 60

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1 2 3 4 5 6 collected two specimens referable to this species from the lower middle Campanian in 7 8 9 the Urakawa area, southern central Hokkaido and the specimens were subsequently 10 11 12 donated to the Hobetsu Museum (Mukawa, Hokkaido) by his wife Katsuko Kubota. We 13 14 15 herein describe these four specimens and discuss their biogeographical significance. 16 Accepted manuscript 17 18 19 20 21 Notes on stratigraphy 22 23 24 25 26 27 The Upper Cretaceous Chinomigawa Formation of the Yezo Group, which is 28 29 30 composed mainly of sandy mudstone and mudstone with sandstone, is widely 31 32 33 distributed in the Urakawa area (Matsumoto, 1942; Kanie, 1966; Sakai and Kanie, 34 35 36 1986; Kanie and Sakai, 2002; Shigeta et al., 2016), and sporadic outcrops occur in the 37 38 39 Niikappu–Biratori–Hidaka areas of south-central Hokkaido (Shigeta et al., 2019). These 40 41 42 sporadic outcrops were originally described as the Hakobuchi Group in Yoshida et al. 43 44 45 (1959) and Takahashi and Suzuki (1978, 1986). 46 47 48 The Chinomigawa Formation in the Urakawa area was divided into four members 49 50 51 (U2–U5, Sakai and Kanie, 1986), and the lower two members (U2 and U3) are well 52 53 54 exposed along the southern coast of Ikantai, 3 km west–northwest of Urakawa 55 56 57 (Matsumoto and Kanie, 1982; Wada et al., 1992). Member U2 contains Sphenoceramus 58 59 60

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1 2 3 4 5 6 orientalis (Sokolov, 1914) in the upper part and Member U3 includes S. schmidti 7 8 9 (Michael, 1899). Both fossils are index inoceramids of early middle Campanian time in 10 11 12 the Northwest Pacific region, an age assignment confirmed by both magnetostratigraphy 13 14 15 and zircon geochronology (e.g. Kodama, 1990; Shigeta and Tsutsumi, 2018). Outcrops 16 Accepted manuscript 17 18 of the portion of the formation yielding S. orientalis and S. schmidti are exposed in a 19 20 21 narrow area in the middle course of the Soushubetsu River in the Biratori area (Yoshida 22 23 24 et al., 1959) and are widely distributed in the upper course of the Pankeushappu River 25 26 27 in the Hidaka area (Takahashi and Suzuki, 1986). 28 29 30 The four Amapondella amapondense specimens of the present study were 31 32 33 collected from the Chinomigawa Formation in the following areas: two specimens from 34 35 36 float calcareous concretions found along the southern coast of Ikantai in the Urakawa 37 38 39 area together with Sphenoceramus orientalis, one specimen from an exposure along the 40 41 42 middle course of the Soushubetsu River in the Biratori area that also contained the early 43 44 45 middle Campanian ammonoid Urakawaites sp. and one specimen from a float 46 47 48 calcareous concretion found in the upper course of the Pankeushappu River in the 49 50 51 Hidaka area together with S. orientalis. 52 53 54 55 56 57 Paleontological description 58 59 60

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1 2 3 4 5 6 7 8 9 Systematic descriptions follow the classification established by Wright et al. 10 11 12 (1996). Morphological terms in the systematic description are those used in Arkell 13 14 15 (1957). 16 Accepted manuscript 17 18 Institution abbreviations.—HMG, Hobetsu Museum, Mukawa. 19 20 21 22 23 24 Suborder Wiedmann, 1966 25 26 27 Superfamily Gill, 1871 28 29 30 Family Hyatt, 1894 31 32 33 Genus Amapondella Klinger and Kennedy, 1997 34 35 36 37 38 39 Type species.—Heteroceras amapondense van Hoepen, 1921. 40 41 42 Remarks.—Amapondella was first proposed as a subgenus of Eubostrychoceras 43 44 45 by Klinger and Kennedy (1997), but Klinger et al. (2007) later elevated the taxon to an 46 47 48 independent genus. We herein follow the interpretation of Klinger et al. (2007). 49 50 51 52 53 54 Amapondella amapondense (van Hoepen, 1921) 55 56 57 Figures 2–4 58 59 60

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1 2 3 4 5 6 7 8 9 Heteroceras amapondense van Hoepen, 1921, p. 17, pl. 4, figs. 1, 2. 10 11 12 Eubostrychoceras (Amapondella) amapondense (van Hoepen). Klinger and Kennedy, 13 14 15 2003, p. 235, figs. 5, 6, 7A, 8A–D, 9A–C (with synonymy). 16 Accepted manuscript 17 18 Amapondella amapondense (van Hoepen). Klinger et al., 2007, p. 101, figs. 5A–C, 19 20 21 10I–J, 11, 12B–I, 13A–E, M (with synonymy); Schaffert and Larson, 2021, p. 31, 22 23 24 figs. 43–49. 25 26 27 Amapondella cf. amapondense (van Hoepen). Haggart and Graham, 2018, fig. 5. 28 29 30 31 32 33 Type.—The holotype, figured by van Hoepen (1921, p. 17, pl. 4, figs. 1, 2), from 34 35 36 the upper Santonian or lower Campanian of the Mzamba Formation at the Mzamba 37 38 39 River Estuary, Pondoland, Eastern Cape Province, South Africa, is curated in Ditsong 40 41 42 Museum of Natural History, Pretoria. 43 44 45 Material examined.—HMG-2014 was extracted from a calcareous concretion 46 47 48 found in the middle course of the Soushubetsu River (42°39′17.85″N, 142°25′12.44″E), 49 50 51 in the Biratori area. HMG-2015 was extracted from a float calcareous concretion found 52 53 54 5.25 km upriver from the mouth of the Pankeushappu River (42°54′52.05″N, 55 56 57 142°25′15.17″E), a branch of the Saru River, in the Hidaka area. HMG-2016 and 58 59 60

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1 2 3 4 5 6 HMG-2017 were extracted from float calcareous concretions found along the southern 7 8 9 coast of Ikantai in the Urakawa area. 10 11 12 Description.—HMG-2014 (Figure 2A–F), consisting of almost half of 60 mm 13 14 15 diameter helical phragmocone. Earliest whorls, less than about 5 mm in diameter, not 16 Accepted manuscript 17 18 preserved. Preserved initial three whorls (about 30 mm in diameter) helically and tightly 19 20 21 coiled dextrally, forming apical angle of approximately 95°. As shell grows, apical 22 23 24 angle becomes lower, 112° on the fourth whorl (about 60 mm in diameter). Whorl cross 25 26 27 section nearly circular. Shell surface ornamented with dense, regularly spaced, normal 28 29 30 ribs and strong, highly elevated, flared ribs occurring between every 2–3 normal ribs. 31 32 33 Ribs slightly oblique, narrowly raised with slightly concave interspaces, and 34 35 36 symmetrical in cross section with respect to adoral direction. 37 38 39 HMG-2016 (Figure 2G–I), consisting of a fragment of a phragmocone and a part 40 41 42 of the body chamber. Coiling helical and dextral, forming low apical angle with whorls 43 44 45 touching. Whorl cross section nearly circular. Shell surface ornamented with dense, 46 47 48 regularly spaced, normal ribs and flared ribs occurring every 5–6 normal ribs. Ribs 49 50 51 slightly oblique, narrowly raised with slightly concave interspaces, and symmetrical in 52 53 54 cross section with respect to adoral direction. 55 56 57 HMG-2015 (Figure 3), consisting of a phragmocone with a diameter of about 60 58 59 60

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1 2 3 4 5 6 mm and a fragment of body chamber with length of about 300°. Early whorls, less than 7 8 9 about 15 mm in diameter, not preserved. Middle whorls (phragmocone), 15–60 mm in 10 11 12 diameter, helically and tightly coiled dextrally, forming low apical angle of 13 14 15 approximately 150°. Body chamber gradually grows downward and is located below in 16 Accepted manuscript 17 18 contact with the previous whorls. Whorl cross section nearly circular. Shell surface 19 20 21 ornamented with dense, regularly spaced, normal ribs and flared ribs occurring between 22 23 24 every 4–5 normal ribs. Ribs slightly oblique on phragmocone and early part of body 25 26 27 chamber, but rursiradiate on lower whorl face on the remaining body chamber, narrowly 28 29 30 raised with slightly concave interspaces, and symmetrical in cross section with respect 31 32 33 to adoral direction. 34 35 36 HMG-2017 (Figure 4), consisting of a phragmocone with a diameter of 68 mm 37 38 39 and a part of the body chamber with length of about 210°. Early whorls, less than about 40 41 42 15 mm in diameter, not preserved. Middle whorls (phragmocone), 15–68 mm in 43 44 45 diameter, helically and tightly coiled dextrally, forming low apical angle of 46 47 48 approximately 150°. Because the body chamber is broken at 90° from last septum, the 49 50 51 ensuring part not in contact with the previous whorls. Whorl cross section nearly 52 53 54 circular. Shell surface ornamented with dense, regularly spaced, normal ribs and flared 55 56 57 ribs occurring every 3–7 ribs. Ribs slightly oblique, narrowly raised with slightly 58 59 60

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1 2 3 4 5 6 concave interspaces, and symmetrical in cross section with respect to adoral direction. 7 8 9 Remarks.—Klinger and Kennedy (2003, Figs. 6, 7A) illustrated a complete 10 11 12 specimen of Amapondella amapondense from the lower Campanian of South Africa. 13 14 15 The body chamber of their specimen, which begins at about 60 mm in diameter, is about 16 Accepted 17 18 440° long and ends with the aperture facing upward. The body chambers of HMG-2015 19 20 21 and HMG-2017 begin at about 60 mm and 68 mm in diameter, but their lengths are 22 23 24 about 300° and 210° respectively, suggesting that the last third and half of their 25 26 27 respective body chambers are not preserved. 28 29 30 Occurrence.—Santonian of Europe (France, Austria), the Middle East (Israel), 31 32 manuscript 33 southern Africa, Madagascar, southern USA (Mississippi) and Canadian Pacific Coast 34 35 36 (British Columbia), lower Campanian of Madagascar and South Africa, and lower 37 38 39 middle Campanian (Sphenoceramus orientalis Zone) of Hokkaido. 40 41 42 43 44 45 Discussion 46 47 48 49 50 51 It is plausibly assumed that Amapondella amapondense evolved from the early 52 53 54 Coniacian taxon Eubostrychoceras auriculatum (Collignon, 1965) of Madagascar 55 56 57 (Klinger and Kennedy, 1997), and then during Santonian time, extended its distribution 58 59 60

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1 2 3 4 5 6 to the Canadian Pacific Coast (British Columbia), southern USA, Europe, the Middle 7 8 9 East, southern Africa and Madagascar (e.g. Klinger, 1976; Summesberger, 1979, 1980; 10 11 12 Lewy, 1983; Kennedy and Cobban,1991; Kennedy et al., 1995; Haggart and Graham, 13 14 15 2018; Figure 5). However, by early Campanian time, its distribution had decreased to 16 Accepted 17 18 just southern Africa and Madagascar (Collignon, 1969; Klinger, 1976; Klinger et al., 19 20 21 2007; Figure 5), and then by the early middle Campanian, it had completely disappeared 22 23 24 from the middle southern latitudes, leaving only the Hokkaido occurrence of the present 25 26 27 study (Figure 5). 28 29 30 The Cretaceous Yezo Group in Hokkaido and Sakhalin, Far Eastern Russia yields 31 32 manuscript 33 numerous well-preserved fossils from various horizons (e.g. Matsumoto, 1954; 34 35 36 Vereshchagin, 1977). Nevertheless, in spite of extensive search efforts, specimens 37 38 39 assignable to Amapondella amapondense have not yet been discovered in Santonian to 40 41 42 lower Campanian deposits (e.g. Tanabe et al., 1977; Toshimitsu, 1988; Okamoto et al., 43 44 45 2003; Aiba et al., 2017), which strongly suggests that the species did not exist in the 46 47 48 Northwest Pacific during this time interval, and most likely extended its geographical 49 50 51 distribution from the middle southern latitudes into the Northwest Pacific region during 52 53 54 early middle Campanian time. 55 56 57 It is well known that some ammonoid taxa, e.g. Pseudophyllites Kossmat, 1895, 58 59 60

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1 2 3 4 5 6 Desmophyllites Spath, 1929, Pachydiscus Zittel, 1884, Saghalinites Wright and 7 8 9 Matsumoto, 1954, Metaplacenticeras Spath, 1926 and Didymoceras Hyatt, 1894 10 11 12 probably originated in other regions and extended their geographical distribution to the 13 14 15 Northwest Pacific region during late middle Campanian time (Shigeta, 1992; Shigeta et 16 Accepted manuscript 17 18 al., 2019). In contrast, some ammonoid species, e.g. Tetragonites popetensis Yabe, 19 20 21 1903 are widely distributed in the Upper Cretaceous successions in this particular 22 23 24 region (e.g. Shigeta, 1989; Maeda et al., 2005). As Shigeta et al. (2016) earlier pointed 25 26 27 out, the resultant late middle Campanian ammonoid faunas of the Northwest Pacific 28 29 30 region may have been supplemented by the addition of “foreign taxa” that migrated 31 32 33 from other regions into the existing indigenous ammonoid population. 34 35 36 Amapondella amapondense was probably one of these “foreign taxa” in the 37 38 39 Northwest Pacific region during early middle Campanian time. Although the reason for 40 41 42 the extinction of A. amapondense in other regions and its subsequent migration to the 43 44 45 Northwest Pacific region are unknown, the final geographic occurrence of the species in 46 47 48 Hokkaido suggests that global environmental changes likely had a significant influence 49 50 51 on ammonoid biogeography during early middle Campanian time as well as late middle 52 53 54 Campanian time. 55 56 57 A similar fluctuating pattern of geographical distribution is also known for the 58 59 60

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1 2 3 4 5 6 Albian–Cenomanian ammonoid Tanabeceras Shigeta et al., 2012 of the family 7 8 9 Gaudryceratidae Spath, 1927, which was widely distributed in California and the 10 11 12 Mediterranean area during early to middle Albian time, but disappeared from both areas, 13 14 15 and late Albian to Cenomanian members are known only from Hokkaido and Sakhalin 16 Accepted 17 18 (Shigeta et al., 2012). Iba and Sano (2007, 2008) discussed the existence of a vicariance 19 20 21 event which separated the North Pacific region from the Tethyan biotic realm during 22 23 24 Albian time, and then Shigeta et al. (2012) stated that this Albian vicariance event and 25 26 27 related chain episodes may have influenced the evolution of Tanabeceras. 28 29 30 It is unclear what type of global environmental changes affected ammonoid 31 32 manuscript 33 biogeography during middle Campanian time, but the changing pattern of geographical 34 35 36 distribution for various ammonoid taxa may provide an important key for understanding 37 38 39 the global environmental changes that occurred during middle Campanian time. 40 41 42 43 44 45 Acknowledgements 46 47 48 49 50 51 We thank Akihiro Misaki (Kitakyushu Museum of Natural History and Human 52 53 54 History, Kitakyushu), Herbert Klinger (Iziko South African Museum, Cape Town) and 55 56 57 Kazushige Tanabe (University Museum, The University of Tokyo) for valuable 58 59 60

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1 2 3 4 5 6 comments on the first draft. We are grateful to Katsuko Kubota (Sapporo, Hokkaido) 7 8 9 for donating the specimens and providing locality information. Thanks are extended to 10 11 12 Jim Jenks (West Jordan, Utah) for his helpful suggestions and improvement of the 13 14 15 English text. This study was financially supported by the National Museum of Nature 16 Accepted manuscript 17 18 and Science project, Chemical Stratigraphy and Dating as a Clue for Understanding the 19 20 21 History of the Earth and Life. 22 23 24 25 26 27 References 28 29 30 31 32 33 Aiba, D., Yamato, H., Kurihara, K. and Karasawa, T., 2017: A new species of 34 35 36 Eubostrychoceras (, Nostoceratidae) from the lower Campanian in 37 38 39 the northwestern Pacific realm. Paleontological Research, vol. 21, p. 255–264. 40 41 42 Arkell, W. J., 1957: Introduction to Mesozoic Ammonoidea. In, Arkell, W. J., Furnish, 43 44 45 W. M., Kummel, B., Miller, A. K., Moore, R. C., Schindewolf, O. H., 46 47 48 Sylvester-Bradley, P. C. and Wright, C. W. eds., Treatise on Invertebrate 49 50 51 Paleontology, Part L, 4, Cephalopoda, Ammonoidea, p. L81–129. 52 53 54 Geological Society of America, New York and University of Kansas Press, 55 56 57 Lawrence. 58 59 60

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1 2 3 4 5 6 Collignon, M., 1965: Atlas des fossiles caractéristiques de Madagascar (Ammonites). 7 8 9 Fascicle XIII (Coniacien), 88 p. Service Geologique, Tananarive. 10 11 12 Collignon, M., 1969: Atlas des fossiles caractéristiques de Madagascar (Ammonites). 13 14 15 Fascicle XV (Campanien inférieur), 216 p. Service Geologique, Tananarive. 16 Accepted manuscript 17 18 Gill, T., 1871: Arrangement of the families of mollusks. Smithsonian Miscellaneous 19 20 21 Collections, vol. 227, p. 1–49. 22 23 24 Haggart, J. W. and Graham, R., 2018: The crinoid Marsupites in the Upper Cretaceous 25 26 27 Nanaimo Group, British Columbia: Resolution of the Santonian–Campanian 28 29 30 boundary in the North Pacific Province. Cretaceous Research, vol. 87, p. 31 32 33 277–295. 34 35 36 Hoepen, E. C. N. van, 1921: Cretaceous Cephalopoda from Pondoland. Annals of the 37 38 39 Transvaal Museum, vol. 8, p. 1–48. 40 41 42 Hyatt, A., 1894: Phylogeny of an acquired characteristic. Proceedings of the American 43 44 45 Philosophical Society, vol. 32, p. 349–647. 46 47 48 Iba, Y. and Sano, S., 2007: Mid-Cretaceous step-wise demise of the carbonate platform 49 50 51 biota in the Northwest Pacific and establishment of the North Pacific biotic 52 53 54 province. Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 245, p. 55 56 57 462–482. 58 59 60

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1 2 3 4 5 6 ammonoids and inoceramids from the Ribira River area, Hokkaido, northern Japan. 7 8 9 National Museum of Nature and Science Monographs, no. 50, p. 1–139. 10 11 12 Shigeta, Y., Izukura, M., Nishimura, T. and Tsutsumi, Y., 2016: Middle and late 13 14 15 Campanian (Late Cretaceous) ammonoids from the Urakawa area, Hokkaido, 16 Accepted manuscript 17 18 northern Japan. Paleontological Research, vol. 20, p. 322–366. 19 20 21 Shigeta, Y. and Tsutsumi, Y., 2018: U–Pb age of the Sphenoceramus schmidti Zone 22 23 24 (middle Campanian, Cretaceous) in Hokkaido, northern Japan. Bulletin of the 25 26 27 National Museum of Nature and Science, Series C, vol. 44, p. 13–18. 28 29 30 Smith, A. G., Smith, D. G. and Funnel, B. M., 1994: Atlas of Mesozoic and Cenozoic 31 32 33 Coastlines, 99 p. Cambridge University Press, Cambridge. 34 35 36 Sokolov, D. V., 1914: Cretaceous Inoceramus of Russian Sakhalin. Trudy 37 38 39 Geologicheskogo komityeta, Novaya Seriya, vol. 83, p. 1–95. (in Russian and 40 41 42 German; original title translated) 43 44 45 Spath, L. F., 1926: On new ammonites from the English Chalk. Geological Magazine, 46 47 48 vol. 63, p. 77–83. 49 50 51 Spath, L. F., 1927: Revision of the fauna of Kachh (Cutch), part 1. 52 53 54 Memoirs of the Geological Survey of India, Palaeontologia Indica, New Series, 55 56 57 vol. 9, memoir 2, p. 1–71. 58 59 60

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1 2 3 4 5 6 Spath, L. F., 1929: Corrections of cephalopod nomenclature. Naturalist, vol. 871, p. 7 8 9 269–271. 10 11 12 Summesberger, H., 1979: Eine obersantone Ammonitenfauna aus dem Becken von 13 14 15 Gosau (Oberösterreich). Annalen des Naturhistorischen Museums in Wien, Band 16 Accepted manuscript 17 18 82, p. 109–176. 19 20 21 Summesberger, H., 1980: Neue Ammoniten aus der Sandkalkbank der 22 23 24 Hochmoosschichten (Obersanton: Gosau, Österreich). Annalen des 25 26 27 Naturhistorischen Museums in Wien, Band 83, p. 275–283. 28 29 30 Takahashi, K. and Suzuki, M., 1978: Explanatory Text of the Geological Map of Japan, 31 32 33 Scale 1:50,000 Iwachishi (Sapporo-45), 46 p. Geological Survey of Hokkaido, 34 35 36 Sapporo. (in Japanese with English abstract) 37 38 39 Takahashi, K. and Suzuki, M., 1986: Explanatory Text of the Geological Map of Japan, 40 41 42 Scale 1:50,000 Hidaka (Sapporo-34), 44 p. Geological Survey of Hokkaido, 43 44 45 Sapporo. (in Japanese with English abstract) 46 47 48 Tanabe, K., Hirano, H., Matsumoto, T. and Miyata, Y., 1977: Stratigraphy of the Upper 49 50 51 Cretaceous deposits in the Obira area, northwestern Hokkaido. Science Reports, 52 53 54 Department of Geology, Kyushu University, vol. 12, p. 181–202. (in Japanese 55 56 57 with English abstract) 58 59 60

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1 2 3 4 5 6 Toshimitsu, S., 1988: Biostratigraphy of the Upper Cretaceous Santonian stage in 7 8 9 northwestern Hokkaido. Memoirs of the Faculty of Science, Kyushu University, 10 11 12 Series D, Geology, vol. 26, p. 125–192. 13 14 15 Vereschagin, V. N., 1977: The Cretaceous System of Far East. Trudy Vsesoyunogo 16 Accepted manuscript 17 18 Nauchno-Issledovatel’skogo Geologicheskogo Instituta (VSEGEI), New Series, 19 20 21 vol. 245, p. 1–207. (in Russian; original title translated) 22 23 24 Wada, N., Takahashi, K., Watanabe, J. and Kanie, Y., 1992: Explanatory Text of the 25 26 27 Geological Map of Japan, Scale 1:50,000 Mitsuishi (Kushiro-65), 73 p. 28 29 30 Geological Survey of Hokkaido, Sapporo. (in Japanese with English abstract) 31 32 33 Wiedmann, J., 1966: Stammesgeschichte und System der posttriadischen Ammonoideen, 34 35 36 ein Überblick (2. Teil). Neues Jahrbuch für Geologie und Paläontologie, 37 38 39 Abhandlungen, Band 127, p. 13–81. 40 41 42 Wright, C. W., Calloman, J. H. and Howarth, M. K., 1996: Treatise on Invertebrate 43 44 45 Paleontology, Part L, Mollusca 4, Revised, vol. 4, Cretaceous Ammonoidea, 362 p. 46 47 48 Geological Society of America, Boulder and University of Kansas Press, 49 50 51 Lawrence. 52 53 54 Wright, C. W. and Matsumoto, T., 1954: Some doubtful Cretaceous ammonites genera 55 56 57 from Japan and Saghalien. Memoirs of the Faculty of Science, Kyushu University, 58 59 60

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1 2 3 4 5 6 Series D, Geology, vol. 4, p. 107–134. 7 8 9 Yabe, H., 1903: Cretaceous Cephalopoda from the Hokkaido. Part 1: Lytoceras, 10 11 12 Gaudryceras, and Tetragonites. Journal of the College of Science, Imperial 13 14 15 University of Tokyo, vol. 18, p. 1–55. 16 Accepted manuscript 17 18 Yoshida, T., Matsuno, K., Satoh, H. and Yamaguchi, S., 1959: Explanatory Text of the 19 20 21 Geological Map of Japan, Scale 1:50,000 Biu (Sapporo-56), 55 p. Geological 22 23 24 Survey of Hokkaido, Sapporo. (in Japanese with English abstract) 25 26 27 Zittel, K. A., 1884: Cephalopoda. In, Zittel, K. A. ed., Handbuch der Palaeontologie, 28 29 30 Band 1, Abt. 2, Lief 3, p. 329–522. Oldenbourg, Munich and Leipzig. 31 32 33 34 35 36 37 38 39 Author contributions 40 41 42 M. I. collected fossils and contributed to the geological aspect of the study. Y. S. 43 44 45 conduced taxonomic study. Both authors contributed to the writing of the paper. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 7 8 9 10 11 12 Figure caption 13 14 15 16 Accepted manuscript 17 18 Figure 1. Index map showing distribution of the Yezo Group (black area) in Hokkaido 19 20 21 (A) and collection localities of Amapondella amapondense specimens in the Hidaka, 22 23 24 Biratori and Urakawa areas (indicated by stars, B, C). 25 26 27 28 29 30 Figure 2. Amapondella amapondense (van Hoepen, 1921). A–F, HMG-2014, from 31 32 33 outcrop of the Chinomigawa Formation exposed along the middle course of the 34 35 36 Soushubetsu River in the Biratori area. A, B, apical views; C, D, lateral views; E, F, 37 38 39 basal views; G–I, HMG-2016, from a float calcareous concretion found along the 40 41 42 southern coast of Ikantai in the Urakawa area; G, apical view; H, basal view; I, lateral 43 44 45 view. Arrowheads indicate position of last septum. 46 47 48 49 50 51 Figure 3. Amapondella amapondense (van Hoepen, 1921), HMG-2015, from a float 52 53 54 calcareous concretion found in the upper course of Pankeushappu River in the Hidaka 55 56 57 area. A, B, apical views; C, D, lateral views; E, F, basal views. Arrowheads indicate 58 59 60

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1 2 3 4 5 6 position of last septum. 7 8 9 10 11 12 Figure 4. Amapondella amapondense (van Hoepen, 1921), HMG-2017, from a float 13 14 15 calcareous concretion found along the southern coast of Ikantai in the Urakawa area. A, 16 Accepted manuscript 17 18 apical views; B, oblique apical view rotated 45° from A; C, lateral view rotated 90° 19 20 21 from A; D, basal view; E, lateral view rotated 90° from D. Arrowheads indicate position 22 23 24 of last septum. 25 26 27 28 29 30 Figure 5. Paleogeographical (A) and stratigraphical (B) distribution of Amapondella 31 32 33 amapondense (van Hoepen, 1921) during Santonian to middle Campanian time. 34 35 36 Paleomap from Smith et al. (1994). 1, British Columbia (Haggart and Graham, 2018); 2, 37 38 39 Mississippi (Kennedy and Cobban, 1991); 3, France (Kennedy et al., 1995); 4, Austria 40 41 42 (e.g. Summesberger, 1979); 5, Israel (Lewy, 1983); 6, South Africa (e.g. Klinger and 43 44 45 Kennedy, 2003); 7, Madagascar (e.g. Klinger et al., 2007); 8, Hokkaido (this study). 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 Accepted 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 manuscript 31 32 33 34 35 36 37 38 39 40 41 42 43 Figure 1. Index map showing distribution of the Yezo Group (black area) in Hokkaido (A) and collection 44 localities of Amapondella amapondense specimens in the Hidaka, Biratori and Urakawa areas (indicated by 45 stars, B, C). 46 165x187mm (300 x 300 DPI) 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Page 27 of 30 Paleontological Research

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Accepted 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 manuscript 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Figure 2. Amapondella amapondense (van Hoepen, 1921). A–F, HMG-2014, from outcrop of the 46 Chinomigawa Formation exposed along the middle course of the Soushubetsu River in the Biratori area. A, 47 B, apical views; C, D, lateral views; E, F, basal views; G–I, HMG-2016, from a float calcareous concretion found along the southern coast of Ikantai in the Urakawa area; G, apical view; H, basal view; I, lateral view. 48 Arrowheads indicate position of last septum. 49 50 214x279mm (300 x 300 DPI) 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research Page 28 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Accepted 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 manuscript 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Figure 3. Amapondella amapondense (van Hoepen, 1921), HMG-2015, from a float calcareous concretion 46 found in the upper course of Pankeushappu River in the Hidaka area. A, B, apical views; C, D, lateral views; 47 E, F, basal views. Arrowheads indicate position of last septum. 48 214x279mm (300 x 300 DPI) 49 50 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Page 29 of 30 Paleontological Research

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Accepted 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 manuscript 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Figure 4. Amapondella amapondense (van Hoepen, 1921), HMG-2017, from a float calcareous concretion 46 found along the southern coast of Ikantai in the Urakawa area. A, apical views; B, oblique apical view 47 rotated 45° from A; C, lateral view rotated 90° from A; D, basal view; E, lateral view rotated 90° from D. Arrowheads indicate position of last septum. 48 49 214x279mm (300 x 300 DPI) 50 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan Paleontological Research Page 30 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Accepted manuscript 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Figure 5. Paleogeographical (A) and stratigraphical (B) distribution of Amapondella amapondense (van 34 Hoepen, 1921) during Santonian to middle Campanian time. Paleomap from Smith et al. (1994). 1, British 35 Columbia (Haggart and Graham, 2018); 2, Mississippi (Kennedy and Cobban, 1991); 3, France (Kennedy et 36 al., 1995); 4, Austria (e.g. Summesberger, 1979); 5, Israel (Lewy, 1983); 6, South Africa (e.g. Klinger and Kennedy, 2003); 7, Madagascar (e.g. Klinger et al., 2007); 8, Hokkaido (this study). 37 38 115x94mm (300 x 300 DPI) 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Paleontological Society of Japan