Two New Gastropods from the Late Pliocene Omma-Manganji Fauna In

Two New Gastropods from the Late Pliocene Omma-Manganji Fauna in the Japan Sea Borderland of Honshu, Japan Author: Kazutaka Amano Source: Paleontological Research, 23(2) : 85-94 Published By: Palaeontological Society of Japan

URL: https://doi.org/10.2517/2018PR011

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Downloaded From: https://bioone.org/journals/Paleontological-Research on 10 Apr 2019 Terms of Use: https://bioone.org/terms-of-use Access provided by The Palaeontological Society of Japan Paleontological Research, vol. 23, no. Gastropods2, pp. 85–94, Aprilfrom 1, late 2019 Pliocene Omma-Manganji fauna 85 © by the Palaeontological Society of Japan doi:10.2517/2018PR011

Two new gastropods from the late Pliocene Omma- Manganji fauna in the Japan Sea borderland of Honshu, Japan

KAZUTAKA AMANO

Department of Geoscience, Joetsu University of Education, Joetsu, Niigata 943-8512, Japan (e-mail: [email protected])

Received February 26, 2018; Revised manuscript accepted June 2, 2018

Abstract. A new genus and species of the gastropod family Capulidae, Vermeijia japonica, is described from the upper Pliocene Kuwae Formation in Niigata Prefecture and the lowermost part of the Sasaoka Formation in Akita Prefecture, Japan. This genus is similar to the boreal genus Ariadnaria although it was collected in association with several warm-water species. In another gastropod family, Nassariidae, Cyllene satoi is a new species from the upper Pliocene Tentokuji Formation in Akita Prefecture. Nine warm-water taxa in the Omma- Manganji fauna, including Cyllene, no longer live in the Japan Sea, except for its westernmost part. They suggest that the Tsushima Current had a higher SST during the late Pliocene than at present. Vermeijia is the fourth extinct genus of the Omma-Manganji fauna, but it disappeared in the Japan Sea by Datum A (2.75 Ma), earlier than the other three genera, which became extinct by the end of the early Pleistocene.

Key words: Gastropoda, Japan Sea, late Pliocene, Omma-Manganji fauna, paleotemperature

Introduction ermost part of the Sasaoka Formation. One of them is the capulid Vermeijia japonica gen. and sp. nov. and the During the early Pliocene to early Pleistocene, many other is Cyllene satoi sp. nov. Both genera were collected endemic species of mollusks originated in the semi- from assemblages that included warm-water species. closed Japan Sea (Chinzei, 1978). The fauna is known Among them, Cyllene is now widely distributed in the as the Omma-Manganji fauna (Otuka, 1939) and the tax- Indo-Pacific region, but is confined to the westernmost onomy of its mollusks has been studied by many authors part of the Japan Sea (Higo et al., 1999). In this paper, I (Kaseno and Matsuura, 1965; Ogasawara, 1977, 1986; describe these gastropods and discuss their biogeographi- Kitamura and Kondo, 1990; Amano, 2001, 2004, 2007). cal significance. The Omma-Manganji fauna mainly consists of shallow cold-water species as well as endemic extinct species. Material and methods However, it contains some warm-water species, indicat- ing inflow of the Tsushima warm current (e.g. Ogasawara, One specimen of Vermeijia japonica gen. and sp. nov. 1986). During the late Pliocene, many kinds of shallow was recovered from Loc. 2 by Amano et al. (2000a) (Loc. warm-water taxa were recovered from the upper Pliocene 3 in Figure 1) in the upper Pliocene Kuwae Formation deposits along the Japan Sea, from the Tentokuji Forma- in Niigata Prefecture and another one from Loc. TH1 by tion and the lowermost part of the Sasaoka Formation Amano et al. (2011) (Loc. 1 in Figure 1) in the upper in Akita Prefecture, the Kuwae and Shitoka formations Pliocene part of the Sasaoka Formation in Akita Pre- in Niigata Prefecture, and the Mita and Zuwaka forma- fecture. Based on the associated molluscan fossils, both tions in Toyama Prefecture (Amano et al., 2000a, b, 2008, formations were deposited in lower sublittoral depths. 2009, 2011, 2012). Thus, in the late Pliocene, the warm However, in the case of the Kuwae Formation, the fossils Tsushima current flowed into the Japan Sea and reached reveal that the occurrence is allochthonous, in contrast as far north as Akita Prefecture, northern Honshu. with their autochthonous occurrence in the Sasaoka For- Two new gastropods have been collected from the mation (see Amano et al., 2000a, 2011). The new genus Tentokuji Formation, the Kuwae Formation and the low- possibly lived in water shallower than the lower sublit-

the new taxa are stored at the University Museum of the University of Tokyo. Abbreviations of institutions: IGPS, Institute of Geology and Paleontology, Faculty of Sci- ence, Tohoku University; JUE, Joetsu University of Edu- cation; NMNS, National Museum of Nature and Science, Tsukuba; UMUT, University Museum of the University of Tokyo.

Systematic descriptions

Family Capulidae Fleming, 1822 Genus Vermeijia gen. nov.

Etymology.—The present new genus is named for Geerat J. Vermeij (University of California at Davis) who has contributed extensively to the taxonomy of gastropods. Type species.—Vermeijia japonica sp. nov. Diagnosis.—Shell moderate-sized, rather thin, globose; spire very low; surface of spire whorls cancellate with a few spiral cords and fine axial ribs; surface of last whorl sculptured with spiral costae; aperture very wide, Figure 1. Localities of the fossils herein treated. posterior end located above deep suture between last and penultimate whorls; inner lip covered by callus with one weak fold in its anterior part; outer lip thin; umbilicus toral zone. narrow, with weak fasciole; anterior canal very short and Six specimens of Cyllene satoi sp. nov. were collected narrow. from Loc. 21 by Amano et al. (2000b) (Loc. 2 in Figure 1) Included species.—Other than the type species, Trichot- in the upper Pliocene Tentokuji Formation in Akita Pre- ropis planicostata Yokoyama, 1920 is included in this fecture. The occurrence at this locality is allochthonous. genus. Trichotropis planicostata was originally described Many shallow-water gastropods were carried down to by Yokoyama (1920) from the lower Pleistocene Koshiba upper bathyal or lower sublittoral depths (Amano et al., Formation in Kanagawa Prefecture, based on one young 2000b). specimen. Baba (1990) described and illustrated the adult For proposing these new taxa, the following speci- specimen having a rapidly expanding last whorl from the mens were also examined; Trichotropis planicostata lower Pleistocene Umegase Formation in Chiba Prefec- Yokoyama, UMUT CM 20192 (holotype; Loc. Koshiba, ture (Figure 2.3). Nemoto and O’Hara (2005) illustrated Kanagawa Prefecture; the lower Pleistocene Koshiba one specimen which has a rapidly expanding last whorl Formation), NMNS PM25264 (Loc. Kamataki, Kimitsu as T. insignis (Middendorff) from the lower Pleistocene City, Chiba Prefecture; the middle Pleistocene Ichijuku Tomioka Formation in Fukushima Prefecture. Adding Formation), NMNS PM28601 (collected by Baba, 1990 one specimen (Figure 2.4) from the middle Pleistocene from Higashi-Hikasa, Kimitsu City, Chiba Prefecture; the Ichijuku Formation in Chiba Prefecture and stored at the lower Pleistocene Kiwada Formation); Cyllene pulchella National Museum of Nature and Science, Tsukuba, this Adams and Reeve, IGPS no. 55136 (Loc. Ananai, Kochi species has been recorded from lower to middle Pleisto- Prefecture; the lowest Pleistocene Ananai Formation); cene deposits on the Pacific side of central Honshu. Cyllene lugubris Adams and Reeve, IGPS nos. 53912, Remarks.—The present genus has a unique and enig- 53913, 53914, 53915, 53916, 53917, 53918, 53919 (the matic form. However, despite lacking the protoconch, lower Pleistocene Byoritsu Beds in Taiwan); Cyllene the close similarity to species of Ariadnaria Habe, 1961, rubulolineata Sowerby, JUE no. 16068 (Loc. off Minabe, Neoiphinoe Habe, 1978, and Trichotropis Broderip and Wakayama Prefecture, 80–100 m in depth). Sowerby, 1829 demonstrates that it should be classified I measured and counted the following characters of the in Capulidae Fleming, 1822. fossils: shell height, height of the spire, maximum diam- Ariadnaria is the most similar to Vermeijia gen. nov. It eter, and the number of axial ribs and spiral cords on the is similar in having a low spire, a large last whorl, distinct penultimate and last whorls. All specimens representing cancellate sculpture which is observed in the early whorls

Figure 2. Vermeijia japonica gen. et sp. nov. and V. planicostata (Yokoyama, 1920). 1, 2, Vermeijia japonica gen. et sp. nov.; 1a, b, paratype, UMUT CM 32796; 1a, internal mold; 1b, outer cast (silicone rubber), Loc. 1; 2a–e, holotype, UMUT CM 32795; 2a, apertural view; 2b, apical view; 2c, enlargement of apical view; 2d, enlargement of early whorls from abapertural side; 2e, abapertural view, Loc. 3; 3, 4, Ver- meijia planicostata (Yokoyama, 1920); 3, NMNS PM28601 abapertural view; 4, NMNS PM25264, apertural view. All scale bars show 5 mm.

of the new genus, some strong spiral costae, a fold on Description.—Shell moderate in size for Capulidae, up the inner lip, a narrow umbilicus, a narrow fasciole and to 27.1 mm in height, rather thin, fragile, globose (maxi- a short siphonal canal. However, the thin shell, rapidly mum diameter = 26.3 mm). Teleoconch whorls four, with expanding last whorl, and deep suture between the pen- large last whorl and very low spire (spire height/shell ultimate and last whorls of the present new genus easily height = 0.13); spire whorls with coiling axis at slight enable us to separate the two genera. angle to that of last whorl; protoconch not preserved. First Neoiphinoe is another similar genus to the present whorl sculptured with two strong spiral cords with dis- new genus in having a rather low spire, a large last whorl tinct growth lines; second whorl sculptured with one weak and some strong spiral costae in some species such as N. and two strong spiral cords, uppermost weakest, and 19 kryoyeri (Philippi, 1849) illustrated by Kantor and Sysoev fine axial ribs forming cancellate sculpture; penultimate (2006). However, it differs from the new genus by having whorl sculptured with three spiral cords with fourteen a wide and distinct fasciole, a lower spire, a larger body fine axial ribs forming nodes at their intersections, lower- whorl, and a very weak fold at the inner lip. most cord buried below deep suture between penultimate Trichotropis is another similar genus to the present new and last whorls; last whorl sculptured with six sharp, nar- genus. It shares its strong spiral costae, rather deep suture, row spiral costae with interspaces each crenulated wider one weak fold on the inner lip, narrow fasciole and short and flatter than one costa, interspaces crossed by very siphonal canal. However, Trichotropis has a higher spire weak, fine axial ribs and a few very low secondary spiral and a smaller aperture than in Vermeijia gen. nov. cords. Suture between last and penultimate whorls very deep and wide, but other sutures shallower. Aperture very Vermeijia japonica sp. nov. wide, semi-lunular; posterior end forming vertical angle Figures 2.1, 2.2 with inner lip and located above suture between last and penultimate whorls; most basal part of inner lip slightly Ariadnaria insignis (Middendorff). Ogasawara et al., 1986, pl. 37, fig. broken but mostly covered by thin callus, with one weak 3a, b. fold on its anterior part; outer lip thin between triangular cross-sections of exterior spiral costae; false umbilicus Etymology.—The present new species is named for the very narrow, moderately deep, with weak fasciole; sipho- country of Japan. nal canal weakly defined, very short and narrow. Type specimens.—Holotype, UMUT CM 32795; para- Remarks.—Ogasawara et al. (1986) illustrated a small type, UMUT CM 32796. specimen of Ariadnaria insignis (Middendorff) from the Type Locality.—River bank at 1.3 km upstream along Sasaoka Formation at Loc. S15, about 3 km southeast the Koide River, Shibata City, Niigata Prefecture (Loc. from Loc. TH1 by Amano et al. (2011) (Loc. 1 in Fig- 3 in Figure 1 = Loc. 2 of Amano et al., 2000a); Kuwae ure 1). However, the illustrated specimen has a rapidly Formation. expanding last whorl, three spiral cords with fine axial Material.—Two specimens consisting of the holotype ribs on the penultimate whorl, and six spiral costae on the and the paratype. The paratype specimen was collected last whorl. These characteristics are shared with Vermei- from the Sasaoka Formation at 2 km upstream along the jia japonica sp. nov. Ogurosawa River, Akita City in Akita Prefecture (Loc. 1 Vermeijia planicostata (Yokoyama, 1920) differs from in Figure 1 = Loc. TH1 of Amano et al., 2011). V. japonica sp. nov. by having a slightly smaller shell Dimensions.—Holotype, UMUT CM 32795, shell (maximum height = 21.2 mm+), spire whorls coiled at height = 27.1 mm, maximum diameter = 26.3 mm, the same angle to the last whorl, more numerous (4) spiral height of spire = 3.6 mm; paratype, UMUT CM 32796, cords on the penultimate whorl, lower and more numer- shell height = 19.2 mm, maximum diameter = 17.3 mm, ous spiral cords (8 to 13) on the last whorl which become height of spire = 4.0 mm (a natural internal mold, and a obscure above the shoulder. silicone rubber cast of the exterior). Ariadnaria hirsuta (Golikov and Gulbin, 1978) living Diagnosis.—Shell moderate in size for Capulidae, in the middle Kurile Islands (5–285 m in depth; Golikov rather thin and globose; spire very low, three spire whorls et al., 2001; Kantor and Sysoev, 2006) is also similar to coiled at slight angle to last whorl; surface of penultimate the present new species. It has a large last whorl, spire whorl sculptured with three spiral cords and fourteen fine whorls coiled at a slight angle to the last whorl, and seven axial ribs forming nodes at their intersections; surface of (12 by the original description) strong spiral costae with last whorl sculptured with six sharp spiral costae, each growth lines on the last whorl. Ariadnaria hirsuta differs narrower than an interspace; aperture very wide, posterior from Vermeijia japonica sp. nov. in its much smaller size end located highly above suture between last and penul- (9.8 mm in shell height) and smaller aperture. timate whorls. Ariadnaria insignis (Middendorff, 1848) is another sim-

ilar species living in the northern Japan Sea, the Okhotsk Dimensions.—Holotype, UMUT CM 32797, shell Sea, the Kurile Islands and the Bering Sea (0–100 m in height = 12.8 mm, maximum diameter = 7.5 mm, height depth; Golikov et al., 2001). It has a low spire, a large of spire = 2.1 mm; paratype, UMUT CM 32798, shell last whorl and a large aperture. However, the surface of height = 12.6 mm, maximum diameter = 7.9 mm, height the last whorl of A. insignis is covered with cancellate of spire = 1.8 mm. sculpture, which is observed in younger whorls in Ver- Diagnosis.—Small species of Cyllene with low spire, meijia japonica sp. nov. Moreover, the more numerous well inflated last whorl sculptured with 14–18 low spiral and lower spiral cords of A. insignis enable us to separate cords and 20–22 low axial ribs. Outer lip sculptured with it from the present new species. 11–12 crenulations. Fasciole thick, with 5–11 wrinkles. Neoiphinoe kroyeri (Philippi, 1849) is yet another sim- Description.—Shell small, up to 12.8 mm in height, ilar species living in the southern Okhotsk Sea, Bering consisting of four teleoconch whorls, ovately conical, well Sea, Barents, Kara and Laptev seas (22–150 m in depth; inflated (maximum diameter/shell height = 0.59–0.63), Kantor and Sysoev, 2006). It has a low spire, a large body spire low, last whorl large (height of spire/shell height = whorl and some strong costae crossed by distinct growth 0.14–0.16); protoconch not preserved. Suture deep; sub- lines. However, N. kroyeri has a smaller body whorl with sutural cord relatively wide, almost flat, bounded by mod- a lower spire, a wider and distinct fasciole, a narrow pos- erately deep groove, then by three shallower grooves and terior sinus of aperture, a shallower suture between the ridges. Penultimate whorl ornamented with six to eight body and the penultimate whorls and a weaker fold at the fine spiral cords including flat subsutural cord divided by inner lip. deep grooves, and with 20–22 rounded, straight axial ribs Torellia pacifica Okutani, 1980 also has a low spire and forming nodes at intersections with spiral cords. Spiral strong costae on the last whorl. However, T. pacifica has cords on last whorl two above deep subsutural groove, regularly coiled whorls, a smaller aperture and a wider five below this groove and 11 on basal part. Last whorl siphonal canal than the present new species. also sculptured with 23–32 weak axial ribs near suture Stratigraphic and geographic distribution.—Upper between penultimate and last whorls. Aperture lenticu- Pliocene: Kuwae Formation in Niigata Prefecture and lar; anal sinus slit-like; inner lip covered with thin callus lowermost part of Sasaoka Formation in Akita Prefecture. on posterior half but becoming thick towards basal part, with five to 11 folds; outer lip rather thick, with 11–12 Family Nassariidae Iredale, 1916 short transverse ridges on interior; siphonal canal short, Subfamily Cylleninae Bellardi, 1882 twisted; fasciole rather large, separated by a sharp, nar- Genus Cyllene Gray in Griffith and Pidgeon, 1834 row ridge and deep groove from base of last whorl. Remarks.—Amano et al. (2000b) illustrated this new Type species.—Cyllene owenii Gray in Griffith and species as Cyllene aff. pulchella with the earliest Pleisto- Pidgeon, 1834. cene species from the Ananai Formation in Kochi Prefec- ture. This species was listed as C. pulchella Adams and Cyllene satoi sp. nov. Reeve by Nomura (1937) and described as Strigitella cf. Figures 2.1–2.3 decurtata Reeve by Okumura and Takei (1993). How- ever, the Ananai species (Amano et al., 2000b, pl. 1, fig. Cyllene aff. pulchella Adams and Reeve. Amano et al., 2000b, pl. 1, 10, 11; IGPS 55136) can be identified as C. gracilenta figs. 4, 9. non Cyllene aff. pulchella Adams and Reeve. Amano et al., 2000b, pl. (Yokoyama, 1928) because it has a smooth surface of the 1, figs. 10, 11. last whorl without any spiral grooves near the suture or on the basal part. Exceptionally one small specimen from the Etymology.—The present new species is named for Ananai Formation (Figure 2.3) has ten axial ribs, which is Tokiyuki Sato (Akita University), who contributed to the similar to the holotype of C. gracilenta. age assignment of the Plio-Pleistocene formations in the Cyllene gracilenta was proposed for the specimen from Japan Sea area by calcareous nannofossils. the Pliocene? Lower Byoritsu Bed in Taiwan as a species Type specimens.—Holotype, UMUT CM 32797; para- of Cassis by Yokoyama (1928). Later, it was described type, UMUT CM 32798. from the Pliocene Yonabaru Clay in Okinawa Prefecture Type Locality.—Riverside cliff at 0.5 km downstream by MacNeil (1960). He also synonymized C. lugubris along the Yodo River, Kyowa-Funaoka-Awasegai, Daisen Adams and Reeve, 1850 described by Nomura (1935) City, Akita Prefecture (Loc. 2 in Figure 1 = Loc. 21 of from the Byoritsu Beds in Taiwan with C. gracilenta. Hu Amano et al., 2000b). (1992) described C. lugubris from the Pleistocene Tongx- Material.—Six specimens treated here were collected iao Formation in Miaoli (= Byoritsu) Province, Taiwan. only from the type locality. This species can be classified into C. glacilenta, judging

Figure 3. Cyllene satoi sp. nov. and C. glacilenta (Yokoyama, 1928). 1, 2, Cyllene satoi sp. nov.; 1a, b, holotype, UMUT CM 32797; 1a, apertural view; 1b, abapertural view; 2a–c, paratype, UMUT CM 32798; 2a, apertural view; 2b, abapertural view; 2c, enlargement of spire and upper part of the last whorl, Loc. 2; 3, 4, Cyllene glacilenta (Yokoyama, 1928); 3a, b, IGPS no. 55136-1; 3a, apertural view; 3b, abapertural view; 4a–c, IGPS no. 55136-2; 4a, apertural view; 4b, abapertural view; 4c, enlargement of spire and upper part of the last whorl, Loc. Ananai, Kochi Prefecture. All scale bars show 5 mm.

from its shell surface sculpture. sp. nov. has eighteen distinct spiral cords on the whole Cyllene satoi sp. nov. is most similar to this extinct surface of the last whorl while C. gracilenta has a smooth species C. gracilenta in having a similar shell outline. C. and shiny surface in the middle part of the last whorl. satoi sp. nov. can be distinguished from C. gracilenta by The Recent species Cyllene rubrolineata Sowerby, 1870 having numerous axial ribs near the suture between the resembles the present new species. Cernohorsky (1984) penultimate and the last whorls (23–32 in C. satoi; 0–15 illustrated the holotype of this species and described it in C. gracilenta; Figures 3.2c, 3.4c). Moreover, C. satoi as distributed only in Taiwan. However, Tsuchiya (2017)

Table 1. Distribution of the gastropod genera, subgenera or species not now living in the main part of the Japan Sea. *, extinct species; °, extant species; 1), northern limit of the distribution of modern species in the Japan Sea (NLDJ). Yamaguchi is the westernmost part of the Japan Sea side of Honshu. Parentheses mean the northernmost region of each taxon. 2), shallowest depth of each taxon. The data on the distribution of the extant species are based on Higo et al. (1999). Locality numbers in this table correspond to those in Figure 1.

Locality 1 2 3 4 5 1) Shallowest Formation Lowest NLDJ 2) Tentokuji Kuwae Shitoka Mita depth (m) Species Sasaoka Conus sp. + + Yamaguchi 0

Mammilla spp. + + + Yamaguchi 10

Cyllene satoi sp. nov.* + Yamaguchi 0

Scalptia kurodai* + Yamaguchi 0

Neritina (Vittina) aff. parallela + (Amami Is.) 0

Calyptraea yokoyamai° + (E. China Sea) 20

Chicoreus (Triplex) totomiensis* + (E. China Sea) 0

Mitra (Mitra) cf. chinensis + (E. China Sea) 0

Punctacteon kajiyamai° + (Cape Ashizuri) 0

Amano et al. Amano et al. Amano et al. Amano et al. Amano et al. Reference (2011) (2000b) (2000a) (2009) (2008)

recorded this species from Sagami Bay, central Honshu about 4 Ma (Amano et al., 2008). As noted above, this and southward. Fifteen specimens of C. rubrolineata at current reached as far north as Akita Prefecture, northern hand from off Minabe, Wakayama Prefecture, southwest Honshu, during the late Pliocene, while it reaches north- Honshu (80–100 m in depth) have seven, less inflated ern Hokkaido today. The reason why the influence of the whorls (maximum diameter/shell height = 0.48–0.59, current was weaker than now during the warmer period of rarely to 0.61 in C. rubrolineata), a higher spire (height of the late Pliocene is possibly because the current reached a spire/shell height = 0.16–0.24), and less numerous axial lesser depth than at present (Kitamura and Kimoto, 2006). ribs on the last whorl (commonly 17). Some warm-water gastropod genera and species not liv- Cyllene pulchella Adams and Reeve, 1850 is now living in the main part of the Japan Sea have been recorded ing in the Red Sea to India, Japan and the New Hebrides (Amano, 2007) from the Omma-Manganji fauna. Table 1 (Cernohorsky, 1984). This species is different from C. summarizes these taxa, including Cyllene satoi sp. nov. satoi sp. nov. by having a smooth and shiny last whorl. Other than Mammilla spp. (10 m depth) and Calyptraea Stratigraphic and geographic distribution.—Upper yokoyamai (20 m depth), the shallowest depth inhabited Pliocene: Tentokuji Formation in Akita Prefecture. by these taxa is the intertidal zone (Higo et al., 1999). Among them, Cyllene herein treated is one of the typi- Discussion cal species now living in the tropical Indo-Pacific, West Africa and S.E. Australia (Cernohorsky, 1984). Based During the mid-Pliocene (3.256–3.025 Ma), the sur- on Higo et al. (1999), Conus, Mammilla, Cyllene and face temperature was 2.7–4.0°C higher than today and Scalptia are now distributed as far north as Yamaguchi sea level was 10–30 m higher than today during intergla- Prefecture, in the westernmost part of Honshu. Fossils cial periods (Dwyer and Chandler, 2009; Haywood et al., of these genera have been recorded from Akita Prefec- 2013, 2016). The shallow warm-water Tsushima Current ture, northernmost Honshu. A relatively high winter SST flowed into the Japan Sea during interglacial periods from is essential for the warm-water species’ survival. The 3.5 to 1.7 Ma (Kitamura and Kimoto, 2006; Gallagher average SST in January (1981–2010) is about 4.0°C et al., 2015). Based on calcareous nannofossils and higher in Yamaguchi than in Akita (Japan Meteorologi- tephrochronology, it has been elucidated that the warm cal Agency; http://www.data.jma.go.jp/kaiyou/data/db/ Tsushima Current began to flow into the Japan Sea since kaikyo/jun/sst_HQ.html?areano=3). A brackish-water

dweller, Neritina (Vittina), collected from the Kuwae V. japonica and survived into the late Pleistocene on the Formation in Niigata Prefecture, central Honshu, is now Pacific side of central Honshu like Mizuhopecten tokyo- living southward from Amami-Ohshima. However, this ensis (Tokunaga, 1906) (see Amano, 2007). genus is not suitable for estimating the paleotemperature because its habitat is affected also by salinity, not only Acknowledgments by temperature. Calyptraea yokoyamai, Chicoreus (Tri- plex) and Mitra (Mitra) also have been collected from I am very grateful to Alan Beu (GNS Science) for his the Kuwae and Shitoka formations in Niigata. These are critical reading of this manuscript. I thank two anonymous now not living in the Japan Sea, but do still live in the reviewers for their critical comments to improve the man- East China Sea off western Kyushu. The average SST in uscript. I also thank T. Sasaki (University Museum, The January (1981–2010) is about 4°C lower in Niigata than University of Tokyo), H. Nishi and J. Nemoto (Tohoku in northwestern Kyushu (Japan Meteorological Agency; University, Sendai), T. Haga (National Museum of Nature http://www.data.jma.go.jp/kaiyou/data/db/kaikyo/jun/ and Science, Tsukuba), and N. Nemoto (Hirono Town) sst_HQ.html?areano=3). Punctacteon kajiyamai, also for their help in examining the fossil specimens. This collected from the Shitoka Formation, is not suitable for study was partly supported by a Grant-in-aid for Scien- estimating the paleotemperature because it is a modern tific Research of the Japan Society for the Promotion of endemic species in southeastern Shikoku. These estima- Science (C, 17K05691, 2017–2019). tions of SST, about 4.0°C higher than the present day, are nearly concordant with the global warming during References the late Pliocene. As noted above, the Tsushima Current Adams, A. and Reeve, A. L., 1850: Mollusca. In, Adams, A. ed., The at the time was thinner but warmer. If global warming Zoology of the Voyage of H.M.S. Samarang; under the Command continues, it will allow these taxa to enter the Japan Sea of Captain Sir Edward Belcher, during the Years 1843–1846, Part again. 2, p. 25–44. Reeve and Benham, London. Vermeijia most closely resembles the boreal genus Ari- Amano, K., 2001: Pliocene molluscan fauna of Japan Sea borderland adnaria. As described above, the young shell of Vermei- and the paleoceanographic conditions. Biological Science (Tokyo), vol. 53, p. 178–184. (in Japanese) jia looks like Ariadnaria insignis. Thus, Ogasawara et al. Amano, K., 2004: Biogeography and the Pleistocene extinction of neo- (1986) and Nemoto and O’Hara (2005) respectively mis- gastropods in the Japan Sea. Palaeogeography, Palaeoclimatol- identifiedV. japonica and V. planicostata with A. insignis. ogy, Palaeoecology, vol. 202, p. 245–252. In the late Pliocene, V. japonica was alive on the Japan Amano, K., 2007: The Omma-Manganji fauna and its temporal change. Sea side of Honshu. In the early to middle Pleistocene, V. Fossils (Kaseki), no. 82, p. 6–12. (in Japanese with English abstract) planicostata existed on the Pacific side of central Honshu. Amano, K., Hamuro, M., Hamuro, T., Sato, T. and Ogihara, R., 2012: Both species were associated with some warm-water mol- Influence of the latest Pliocene cooling to the benthic fauna from luscs (Baba, 1990; Amano et al., 2000a, 2011; Nemoto the central part of the Japan Sea borderland: Molluscan fauna from and O’Hara, 2005). Each species of this genus possibly the Zukawa Formation in Toyama Prefecture. Journal of the Geo- evolved by adapting to a higher temperature, but did not logical Society of Japan, vol. 118, p. 810–822. (in Japanese with English abstract) develop a large population or wide distribution. On the Amano, K., Hamuro, M. and Sato, T., 2008: Influx of warm-water cur- Japan Sea side of Honshu, V. japonica suffered extinc- rent to Japan Sea during the Pliocene-based on analyses of mol- tion at least by the cooling event at Datum A (2.75 Ma; luscan fauna from the Mita Formation in Yatsuo-machi of Toyama Sato and Kameo, 1996). Up to this time, three genera of City. Journal of the Geological Society of Japan, vol. 114, p. 516– the Omma-Manganji fauna became extinct; Yabepecten 531. (in Japanese with English abstract) Amano, K., Nagata, K., Sato, T., Yanagisawa, Y. and Kurita, Y., 2009: Masuda, 1963, Profulvia Kafanov, 1976 and Pseudamian- Influence of a warm-water current on the northern Fossa Magna tis Kuroda, 1933. All these genera were monotypic during region during the Pliocene, based on analyses of molluscan fauna the Pliocene to early Pleistocene and originated during from the Shitoka Formation and the lowermost part of the Uonuma the Oligocene and Miocene (Iwasaki, 1963; Kafanov, Group along the Kamakurazawa River in Minami-Uonuma City, 1980; Matsubara, 2003). Vermeijia is the fourth record Niigata Prefecture. Journal of the Geological Society of Japan, vol. 115, p. 597–609. (in Japanese with English abstract) of an extinct genus among the Omma-Manganji fauna. Amano, K., Sato, T. and Koike, T., 2000a: Paleoceanographic con- Some characteristic species of the Omma-Manganji ditions during the middle Pliocene in the central part of Japan fauna have been recorded from the Pacific side of cen- Sea Borderland. Molluscan fauna from the Kuwae Formation tral Honshu where Vermeijia planicostata occurred with in Shibata City, Niigata Prefecture, central Japan. 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