Fortipecten takahashii (Yokoyama, 1930)
YOKOYAMA, M. 1930. Tertiary Mollusca from south Karafto. Journal of the Faculty of Science, Imperial University of Tokyo, Section II, Vol. 2(10): 407-418 [p. 416, pl. 78, figs. 1, 2; pl. 79, figs. 1, 2]
1930 Pecten takahashii Yokoyama, 1930
1930 Pecten agnatus Yokoyama, 1930
1931 Pecten piltunensis Khomenko, 1931
1930 Pecten agnatus Yokoyama, 1930
1931 Pecten piltunensis Khomenko, 1931
M. Yokoyama, 1930, plates 78, 79.
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«Shell large, thick, round, somewhat higher than long, very inequivalve, equilateral save for ears. Right valve strongly convex, convexity being equal to one-third to two-fifths of height, radiately ribbed, with ribs about fourteen in number, equal, straight, rounded, narrower than interstices, occasionally crossed by interruptions in growth which make the cross-points more 01' less nodose; ears nnequal, triangular, anterior larger than posterior, with a shallow byssal notch below. Left valve almost or quite flat, radiately ribbed, with ribs ten to twelve in number, somewhat unequal, narrow, rounded at top, much narrower than interstices, occasionally made nodose by interruptions in growth; sometimes ribs as well as interstices finely radiately striate; ears unequal, triangular, anterior a little larger than posterior, with coarse lines of growth. Inner margin of both valves coarsely crenate.
A few examples. One measures 133 millim. in height, 126 millim. in Iength and about 40 millim. in thickness. Another measures 130 millim. in height, 118 millim. in length, and 56 millim. in thickness. This shell in its general appearance resembles Pecten poculurn Yok. (Tert. Moll. Oilf. Embets a. Etaibets, pI. XXXII, figs. 1-3), but has tbe ribs less and coarser. Fossil occurrence — Isos, Higashi-Sakutan, Motodomari-gun.» MATAJIRO YOKOYAMA, 1930
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«The migration route of Fortipecten takahashii was thought to have been from northern Honshu to Hokkaido, Sakhalin, and Kamchatka on the basis of the times of its occurrence (Masuda, 1986; Sagayama, 1993), although Uozumi et al. (1986) inferred that this species originated in central Hokkaido and migrated southward to northern Honshu and northward to Sakhalin and Kamchatka. However, on the basis of updated age data (Fig. 3), the history of the geographic distribution of Fortipecten appears more complicated. Fortipecten takahashii first appeared in central Hokkaido in the very late Miocene (about 7 Ma; the Miocene-Pliocene boundary is at 5.32 Ma). In the transition from Miocene to Pliocene (6-5 Ma), F. takahashii extended its range southward to Aomori and Miyagi, northern Honshu, and Fortipecten kenyoshiensis evolved from F. takahashii at this time. Both species of Fortipecten moved farther north, to Sakhalin and Kamchatka, in the early Pliocene (5-4 Ma), whereas in the middle Pliocene (4 Ma) the whole distribution of Fortipecten shifted southward to range from northern Sakhalin to Fukushima, northern Honshu. In the middle Pliocene (4-3 Ma), Fortipecten disappeared from northern Honshu. In the latest Pliocene to early Pleistocene (3-1 Ma), although F. kenyoshiensis expanded episodically to Akita on the side of the Sea of Japan, the geographic range of F. takahashii contracted, so that this species lived only in northern Hokkaido and in Sakhalin.»
NAKASHIMA, R. 2002. Geographic distribution of the late Cenozoic bivalve Fortipecten in the northwestern Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology, 186 (3): 261-274, figs. 1-4. [p. 269]
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Fortipecten takahashii (Yokoyama); R. Nakashima, 2002, Geographic distribution of the late Cenozoic bivalve Fortipecten in the northwestern Pacific, figures 2.1a, 2.1b, 2.2.
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«Since Kuroda (1932) assigned P. takahashii to Patinopecten, many authors have considered that this pectinid should be taxonomically placed in or near that genus. In fact, the young shell of Pecten takahashii, as shown later in detail, is weakly convex, thin-shelled, and considerably similar to Patinopecten (Mizuhopecten) yessoensis (Jay, 1857), a commercial scallop in the north-western Pacific. Since Yabe and Hatai (1940) proposed the subgenus Fortipecten for Pecten takahashii, most palaeontologists have regarded it as a valid genus-group name, but some different taxonomic evaluations have been made about the peculiar morphology of this species. For example, Akiyama (1962) regarded the heavy and strongly inflated shell as due to adaptation to some lagoonal environment and denied its subgeneric distinction from Patinopecten. In contrast, Masuda (1962a) treated Fortipecten as a distinct genus, and furthermore a new subfamily Fortipectininae was proposed (Masuda 1963).
In addition to Pecten takahashii, the following species seem to belong to Fortipecten, though their diagnostic characters are not necessarily clear: Pecten (Plagioctenium) hallae Dall, 1921, from the Pliocene of east Alaska. [? = P. (Patinopecten) rhytidus Dall, 1921]. P. mironovi Khomenko, 1934, from the Pliocene of Sakhalin. P. (P.?) sachalinensis Ilyina, 1957, from the Pliocene of Sakhalin. P. (Fortipecten) kenyoshiensis Chinzei, 1960, from the Pliocene of north Honshu. P. (F.) makarovi Kryshtofovich, 1964, from the Pliocene of Sakhalin. Fortipecten mollerensis MacNeil, 1967, from the Pliocene or Upper Miocene of south Alaska. F. kuroishiensis Kotaka and Noda, 1967, from the Upper Miocene of north Honshu. Because the intrapopulational and geographic variation of each species may be wide, its taxonomic discrimination and phylogenetic relation to other species should be studied at the population level. In this paper we do not discuss this problem, because the examined material is still restricted to several samples from north Japan and south Sakhalin.» HAYAMI, I. & I. HOSODA. 1988. Fortipecten Takahashii, a reclining pectinid from the Pliocene of North Japan. Palaeontology, 31 (2): 419-444. [p. 420, 421]
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Fortipecten takahashii (Yokoyama, 1930); I. Hayami & I. Hosoda, 1988, Fortipecten Takahashii, a reclining pectinid from the Pliocene of North Japan, plate 39.
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«Since YOKOYAMA (1930) described Pecten tahahashii from the Pliocene Maruyama Formation in South Sakhalin, the species was frequently recorded from the Pliocene formations in Japanese Islands and Sakhalin. In 1940 YABE & HATAI established the genus Fortipecten based upon P. takahashii Yokoyama.
The genus Fortipecten has hitherto been considered to be an important Pliocene pectinid of Northern Japan, until KOTAKA & NODA (1967) described F. kuroishiensis from the middle Miocene Ogawara Formation, Aomori Prefecture, Northern Honshu, Japan. Among three species of Fortipecten, F. takahashii, F. kenyoshiensis and F. kuroishiensis, known from the Japanese Islands, F. tahahashii is the most important species, particularly from the viewpoint of its restricted geological range and very wide geographical disribution from middle Northern Honshu northward to Hokkaido and Sakhalin and Kamchatka (MASUDA, 1962b). On the other hand, several species such as Fortipecten takahashii, F. pilutunensis [sic], F. sachalinensis, and F. mironovi, have been described from North Sakhalin and Kamchatka (KHOMENKO, 1931; SLODKEWITSCH, 1938; ILYNA, 1963; KRISHTOFOVICH, 1964). And F. hallae (Dall) (MACNEIL, 1943) and F. mollerensis MacNeil (1967) have been described from Alaska. Therefore, the occurrence of Fortipecten in the Circum North Pacific is a result of migration from the Japanese Islands. However, those mentioned species are in need of further study to clarify their taxonomic relations. For example, according to the present writer's study based upon the holotype and topotype of F. mollerensis MacNeil, it is evident that MacNeil's mollerensis is different from Fortipecten and should be referred ro Mizuhopecten.» MASUDA, K. 1978. Neogene Pectinidae of the Nothern pacific. The Veliger, 21 (2): 197-202. [p. 199]
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«The species is very variable with respect to the size of the valves, their thickess, number of ribs and even their form, which in general becomes rounded at top. Masuda (1962a), comparing specimens from south of Sakhalin and the neighborhood of Sindia, observed that most of the convexed right valve and most of the heavy shells belonged to the southern Sakhalin forms, while the Sindian ones were more thin and less convex. In the south of Sakhalin in Makarovskii region at the upper part of Marvam suite, a series of beds were observed, which were crowded with shells of F. takahashii, outcropping some 4 Km north of Makarov town on the shore of the Okhotsk Sea. The lower 2 horizons contain considerable amount of specimens of this species, usually slightly thick and with broken valves. Here the most flat right valves of F. takahashii are observed. At the top-lying horizons, there are absolutely adult, as well as young valves of this species, usually in their life-time state. The young specimens have fairly thin shells, more rounded ribs, left valve near to the beak is slightly convex, later on becomes nearly flat or even concave. But after that the margin of the disk and the pallial margin again acquire convexity. At the apex, in all well-preserved valves, a fine network sculpture is observed, which maintains the sculpture of the recent Mizuhonecten yessoensis (Jay). Adult shells are very large and thick. The left valve is thickened with the pallial margin. In some large forms on the left valve, even in older forms, a network sculpture is nearly preserved on all the disk of the shell, and it is distinct especially at the beak and the margin of the disk through the articulation wth the auricles. The network is much wider and coarser than in the young shells. In case of bad preservation and slightly-eroded network, sculpture disappears. In general, the broad ribs always become narrower than the intercostal intervals and the general form of the shell in the adult stage becomes more or less constant. But in the young specimens, the shells are usually of rounded form and not sharply inflated.»
SINELNIKOVA, V. N. 1975. Mio-Pliocene Pectinidae of Kamchatka [Pektinidy mio-pliotsena Kamchatki]. Transactions of the Geological Institute, Academy of Sciences of the USSR, 229: 1-140, 25 pls. (in Russian with English title and contents (in Russian with English title and contents; Translated for the U. S. Department of the Interior, Geological Survey, and the National Science Foundation, Washington, D. C., by the Al-Ahram Center for Scientific Translations, 1977). [p. 36, 37]
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Fortipecten takahashii (Yokoyama); V. N. Sinelnikova, 1975, Mio-Pliocene Pectinidae of Kamchatka, plate 1.
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«Remarks. This species is characterized by the much convex, thick right valve provided with 11-15 round-topped radials narrower than interspaces, and the thick, slightly convex left valve with 11-13 narrow, round-topped radials of which every second or third radials are more conspicuous than the others. Hinge straight and with rather incospicuous cardinal crura only near the pit and the large resilial pit provided with distinct, sharp ridges on both margins in the right valve and with inconspicuous furrow corresponding to the cardinal crura of the right valve in which numerous taxodont teeth-like ridges are developed in some specimens.
The present species is associated with the Tatsunokuchi-Takikawa fauna characterized by the thick-shelled species which were adapted to a lagoonal environment. DALL said in his paper (1898), "The influence of the environment is very marked among the Pectens.......The specimens which live in deep water and swim actively are usually thinner-shelled and smoother, while those which inhabit the lagoons are heavier, have more conspicuous concentric sculpture, and more solid shells. These differences are very marked in our common east coast P. irradians, of which P. dislocatus Say is the southern lagoon form; and parallel differences appear in the similarly related P. ventricosus and its variety aequisulcatus, on the Pacific coast, and in the fossil P. eboreus and comparilis of the Carolina Tertiaries". Being much allied to P. matumoriensis in its shell sculpture P. takahashii may be a descendent species of matumoriensis adapted to a lagoonal environment which caused much convex and thick shells. In the Tatsunokuchi-Takikawa fauna P. kenyoshiensis was reported by CHINZEI (1960) which has much convex and thick shells like takahashii, but kenyoshiensis is derived not from maturnoriensis but from yessoensis. YABE and HATAI (1940) established the subgenus Fortipecten on the basis of this species which has much convex and thick valves. From the above mentioned facts it is supposed that Fortipecten should not be admitted and this species should be inclued in the subgenus Patinopecten. Comparisons. The present species is much allied to P. matumoriensis which is supposed to be an ancestral species, but can be distinguished from the latter by the more convex and thick valves with large auricles and with every second or third radials more conspicuous in the left valve. P. murayamai and P. kimurai are allied species, but can be distinguished from takahashii by the more convex and thick valve with larger auricles and more numerous radials. Type locality. Isos. Higashi-Sakutan, Southerm Sakhalin. Naikawa bed. Distribution. Supranutovo series and its equivalents in Sakhalin, Takikawa and Hombetsu formations in Hokkaido, Togawa formation in Aomori Prefecture and Tatsunokuchi formation in Miyagi Prefecture.» AKIYAMA, M. 1962. Studies on the phylogeny of
Patinopecten in Japan. Science Reports of the Tokyo Kyoiku Daigaku [Section C -
Geology, Mineralogy and Geography], 8 (74): 63-122, pls. 1-8, text-figs. 1-3. [p. 91, 92]
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«Remarks:— Fortipecten hallae (Dall) (MacNeil, Mertie and Pilsbry, 1943, p. 86, pI. 12, figs. 1, 2, pI. 13, fig. 1) from the Pliocene of Alaska is closely related to the present species, but it differs by its less inflated right valve, the radial ribs which are broader than their interspaces and rather smaller auricles in the right valve, and by the left valve having the fine, somewhat pointed radial ribs. Although Patinopecten yessoensis is easily distinguishable from the adult specimens of the present one, sometimes it is difficult to distinguish them in the very young stage.
From the type locality of the present species, Yokoyama also described Pecten agnatus, n. sp., but from its illustration and description it is a synonym of takahashii, because his agnatus seems to be the young shell of takahashii. Khomenko (1931) described Pecten pilutunensis [sic] from the Supranutovo series in North Saghalien. Yabe and Hatai (1940) identified Khomenko's fig. 1 of plate 1 and figs. 1 and 2 of plate 2 with takahashii and did not identify the other figures with takahashii. However, judging from the figures of pilutunensis [sic] given by Khomenko, there seems to be no doubt as to all his figures belonging to takahashii.» MASUDA,
K. 1962. Tertiary Pectinidae of Japan. Science Reports of the Tohoku University [2nd. Series - Geology], 33 (2): 117-238, pls. 18-27. [p. 222, 223]
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Fortipecten takahashii (Yokoyama); K. Masuda, 1962, Tertiary Pectinidae of Japan, plate 26, figures 13-15.
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