Vol.22 No.4

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Two mandibles of fossil mysticetes from the early Pliocene, upper part of the Horokaoshirarika Formation at Numata Town, Hokkaido, Japan, belong to the archaic, extinct cetotheriid baleen whale, Herpetocetinae, gen. et sp. indet. by having an elongated angular process projecting posteriorly beyond the mandibular condyle. The new materials of the Herpetocetinae represent the northernmost occurrence in the North Pacific.

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The Upper Cretaceous Nakaminato Group, which contains the Chikko, Hiraiso, and Isoai formations in ascending order, crops out along the Pacific coast of Ibaraki Prefecture, central Japan. This group is composed mainly of sandstone, siltstone, and sandstone-siltstone alternations, with intercalated conglomerate layers at several levels. The siltstone of the Hiraiso and Isoai formations has yielded ammonites and inoceramid bivalves indicating a middle Campanian to Maastrichtian age. Some conglomerate layers in the Isoai Formation reach 1 m in thickness and mostly consist of pebbles and cobbles of rhyolite, dacite, chert, siliceous siltstone, siltstone, sandstone, and hornfels. We obtained late Paleozoic to Late Jurassic radiolarians from pebbles of argillaceous rock and chert from four levels of the conglomerate layers within the Isoai Formation. We describe the radiolarians systematically herein. The probable provenance of the radiolarian-bearing pebbles is interpreted as the Ashio and Yamizo terranes, which consist of Late Jurassic to Early Cretaceous accretionary complexes. We propose that there were two denudation stages of the accretionary complexes in the Kanto District, stages α (Barremian–) and β (Campanian–).

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We studied the deep-sea benthic foraminiferal fauna from core NGC108 (36°36.85′N, 158°20.90′E; 645 cm long, recovered from 3,390 m water depth) collected from the Shatsky Rise in the central northwestern Pacific Ocean, to determine the relationship between benthic foraminifera and paleoproductivity in the transitional zone between the subtropical Kuroshio Extension and the subarctic current over the last 187 kyr. Cassidulina reniforme, Eilohedra levicula, and Epistominella exigua were the most abundant species. The relative abundance of C. reniforme was positively correlated with biogenic opal and organic carbon contents, which are proxies for paleoproductivity. The relative abundance of E. exigua was negatively correlated with biogenic opal and organic carbon contents, and the relative abundance of E. levicula had no correlation with biogenic opal and organic carbon contents. We conclude that C. reniforme and E. exigua are indicative of high and low productivity, respectively. The high relative abundances of C. reniforme reflect high paleoproductivity during glacial periods [oxygen isotope stages (OISs) 6, 3, and 2], indicating a southward advance of the Subarctic Front during global cooling. The high relative abundances of E. exigua reflect low paleoproductivity during the interglacial and postglacial periods (OISs 5 and 1). Faunal changes in the deep-sea benthic foraminifera on the Shatsky Rise suggest a direct response to orbital-scale paleoproductivity changes.

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A fish fossil found from the Miocene Bessho Formation near Amikake, Sakaki Town, Hanishina County in Nagano Prefecture, central Japan is described as a new species of the genus Clupea, C. macrocephala of the family Clupeidae of Clupeiformes. This new species differs from other species of the genus in having a large head about 3.4 times in the standard length versus more than 4 times in other species. Clupea macrocephala sp. nov. is closer to Clupea pallasii than Clupea harengus in the number of vertebrae. Presence of the fossil herrings of the genus Clupea in the deposits of Pacific basin implies that the origin of this genus, probably, was in the Pacific Ocean in the Miocene.

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A nearly complete right mandibular tooth plate of Ischyodus bifurcatus Case (Holocephali: Chimaeroidei) is reported from the Point Loma Formation (upper Campanian) of the Upper Cretaceous Rosario Group in southern California, USA. The individual is estimated to have measured nearly 1 m in total body length. Remains of I. bifurcatus have been reported from marine rocks deposited in epicontinental seas and continental shelf paleoenvironments of temperate latitudes in the Northern Hemisphere. Previous records of the species consist of specimens from Santonian to Maastrichtian strata of the US (Delaware, New Jersey, North Carolina, Georgia, Alabama, Arkansas, Montana, and Wyoming), Sweden, and European Russia. The tooth plate described herein is the first verifiable record of I. bifurcatus from California, and more significantly, represents the only known definite Mesozoic record of Ischyodus from the entire North Pacific region.

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Faunal composition and correlation of the late Carboniferous and Permian fusulines contained in exotic limestone blocks of the Sakamototoge area, Gifu Prefecture, Japan were reconsidered. Main alterations of the previous results are summarized as: (1) Moscovian fusulines are confined to the Myachkovian; (2) many species collectively included in Triticites are attributed to Protriticites, Montiparus, Rauserites, Triticites, or Schwagerina; (3) “Triticites” faunas designated as the Carboniferous–Permian are reorganized into three faunas: Protriticites subschwagerinoides (early Kasimovian), Montiparus mesopachus-Protriticites kiyomiensis (middle Kasimovian), and Rauserites arcticus-Carbonoschwagerina nakazawai-Quasifusulina longissimi (late Kasimovian to possibly early Gzhelian); and (4) the species assigned to Pseudoschwagerina is now attributed to late Gzhelian Carbonoschwagerina, implying the probable absence of the Asselian in the area. In addition, the Capitanian Yabeina fauna heterogeneous to the coeval neoschwagerinid faunas in the Permian terranes of Japan is ascertained.