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Hokkaido, Japan

Shigeta Y.,National Museum of Nature and Science | Nishimura T.,Hobetsu Museum
Paleontological Research | Year: 2013

Gaudryceras hobetsense sp. nov. is described from the Nostoceras hetonaiense Zone (= lowest Maastrichtian) of the Hobetsu area, south-central Hokkaido, Northern Japan. Its shell is characterized by fine lirae on early whorls, distant rounded or flat-topped, narrow band-like ribs on middle and later whorls, and frequent collar-like ribs on later whorls. The occurrence of this new species strongly suggests the presence of lowest Maastrichtian strata in southern Alaska, and sheds light on the age delineation of the chronologically poorly defined beds in northern and eastern Hokkaido. © by the Palaeontological Society of Japan. Source

Fuchs D.,Free University of Berlin | Iba Y.,Hokkaido University | Ifrim C.,University of Heidelberg | Nishimura T.,Hobetsu Museum | And 4 more authors.
Palaeontology | Year: 2013

The phylogenetic origin and the timing of origination of the Decabrachia are controversial. This is due to a poor understanding of character complexes relating to the shell, which causes difficulties in establishing homologies among different taxa. One central problem concerns a clear differentiation between belemnoids and early spirulids. A comparative analysis of shell structures of well-preserved specimens including types and new material of Cretaceous spirulids Groenlandibelus, Naefia and Cyrtobelus, as well as selected taxa of aulacocerid, belemnitid and diplobelid belemnoids, revealed a set of 14 characters. Seven characters (apical angle, chamber length, dorsal and ventral sutures, orientation of septa, direction of the dorsal part of the septal neck, primordial rostrum) are not or less diagnostic, whereas the seven remaining characters can be reliably used to distinguish between the Decabrachia on the one hand and Belemnitida and Aulacocerida on the other hand. These diagnostic characters are as follows: (1) presence/absence of a mural flap; (2) position of the siphuncle; (3) shape of the dorsal soft tissue attachment scar; (4) presence/absence of tabular nacre in the conotheca; (5) presence/absence of a rostrum proper; (6) presence/absence of a narrow rod-like proostracum; and (7) presence/absence of a caecum. Diplobelida and 'Naefia' matsumotoi, however, exhibit a mosaic of decabrachian and belemnoid characters. Owing to striking differences between N. neogaiea, the type species of Naefia, and 'N.' matsumotoi, the new genus Longibelus has been erected. Besides a redescription of Longibelus ('Naefia') matsumotoi, we describe the first Maastrichtian occurrences of this species from Hokkaido (northern Japan) and Alaska. Among the type material of N. neogaiea from the Maastrichtian of Chile, we found one specimen that unambiguously belongs to Longibelus gen. nov. Similarly, two specimens from the Maastrichtian of Mexico previously determined as N. neogaiea also belong to the new genus. Also, we can reinterpret material from the Cenomanian of India as Longibelus gen. nov. New material from the Albian of India likewise assignable to Longibelus is described for the first time. Finally, we introduce the first records of coleoids from Zululand (South Africa). These specimens belong to Longibelus as do specimens from the Aptian of Caucasus (previously described as 'Naefia' kabanovi). A phylogenetic approach suggests that Longibelus gen. nov. is derived from diplobelid-like belemnoids and gave rise for the Decabrachia or at least groenlandibelid spirulids. This strongly supports earlier ideas on a close relationship between Cretaceous Decabrachia and belemnites and simultaneously challenges opinions that Decabrachia originated in the Carboniferous. © The Palaeontological Association. Source

Shigeta Y.,National Museum of Nature and Science | Nishimura T.,Hobetsu Museum
Paleontological Research | Year: 2013

A new Cretaceous heteromorph ammonoid, Phylloptychoceras horitai sp. nov., is described from the lowest Maastrichtian of Hokkaido, Japan. Its shell is ornamented with very weak, broadly rounded ribs and its suture line is characterized by a deeply incised, trifid dorsal lobe and three bifid lateral saddles with minor indentations. This occurrence suggests that Phylloptychoceras evolved in the North Pacific during late Campanian or early Maastrichtian time and then achieved worldwide distribution during late Maastrichtian time. © by the Palaeontological Society of Japan. Source

Tanaka G.,Gunma Museum of Natural History | Ono T.,1552 141 Honden | Nishimura T.,Hobetsu Museum | Maeda H.,Kyoto University
Paleontological Research | Year: 2013

Samples of Middle Permian organic-rich black unconsolidated mud were collected from a fissure of black limestone in Kinshozan Mountain, Akasaka City, Gifu Prefecture, central Japan. Nine new species, one new genus and one new family are described herein: Ikeyaparchitidae Tanaka fam. nov., Gifuaparchites Tanaka and Maeda gen. nov., Aurikirkbya kinshozanensis Tanaka sp. nov., Gifuaparchites takagii Tanaka and Maeda sp. nov., Cavellina hashintotoi Tanaka and Maeda sp. nov., Bairdia nishiwakii Tanaka and Nishimura sp. nov., Bairdia akasakaensis Tanaka sp. nov., Bairdia oogakiensis Tanaka sp. nov., Bairdiacypris? hayasakai Tanaka sp. nov., Acratia? okumurai Tanaka sp. nov., and Acratia? hamadai Tanaka, Ono and Maeda sp. nov. This is the first report from Japan of a typical Panthalassa ostracod assemblage during the Middle Permian, and of which is characterized by typically endemic species. © by the Palaeontological Society of Japan. Source

Nishimura T.,Hobetsu Museum | Maeda H.,Kyoto University | Tanaka G.,Gunma Museum of Natural History | Ohno T.,Kyoto University
Paleontological Research | Year: 2010

Intra- and interspecific variation and ontogenetic changes in various shell characters of the Late Cretaceous desmoceratine ammonoid "Damesites" are described, and their taxonomic implications are discussed based on specimens from the Cretaceous Yezo Group in Hokkaido and Sakhalin. Our study reveals that many "diagnostic" features (e. g., appearance of longitudinal striations, height of ribbing, regularity of ribbing as well as constriction curvature) and early internal shell structures, are in fact inappropriate as diagnostic features of "Damesites" morphotypes. In contrast, ontogenetic changes in shell ornament, curvature of growth lines and whorl expansion ratio are herein demonstrated to be key characters for species recognition and reconstructing the phylogenetic relationships of the taxa of the subfamily Desmoceratinae. Based on these results, previously described "Damesites" species from the uppermost Turonian-lower Campanian interval should be reclassified into three groups. "Damesites damesi," "D. damesi intermedius," "D. semicostatus," and "D. laticarinatus" are assigned to the first group. "D. ainuanus" and "Damesites sp." are assigned to the second group. "D. sugata" from the Yezo Group represents the third group. Furthermore, analysis of ontogenetic changes in shell ornament, curvature of growth lines, and whorl expansion ratio suggests that the second and third groups together belong to a different evolutionary lineage from the first group. © by the Palaeontological Society of Japan. Source

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