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Iba Y.,Ruhr University Bochum | Mutterlose J.,Ruhr University Bochum | Tanabe K.,University of Tokyo | Sano S.-I.,Fukui Prefectural Dinosaur Museum | And 2 more authors.
Geology | Year: 2011

Belemnites, a very successful group of Mesozoic cephalopods, flourished in Cretaceous oceans until the Cretaceous-Paleogene event, when they became globally extinct. Following this event the modern types of cephalopods (squids, cuttlefish, octopus) radiated in the Cenozoic in all oceans. In the North Pacific, however, a turnover from belemnites to the modern types of cephalopods about 35 m.y. before the Cretaceous-Paleogene event documents a more complex evolutionary history of cephalopods than previously thought. Here we show that the modern types of cephalopods originated and prospered throughout the Late Cretaceous in the North Pacific. The mid-Cretaceous cephalopod turnover was caused by cooling and the closure of the Bering Strait, which led to a subsequent faunal isolation of this area. In the Late Cretaceous the former niches of the fast-swimming belemnites were taken over by the modern types of cephalopods, which evolved endemically. The Cretaceous-Paleogene event only allowed the modern types of cephalopods to spread globally and to take over the niches previously held by belemnites. © 2011 Geological Society of America.


Tanabe K.,University of Tokyo | Misaki A.,Kitakyushu Museum of Natural History and Human History | Landman N.H.,American Museum of Natural History | Kato T.,Ibaraki Nature Museum
Lethaia | Year: 2013

The jaw apparatuses of two species of Late Cretaceous Phylloceratina (Ammonoidea), Hypophylloceras subramosum and Phyllopachyceras ezoensis, are described on the basis of well-preserved in situ material from Hokkaido, Japan. Gross morphological and X-ray CT observations reveal that the upper and lower jaws of the two species are essentially similar in their overall structure. Their upper jaws consist of a shorter outer lamella and a pair of larger, wing-like inner lamellae that become narrower and join together in the anterior portion, as in those of other ammonoids. The upper jaws of the two phylloceratid species are, however, distinguishable from those of other known ammonoids by the presence of a thick, arrowhead-shaped calcified rostral tip. The lower jaws of the two species consist of a short, reduced inner lamella and a large, gently convex outer lamella covered with a thin calcareous layer, the features of which are common with the rhynchaptychus-type lower jaws of the Cretaceous Lytoceratina. In the presence of a sharply pointed, thick calcareous tip on upper and lower jaws, the jaw apparatuses of the Phylloceratina resemble those of modern and fossil nautilids, suggesting that they were developed to serve a scavenging predatory feeding habit in deeper marine environments. This and other studies demonstrate that at least some Mesozoic rhyncholites and conchorhynchs are attributable to the Phylloceratina and Lytoceratina. © 2013 The Lethaia Foundation.


Misaki A.,Kitakyushu Museum of Natural History and Human History | Maeda H.,Kyoto University
Island Arc | Year: 2010

The litho- and biostratigraphy of the mid- to upper-Cretaceous System around the Yagumaike Pond in the Aridagawa area, Wakayama, Southwest Japan, were investigated. Many Middle to Late Albian megafossils were found in the strata of a block bounded by faults. It was also revealed that the Upper Cretaceous System of other blocks ranges from the Middle Turonian to Santonian. The Albian megafossil assemblage contains few benthic organisms, in contrast with the abundance of nektons found (e.g. cephalopods). Sedimentological observations of the mudstone profiles also indicate that scarcely or weakly bioturbated, well-laminated mudstone is dominant among the Albian deposits. These results suggest deposition of the Albian mudstone under a dysaerobic to anoxic environment. It is comparable to the extended oceanic anoxia (OAEs) in mid-Cretaceous time. Albian deposits with similar characteristics are also known to exist in Shikoku, Southwest Japan. A wide sedimentary basin that was directly affected by global environmental events, such as OAEs, seemed to be formed on the Chichibu Belt in the Albian. The Upper Cretaceous strata in the study area are extremely thin, similar to the coeval deposits on the Chichibu Belt in Shikoku. It is suggested that the sedimentation rate in the sedimentary basin on the Chichibu Belt was extremely low during early Late Cretaceous time. © 2010 Blackwell Publishing Asia Pty Ltd.


Misaki A.,Kitakyushu Museum of Natural History and Human History | Maeda H.,Kyushu University | Kumagae T.,Japan Petroleum Exploration Co. | Ichida M.,Kyoto University
Palaeontology | Year: 2014

The heteromorph ammonite Pravitoceras sigmoidale from the Upper Cretaceous Seidan Formation (Izumi Group) in south-west Japan is frequently encrusted by sessile anomiid bivalves. Fossils of P. sigmoidale with anomiids are often concentrated at the top of or just above turbidite sandstones. Projecting retroversal hooks and apertures of P. sigmoidale are usually intact, and some individuals are associated with jaw apparatuses near apertures. Anomiids are found on both sides and ventral peripheries of P. sigmoidale conchs, attached predominantly to body chambers. These modes of occurrence suggest that the encrustation by anomiids occurred not on post-mortem floating or sunken carcasses but on live conchs and that these organisms were rapidly buried by turbidity current deposits shortly after death. Attachment to both flanks and ventral peripheries of the retroversal hooks may indicate that at least adult individuals of P. sigmoidale did not lie on the sea floor and did not drag their body chambers. It is suggested that fully mature individuals of this ammonite species lived for a long period of time after having formed the retroversal hook because a few generations of anomiids have colonized a single body chamber. Such colonization by anomiids is also observed on Didymoceras awajiense, which is considered to be the closely related ancestral species of P. sigmoidale. This anomiid-heteromorph ammonite commensal relationship might continue to persist in descendants during the course of evolution of these heteromorph ammonites. © The Palaeontological Association.


Misaki A.,Kitakyushu Museum of Natural History and Human History | Ohara M.,Wakayama Prefectural Museum of Natural History
Paleontological Research | Year: 2011

Late Cretaceous heteromorph ammonoids, Ainoceras kamuy and Ainoceras paucicostatum, were discovered for the first time from the Futakawa Formation in the Aridagawa area, Wakayama, southwestern Japan. Other molluscan fossils such as Eupachydiscus sp., Gaudryceras aff. striatum, "Gigantocapulus" transformis, Sphenoceramus nagaoi, Sphenoceramus orientalis and Inoceramus balticus also cooccur with Ainoceras, and together they indicate the lower Campanian Stage. Recently, the middle TuronianSantonian and upper lower CampanianMaastrichtian litho- and biostratigraphy in the Aridagawa area was established. Therefore, the lower Campanian strata in the study area fill the gap between them and supplement the Upper Cretaceous stratigraphy in the Aridagawa area. The results of this study advance the biostratigraphy and correlation of the marine Cretaceous strata in the northwestern Pacific region. © 2011 by the Palaeontological Society of Japan.


Shigeno M.,Kumamoto University | Mori Y.,Kitakyushu Museum of Natural History and Human History | Shimada K.,Kyushu University | Nishiyama T.,Kumamoto University
European Journal of Mineralogy | Year: 2012

Petrography, isocon analysis and singular value decomposition analysis of jadeitites and metasomatic rocks surrounding them from the Nishisonogi metamorphic rocks revealed that the metasomatic rocks developed outside the stability field of jadeite + quartz after jadeitites had been included by a serpentinite mélange in a subduction channel possibly during exhumation. The jadeitites occur at two localities, Tone and Mie in Nagasaki City, from a serpentinite mélange in the Nishisonogi metamorphic rocks. The jadeitite mineral assemblage is jadeite/omphacite + paragonite + phlogopite + albite + clinozoisite/epidote ± muscovite ± analcime. Jadeite core with fine-grained quartz inclusions and the inclusion-free rim is partially replaced by albite. These jadeitites are surrounded by metasomatic zones of albitites and/or a muscovite rock. The mineral assemblage of the albitites is albite + clinozoisite/epidote ± muscovite ± omphacite ± phlogopite ± amphibole ± chlorite, and that of the muscovite rock is muscovite + clinozoisite + chlorite. Because these zones have no high-pressure minerals, they represent products in a P-T regime outside the stability field of jadeite + quartz. Isocon analyses between the jadeitites and the metasomatic zones reveal that K2O, H2O, Sr and Ba were added to jadeitite and SiO2, Na2O and Fe2O3 were removed. REE-rich veinlets emanate from clinozoisite grains, suggesting REE mobility during the fluid-jadeitite interactions. The metasomatic zones developed by interaction between jadeitites and serpentinite via K-, Sr- and Ba-rich fluid, during exhumation from the stability field of jadeite + quartz through that of albite to that of analcime. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung.


Mori Y.,Kitakyushu Museum of Natural History and Human History | Orihashi Y.,University of Tokyo | Miyamoto T.,Kyushu University | Shimada K.,Kyushu University | And 2 more authors.
Journal of Metamorphic Geology | Year: 2011

On the basis of internal structures, laser ablation U-Pb ages and trace element compositions, the origin of zircon in jadeitite in the Nishisonogi metamorphic rocks was examined. The zircon comprises euhedral zoned cores overgrown by euhedral rims. The cores contain inclusions of muscovite, quartz, albite and possibly K-feldspar, yield 238U-206Pb ages of 126±6Ma (±2SD, n=45, MSWD=1.0), and have Th/U ratios of 0.48-1.64. The rims contain inclusions of jadeite, yield 238U-206Pb ages of 84±6Ma (±2SD, n=14, MSWD=1.1), and have Th/U ratios of <0.06. The cores are richer in Y, Th, Ti and rare earth elements (REEs), but the rims are richer in Hf and U. Chondrite-normalized REE patterns of the cores indicate higher SmN/LaN ratios, lower YbN/GdN ratios and larger positive Ce anomalies compared with those of the rims. Thus, the cores and rims have different 238U-206Pb ages and trace element compositions, suggesting two stages of zircon growth. Although the 238U-206Pb ages of the rims are consistent with the reported 40Ar/39Ar spot-fusion ages of matrix muscovite in the jadeitite, the 238U-206Pb ages of the cores are older. The mineral inclusions and high Th/U ratios in the cores are best explained by crystallization from felsic magma. Therefore, the cores are considered relicts from igneous precursor rocks. The rims surrounding the inherited cores possibly precipitated from aqueous fluids during jadeitite formation. The elevated U concentrations in the rims suggest that infiltration of external fluids was responsible for the precipitation. This study provides an example of jadeitite formation by metasomatic replacement of a protolith. © 2011 Blackwell Publishing Ltd.


Shimomura M.,Kitakyushu Museum of Natural History and Human History
ZooKeys | Year: 2016

A new mysid, Mysidella hoshinoi sp. n. is described from Izu-Oshima Island, Sagami Sea, central Japan. This species differs from its congeners in having a posterodorsal finger-like papilla on the eyestalk, five peculiar spines terminating in plumed seta on outer margin of carpopropodus of endopod of first thoracopod, and uropodal endopod bearing 27 spines on inner margin. © Michitaka Shimomura.


Komoto N.,Japan National Institute of Agrobiological Science | Yukuhiro K.,Japan National Institute of Agrobiological Science | Ueda K.,Kitakyushu Museum of Natural History and Human History | Tomita S.,Japan National Institute of Agrobiological Science
Molecular Phylogenetics and Evolution | Year: 2011

Phasmids are remarkable mimics of twigs, sticks, and leaves. This extreme adaptation for crypsis can easily lead to the convergent evolution of morphology, making it difficult to establish a taxonomic system of phasmids. Accordingly, there are multiple phylogenetic hypotheses that conflict with each other. Phylogenetic arrangements suggested by molecular data disagree with the morphology-based taxonomy in some instances. We collected 13 phasmatodean species, sequenced their mitochondrial genomes, and recovered their molecular phylogeny. Our analyses did not support the monophyly of Areolatae or Anareolatae, two major infraorders of Phasmatodea. The position of Neohirasea was also quite different from the conventional taxonomic systems, thus challenging the previously assumed monophyly of the subfamily Lonchodinae. The enigmatic taxon, Timema, was shown to be distantly related to other phasmatodeans. © 2010 Elsevier Inc.


Yabumoto Y.,Kitakyushu Museum of Natural History and Human History
Paleontological Research | Year: 2014

A new species of the genus Sinamia of the family Sinamiidae of the order Amiiformes, S. kukurihime is described on the basis of a hyomandibula and many isolated bones and scales found from the Lower Cretaceous freshwater deposits of the Kuwajima Formation, Itoshiro Subgroup, Tetori Group in Kuwajima, Hakusan City, Ishikawa Prefecture, Japan. The new species is distinguished from other congeners by the forms of the hyomandibular, frontal, dermopterotic, maxilla, gular plate, preopercle, supracleithrum and scales. Among the genus Sinamia, S. kukurihime sp. nov. is considered to be closest to S. liaoningensis. This is the first record of the genus Sinamia from Japan. The presence of a new species of the genus from Japan demonstrates the wide distribution and diversity of the genus during the Cretaceous in East Asia. © 2014 by the Palaeontological Society of Japan.

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