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Tanaka G.,Gunma Museum of Natural History | Taniguchi H.,Oita Industrial Research Institute | Maeda H.,Kyoto University | Nomura S.-I.,Kyoto University
Geology | Year: 2010

Greenish-blue metallic colored fossil elytra of the leaf beetle (Plateumaris sp.) have been discovered in the peat sediment of the middle Pleistocene (ca. 600 ka) Hirabaru Formation, Kyushu, Japan. Scanning and transmission electron microscopy revealed the smooth outer surface of the fossil elytra and five alternating electron-dense and electron-lucent layers in the epicuticle. By applying the matrix method to the epicuticle, three reflective peaks of wavelengths 388 nm, 544 nm, and 656 nm were computed. These peaks correspond to the reflective color observed under white light. Thus, the coloration of the fossils was caused by multilayer reflectors of the epicuticle of the elytra. Pyrolysis-gas chromatography-mass spectrometric analysis revealed that the fossil elytra have preserved some of their original macromolecules (chitin, protein, and amino acids), which are similar to those of a related Holocene species. The high-porosity matrix of the peat contains many fragments of diatoms, indicating the high productivity of the water column but a reducing bottom environment. Slight acidity of the interstitial water also seems to contribute to the preservation of some original macromolecules of fossil insects through geologic time. © 2010 Geological Society of America.


Naruse H.,Kyoto University | Arai K.,Chiba University | Matsumoto D.,Japan Advanced Institute of Science and Technology | Takahashi H.,Chiba University | And 3 more authors.
Sedimentary Geology | Year: 2012

The March 11, 2011 Tohoku-Oki tsunami triggered by an earthquake off the east coast of northeastern Honshu Island (Tohoku region), Japan, deposited large amounts of sediment on land, including the Sendai Plain and Sanriku Coast. This study reports on the characteristics of the tsunami deposits in Rikuzentakata City, southeastern Iwate Prefecture, northeastern Japan. A field survey identified the inundation pattern of the tsunami in this region and the facies model of the tsunami deposits at the bay-head deltas of estuarine systems. The tsunami deposits in Rikuzentakata City generally consist of one to four units that represent a discrete runup or backwash flow. Each unit is characterized by initial inverse grading and successive normal grading that correspond to the accelerating and decelerating stages of the flow, respectively. An internal erosional surface often developed between the inverse-graded and normal-graded units. It corresponds to the maximum shear velocity of the flow and truncates the underlying inverse-graded unit. In the case of the runup unit, silty fine-grained drapes overlay the graded sandy interval. A correlation of the sedimentary structures and grain fabric analysis revealed that the Tohoku-Oki tsunami inundated Rikuzentakata City at least twice and that the flow velocity exceeded 2.4. m/s. Paleontological analysis of the sediment and kriging estimation of the total volume of the tsunami deposit implied that the sediments were sourced not only from eroded beach sands but also from the seafloor of Hirota Bay or more offshore regions. © 2012 Elsevier B.V.


Tanaka G.,Gunma Museum of Natural History | Naruse H.,Kyoto University | Yamashita S.,Chiba University | Arai K.,Chiba University
Geophysical Research Letters | Year: 2012

In Rikuzentakata City, Ostracode assemblages in sediment deposited by the Tohoku-Oki earthquake and tsunami of 11 March 2011 revealed that the sediment was derived from the seafloor from at least 9 m water depth, and was transported inland more than 1 km. The tsunami wave height at this location was higher than 10 m. Four hundred fifty seven modern ostracode assemblages were used in the modern analogue technique to estimate the depth source of the tsunami deposited assemblages. The application of this method to paleo-tsunami deposits may provide insight into past tsunami wave height and potentially earthquake slip and magnitude. Copyright 2012 by the American Geophysical Union.


Sugawara H.,Gunma Museum of Natural History | Sakakibara M.,Ehime University | Ikehara M.,Kochi University
Planetary and Space Science | Year: 2014

Microbial trace fossils on terrestrial basalts can be used as an analogue in the search for traces of life on other terrestrial planets. This study reports on microbial trace fossils within Permian greenstones in the Maizuru Terrane, southwest Japan, which is recognized as back-arc basin oceanic crust that consists mainly of metabasalt and metagabbro. The trace fossils have been studied by means of morphology, mineralogy, elemental mapping, and carbon isotope analysis. Although minute original textures of trace fossils are recrystallized in these rocks, Granulohyalichnus vulgaris isp., Tubulohyalichnus spiralis isp., and Tubulohyalichnus annularis isp. were identified. Significant concentration of C within the trace fossils implies these are organic remnants from microbes. The δ13CPDB values <-7‰ of calcite within the greenstones indicates that the bacterial activity took place prior to the formation of calcite veins. The results support that microbial trace fossils within low-grade metamorphic basalt can be reliably identified based on their morphology and chemical composition, as reveled by elemental mapping. In this context, glassy Martian basalt may be the best rock type to investigate in terms of searching for signs of microbial activity on Earth and other planets. © 2013 Elsevier Ltd.


Tanaka G.,Gunma Museum of Natural History | Komatsu T.,Kumamoto University | Saito Y.,Geological Survey of Japan | Nguyen D.P.,Vietnam Institute of Geosciences and Mineral Resources VIGMR | Vu Q.L.,Ai Mo
Marine Micropaleontology | Year: 2011

Eighty-five species belonging to 46 genera of Ostracoda were recovered from 169 samples in three sediment cores (VN, NB, and GA) from the Red River delta plain, northeastern Vietnam. From a Q-mode cluster analysis, we recognized three biofacies (Biofacies A, B, and C). Biofacies B is subdivided into Biofacies BI and BII. The environment of Biofacies A is interpreted as open marine, those of Biofacies BI and BII as marine to brackish water and brackish water, respectively, and that of Biofacies C as oligohaline to mesohaline brackish water. The Holocene sediments consist of estuarine sediments deposited under relatively high sea levels following transgression, deposited during 11-8.5cal kyr BP, overlain by deltaic sediments deposited under relatively low sea levels following regression, and the ostracod assemblages reflect these changes. The estuarine sediments of the early Holocene transgression are characterized by ostracod Biofacies BI. An erosional surface marks an abrupt change to the shelf environment, accompanied by sediment starvation. The interval around this surface, identified as the maximum flooding surface, is characterized by ostracod Biofacies A. During the subsequent delta progradation, the sedimentary environment changed from a prodelta to delta front, and then to a delta plain, and the corresponding ostracod assemblages changed from Biofacies A to BI, BII, and then C in ascending order. Taken together, our results show that the temporal changes in ostracod assemblages since 10. cal kyr BP are closely related to the evolution of the Red River delta system and can serve as good indicators of paleoenvironmental changes. © 2011 Elsevier B.V.


Maeda H.,Kyoto University | Tanaka G.,Gunma Museum of Natural History | Shimobayashi N.,Kyoto University | Ohno T.,Kyoto University | Matsuoka H.,Kyoto University
Palaios | Year: 2011

The Furongian Orsten-type fossil Lagerstätte in the Alum Shale Formation of Sweden is an extraordinary deposit known for its detailed, three-dimensional preservation of the soft parts of small animal carcasses which have been replaced by calcium phosphate and occur in organic-rich nodular limestone. The exact cause and mechanism of this unusual fossil preservation, however, particularly the source of phosphorus, which plays a key role, remains unknown. Detailed observation in the Agnostus pisiformis Zone in the Backeborg section (Kinnekulle district) reveals that the phosphatocopine crustaceans showing soft-part preservation occur only in a few thin (<3 cm) layers containing abundant fecal pellets (pellet beds). Development of cross lamination suggests that the pellet beds were formed by low density sediment-gravity flow. Orsten-type preservation has been attributed to high phosphate levels in global marine waters during the Cambrian period; however, wavelength-dispersive X-ray and X-ray diffractometry analyses reveal that the Orsten limestones and surrounding shale were generally poor in phosphorus, which was mostly concentrated in the fecal pellets. The small animal carcasses preserved in such deposits were phosphatized during early diagenesis owing to the high local phosphorus levels of the accumulated fecal pellets. Searches for such cesspool-type preservation may yield further discoveries of Orsten-type fossil Lagerstätten in other strata of various ages. Copyright © 2011, SEPM (Society for Sedimentary Geology).


Tanaka G.,Gunma Museum of Natural History
Fossils | Year: 2012

The Light-Switch Hypothesis' proposed by Parker (2003) is reviewed on the basis of recent relevant literature in order to test the hypothesis. This review revealed the following: 1) Diversification of bilaterian animals occurred during the Late Ediacaran Period, based on paleontological and molecular clock evidences. 2) Developmental genetic studies of eyes suggest that the eyes of bilaterian animals were formed from those of the Urbilateria, which hypothetically had both rhabdom and cilium photoreceptors during the Ediacaran period. During evolution, vertebrates utilized cilium photoreceptors, while invertebrates selected rhabdom photoreceptors for the development of eyes. On the basis of the detailed research of the ommatidium surface of the low-light adapted compound eye of the fruit fly, the phenotype of corneal nipple protuberances has changed in a extremely short time period from the view point of the geologic time scale. 3) The oldest fossilized eyes discovered are those of trilobite and bradoriid arthropods from 521 Ma. Increases in body size, and the corresponding increase of energy required, during 630 Ma - 521 Ma may have been triggered by the evolution of the eye.'.


Tanaka G.,Gunma Museum of Natural History | Matsushima Y.,Kanagawa Prefectural Museum of Natural History | Maeda H.,Kyoto University
Paleontological Research | Year: 2012

Forty-seven sediment samples were taken from a borehole core at Oppama Park, Yokosuka City, Kanagawa Prefecture, central Japan. Fifty-eight ostracod species, representing 32 genera, were identified in the 32 samples. Three ostracod biofacies (IIII) were identified using Q-mode cluster analysis. On the basis of ostracod biofacies, the following paleoenvironmental changes were recognized in the study area: land mudflat (no ostracods) → muddy bottom environment of inner bay (biofacies III) → sandy bottom environment of bay near rocky shore (biofacies II) → shallow mudflat (biofacies I). Modern analog technique (MAT) showed that the paleoenvironment of the study area was a warm (maximum bottom temperature in summer around 30°C; minimum bottom temperature in winter around 7°C) and shallow bay, similar to that around Honshu Island today. An ostracod specimen, Parakrithella pseudadonta, with exceptionally well preserved soft parts was discovered in one of the horizons, at a core depth of 20.420.5 m. In this horizon, an event deposit, namely, one indicating an increase in paleobathymetery, was identified from ostracod assemblages, which were identified as tsunami deposits on the basis of previous studies of neighboring areas. Similar soft part-preserved arthropod fossils have been discovered from the Upper Cambrian (500 Ma) of Sweden. Many fecal pellets have also been found in the Orsten limestone. Such "cesspools" were exceptionally phosphatized during early diagenesis owing to the high local phosphorus levels produced by the accumulated fecal pellets. The "cesspool preservation hypothesis" provides an explanation for this kind of exceptional fossilization, found in the marine sediment record from the Late Cambrian onward. © by the Palaeontological Society of Japan.


Tanaka G.,Kumamoto University | Parker A.R.,Natural History Museum in London | Hasegawa Y.,Gunma Museum of Natural History | Siveter D.J.,University of Leicester | And 12 more authors.
Nature Communications | Year: 2015

Vision, which consists of an optical system, receptors and image-processing capacity, has existed for at least 520 Myr. Except for the optical system, as in the calcified lenses of trilobite and ostracod arthropods, other parts of the visual system are not usually preserved in the fossil record, because the soft tissue of the eye and the brain decay rapidly after death, such as within 64 days and 11 days, respectively. The Upper Carboniferous Hamilton Formation (300 Myr) in Kansas, USA, yields exceptionally well-preserved animal fossils in an estuarine depositional setting. Here we show that the original colour, shape and putative presence of eumelanin have been preserved in the acanthodii fish Acanthodes bridgei. We also report on the tissues of its eye, which provides the first record of mineralized rods and cones in a fossil and indicates that this 300 Myr-old fish likely possessed colour vision. © 2014 Macmillan Publishers Limited.


Kimura T.,Gunma Museum of Natural History | Hasegawa Y.,Gunma Museum of Natural History
Journal of Vertebrate Paleontology | Year: 2010

A new, well-preserved mysticete fossil is described and diagnosed here as Joumocetus shimizui, gen. et sp. nov. The holotype specimen was recovered from the earliest Late Miocene, Haraichi Formation, Annaka Group, Gunma Prefecture, Japan. Although many cetotheres have been found from the Pacific realm, the Cetotheriidae sensu stricto is relatively rare in terms of taxonomic diversity and also abundance of specimens. Joumocetus will be the fourth genus of the Cetotheriidae sensu stricto from the Pacific and the geologically earliest and most archaic Cetotheriidae sensu stricto yet reported. Joumocetus retains a number of primitive characteristics, and our phylogenetic analysis indicates that Joumocetus is placed basally among the Cetotheriidae sensu stricto. Our analysis clearly indicates a monophyly of the Cetotheriidae sensu stricto and of a clade that consists of Balaenopteridae, Eschrichtiidae, and cetotheres. The results also indicate the monophyly of the following two groups: cetotheres not belong to Cetotheriidae sensu stricto (= Isanacetus-group) and Cetotheriidae sensu lato (= Isanacetus-group + Cetotheriidae sensu stricto); however, the monophylies of these groups are not well supported by bootstrap analysis. Consequently, the relationships and definition of these mysticete taxa remain unclear. Based on the present study and a review of previous studies, we suggest that the Isanacetus-group is a paraphyletic taxon that includes the ancestors of two clades, Balaenopteridae + Eschrichtiidae and the Cetotheriidae sensu stricto. © 2010 by the Society of Vertebrate Paleontology.

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