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1.
Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships 总被引：1，自引：0，他引：1
Abstract Fossil pinnipeds in the extinct otariid subfamily Allodesminae are large, relatively highly evolved marine carnivores that became abundant and diverse in Middle Miocene time and were restricted to the North Pacific Ocean. Their record extends from early Middle Miocene through Late Miocene, with records from California, Oregon, Washington, Baja California and Japan. Allodesmines are characterized by extreme sexual dimorphism, a large orbit, retracted orbital margin of the zygomatic arch, a deeply mortised jugal-squamosal junction, wide palate, bulbous cheek tooth crowns, nearly flat tympanic bulla with wrinkled ventral surface, a large tympanohyal fossa, large ear ossicles and deep mandible. Eleven allodesmine species are known (eight of which are named), in at least four genera, and most belong to the typical genus Allodesmus Kellogg, 1922. The earliest and most generalized allodesmine known is from the early Middle Miocene (ca 16 Ma) Astoria Formation in coastal Oregon. The last known records are from Late Miocene rocks (ca 10 Ma) in California and Washington. New taxa proposed here are: the genus Brachyallodesmus Barnes and Hirota, to contain Allodesmus packardi Barnes, 1972; the genus Megagomphos Hirota and Barnes, to contain Allodesmus sinanoensis (Nagao, 1941); the species Allodesmus sadoensis Hirota, (Middle Miocene, Japan); the species Allodesmus megallos Hirota (Middle Miocene, Japan); and the species Allodesmus gracilis Barnes (Middle Miocene, California). Additionally, the genus Atopotarus Downs, 1956, and the species Allodesmus kelloggi Mitchell, 1966, are resurrected. Allodesmines were apparently a rapidly evolving group, and most appear to have been adapted to roles later filled by otariine, dusignathine and imagotariine otariids, and the Phocidae (true seals). They became extinct in Late Miocene time and left no living descendants. Although some of their characters evolved convergently with various living species of the pinniped family Phocidae, Allodesminae are an otariid group and not part of the evolutionary history of Phocidae. 相似文献
2.
Shigeo Miyazah Hideo Horkawa Naoki Kohno Kiyoharu Hirota Masaichi Kimura Yoshkazu Hasegawa Yukimitsu Tomida Lawrence G. Barnes Clayton E. Ray 《Island Arc》1994,3(4):361-372
Abstract The fossil pinniped record of the North Pacific Ocean includes both Phocidae and Otariidae ( sensu lato ), extends from the Late Oligocene to the Late Pleistocene, is taxonomically diverse, and is constantly becoming more complete owing to additional important discoveries. The earliest and most diverse fossil pinnipeds in the North Pacific are otariids, the phocids not appearing until the latest Pliocene. The theoretical center of otariid pinniped evolutionary history has been considered by some to be in the eastern North Pacific. New materials from the western North Pacific, however, including representatives of the subfamilies Enaliarctinae, Imagotariinae, Odobeninae and Otariinae, indicate that pinniped evolutionary patterns were basin-wide phenomena, and that a more complete record undoubtedly would reveal numerous trans-Pacific distributions. This would be expected considering the distributions of living species. The paucity of fossil Phocidae and their absence from pre-Pliocene deposits are consistent with theories that the family primarily evolved outside the North Pacific. 相似文献
3.
S. Hayakawa T. Kato T. Kohno K. Nishimura Y. Tanaka K. Yamashita 《Astrophysics and Space Science》1972,17(1):30-38
Cosmic X-rays in the energy range between 0.210 keV were observed with polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Sgr region and reached galactic latitudes of 50° and –90°. A new soft X-ray source was found in the Aries-Taurus region. The soft X-ray flux from the direction of NGC 1275 was conspicuous, whereas that of Sgr region source were very weak. The distribution of the intensity of diffuse soft X-rays over the scanned region indicates the galactic emission of soft X-rays. 相似文献
4.
Kotaro Kohno Koichiro Nakanishi Tomoka Tosaki Kazuyuki Muraoka Rie Miura Hajime Ezawa Ryohei Kawabe 《Astrophysics and Space Science》2008,313(1-3):279-285
Dense molecular medium plays essential roles in galaxies. As demonstrated by the tight and linear correlation between HCN(1–0)
and FIR luminosities among star-forming galaxies, from very nearby to high-z ones, the observation of a dense molecular component
is indispensable to understand the star formation laws in galaxies. In order to obtain a general picture of the global distributions
of dense molecular medium in normal star-forming galaxies, we have conducted an extragalactic CO(3–2) imaging survey of nearby
spiral galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). From the survey (ADIoS; ASTE Dense gas Imaging
of Star-forming galaxies), CO(3–2) images of M 83 and NGC 986 are presented. Emphasis is placed on the correlation between
the CO(3–2)/CO(1–0) ratio and the star formation efficiency in galaxies. In the central regions of some active galaxies, on
the other hand, we often find enhanced or overluminous HCN(1–0) emission. The HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) intensities are often enhanced up to ∼0.2–0.3 and ∼2–3, respectively. Such elevated ratios have never been observed
in the nuclear starburst regions. One possible explanation for these high HCN(1–0)/CO(1–0) and HCN(1–0)/HCO+(1–0) ratios is X-ray induced chemistry in X-ray dominated regions (XDRs), i.e., the overabundance of the HCN molecule in
the X-ray irradiated dense molecular tori. If this view is true, the known tight correlation between HCN(1–0) and the star-formation
rate breaks in the vicinity of active nuclei. Although the interpretation of these ratios is still an open question, these
ratios have a great potential for a new diagnostic tool for the energy sources of dusty galaxies in the ALMA era because these
molecular lines are free from dust extinction. 相似文献
5.
Keiji Misawa Mika Kohno Takayuki Tomiyama Takaaki Noguchi Tomoki Nakamura Keisuke Nagao Takashi Mikouchi Kunihiko Nishiizumi 《Earth and Planetary Science Letters》2010,289(1-2):287-297
Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ～ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 106 km2. Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 109 kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 109 kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere. 相似文献
6.
Abstract A nearly complete skeleton of a fossil sperm whale from the Middle Miocene age Bessho Formation at Shiga-mura, Nagano Prefecture, the most complete fossil physeterid skeleton found in Japan, is here named Scaldicetus shigensis, new species. Its abruptly tapered rostrum, deep supracranial basin, and high occipital crest are typical of physeterids. Large teeth with crenulate enamel on conical crowns, present in both the palate and mandible, are consistent with the genus Scaldicetus du Bus, 1867, a genus originally based on fossils discovered in the Antwerp Basin, Belgium. Scaldicetus shigensis is relatively primitive, having a relatively long, slender rostrum, large zygomatic arches, large tympanic bullae, prominent occipital condyles, low tooth count and a sloping occipital shield that is deeply emarginated laterally by large temporal fossae. The probable mandibular tooth count is 12, only one more than the primitive eutherian mammalian dentition. Despite its abundant primitive characters, Scaldicetus shigensis has very asymmetrical external nares, comparable to the living sperm whale, Physeter catodon, and is in this way more derived than most of the contemporaneous fossil physeterids. At a time when other sperm whales were more highly evolved, Scaldicetus shigensis retained a primitive occipital shield, large tympanic bullae, and low tooth count, as in primitive Oligocene odontocetes such as Agorophiidae. It was a relict form in Middle Miocene time, and provides an indication of a primitive stage of sperm whale evolution heretofore undocumented. Fossils from elsewhere previously referred to as Scaldicetus, largely on the basis of tooth characters, range in age from Early Miocene to Plio-Pleistocene time. Cranial material that would clarify relationships is lacking for most of these, and this time range seems too long for a cetacean genus. Because of this simplistic approach to identifications, Scaldicetus is probably a grade taxon, not a natural biological grouping. However, the tooth morphology of Scaldicetus shigensis is correct for the genus Scaldicetus, so we provisionally assign it to this genus. Redefinition of the genus Scaldicetus and revision of the Physeteridae are beyond the scope of the present study. 相似文献
7.
Eisuke Fujita Tomofumi Kozono Hideki Ueda Yuhki Kohno Shoichi Yoshioka Norio Toda Aiko Kikuchi Yoshiaki Ida 《Bulletin of Volcanology》2013,75(1):1-14
Crustal deformation by the M w 9.0 megathrust Tohoku earthquake causes the extension over a wide region of the Japanese mainland. In addition, a triggered M w 5.9 East Shizuoka earthquake on March 15 occurred beneath the south flank, just above the magma system of Mount Fuji. To access whether these earthquakes might trigger the eruption, we calculated the stress and pressure changes below Mount Fuji. Among the three plausible mechanisms of earthquake–volcano interactions, we calculate the static stress change around volcano using finite element method, based on the seismic fault models of Tohoku and East Shizuoka earthquakes. Both Japanese mainland and Mount Fuji region are modeled by seismic tomography result, and the topographic effect is also included. The differential stress given to Mount Fuji magma reservoir, which is assumed to be located to be in the hypocentral area of deep long period earthquakes at the depth of 15 km, is estimated to be the order of about 0.001–0.01 and 0.1–1 MPa at the boundary region between magma reservoir and surrounding medium. This pressure change is about 0.2 % of the lithostatic pressure (367.5 MPa at 15 km depth), but is enough to trigger an eruptions in case the magma is ready to erupt. For Mount Fuji, there is no evidence so far that these earthquakes and crustal deformations did reactivate the volcano, considering the seismicity of deep long period earthquakes. 相似文献
8.
Tsugunobu Nagai Masaynki Kuwashima Makoto Kawamura Tsuyoshi Kohno 《Planetary and Space Science》1979,27(7):1035-1037
It is suggested that the drop out of the 1.2–4 MeV proton flux, observed by the geostationary satellite GMS, was due to the Earthward shift of the particle boundary in all local time. The particle boundary motions are associated with substorm activities. 相似文献
9.
Y. Ueda K. Yamaoka J.E. Grove M. McCollough P. Durouchoux J. Rodriguez F. Mirabel J. Swank M. Feroci P. Casella A.J. Castro-Tirado C. Sánchez-Fernández S. Chaty H. Castaneda K. Kohno V. Dhawan S.A. Trushkin K. Ebisawa T. Kotani H. Inoue 《Astrophysics and Space Science》2001,276(1):25-28
We report results from multiwavelength observations of the microquasarGRS 1915+105 performed during the 2000 April campaign. This is one ofthe biggest campaigns ever made for this source covering the broadband from radio to γ-rays. Multiwavelength light curves compiledfrom all the data reduced up to date and broad band spectra obtainedwith ASCA and RXTE are presented. 相似文献
10.
Abstract Fossil otariid pinnipeds of the extinct genera Prototaria Takeyama and Ozawa, 1984, and Neotherium Kellogg, 1931, known from Middle Miocene deposits bordering the North Pacific Ocean, are small, primitive pinnipeds in the subfamily Imagotariinae. They have a small supraorbital process of the frontal or have lost it entirely, a three-rooted first molar, small paroccipital process, and ear morphology indicating that they belong in the subfamily Imagotariinae. Their unique derived characters include extreme intertemporal constriction and highly modified cheek teeth, the premolars having become molarized by the addition of protocones and lingual cingula. Prototaria Takeyama and Ozawa, 1984, the most primitive known imagotariine genus, contains two species, P. primigena Takeyama and Ozawa, 1984, and P. planicephala Kohno, 1994, both of early Middle Miocene age from Japan. Prototaria has a few derived characters, including a large antorbital process, narrow intertemporal region, and large orbit, but its primitive characters apparently were inherited from enaliarctine ancestors. The long enigmatic Neotherium mirum Kellogg, 1931, of Middle Miocene age from California, USA, is related to Prototaria, but differs by having an elongate skull, very slender zygomatic arch, ventrally exposed median lacerate foramen, and smaller but more molarized premolars. A more primitive new genus and species, Proneotherium repenningi Barnes, related to N. mirum, is from the early Middle Miocene Astoria Formation, coastal Oregon, USA. It shares some derived characters with Prototaria, and shares many other important derived characters with N. mirum. Imagotariines probably arose from some species of Early Miocene enaliarctines, became diverse in Middle and Late Miocene time, and are only known from the North Pacific realm. Although they might include the ancestors of true walruses of the subfamily Odobeninae, no known imagotariines appear to have been adapted for mollusk feeding as are the highly evolved modern walruses. Instead, imagotariines appear to have retained a primitive piscivorous diet, as did the fur seals and sea lions of the subfamily Otariinae. 相似文献