Haruyoshi Maeda

Upper Cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from Sakhalin, Russian Far East: A proxy for the isotopic composition of paleoatmospheric CO2

Abstract Time-stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from Cenomanian–Maastrichtian successions for the Russian Far East can be correlated to those of carbonate carbon from well-studied successions for other parts of the world. Age-indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in Japan and can be applied to the whole Cretaceous succession except for the Upper Cenomanian–Lower Turonian and the upper part of the Maastrichtian (zones lacking macrofossils). Globally correlative carbon isotopic events previously documented with carbonate carbon from Europe and with carbonate carbon and marine organic matter from the U.S. Western Interior are recognized with similar magnitude through uppermost Cenomanian–Lower Campanian. In ascending order these events are: positive ‘spike’ across the Cenomanian–Turonian boundary; step-like leveled segment followed by negative shift (Lower–Middle Turonian); trough-like negative excursion (Middle–Upper Turonian); positive rebound coupled with following broad peak (Coniacian); and positive peak (basal Campanian) followed by modest negative excursion. The parallel fluctuation of the δ 13 C value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric CO 2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of CO 2 in the ocean–atmosphere system. In the Upper Campanian and Maastrichtian, a negative δ 13 C excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from South and North Atlantic, the Indian, and the Pacific Oceans. Within this interval, the δ 13 C value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global CO 2 reservoir with relatively minor regional/local ‘noise’.

Taphonomic Features of a Lower Permian Beached Cephalopod Assemblage from Central Texas

Abstract A taphonomic investigation of a fossil assemblage near Coleman, Texas, U.S.A., has revealed a rarely seen part of the cephalopod taphonomic pathway. The cephalopods occur in a brown shale with a low-diversity, gastropod-dominated fauna that is mixed together with a conifer-seed fern-dominated terrestrial flora. All of the cephalopod shells (n=2000+) are damaged. The brown shale is interpreted as representing a brackish-water or quiet, muddy beach environment, based in part on the delicate three-dimensional preservation of the terrestrial plant debris and the absence of stenohaline benthic marine fauna. Most upper Paleozoic cephalopods (especially ammonoids) are thought to have lived in offshore (middle to outer shelf) environments. The environmental interpretation and the massive damage observed on the cephalopod shells support the interpretation that this cephalopod fauna has been transported from one or more distant offshore biotopes. These cephalopods had shells with positively buoyant conchs that floated after death onto the mud beach, where they were trapped in a Konzentrat fossil-Lagerstätte with the indigenous gastropod fauna and a well-preserved terrestrial flora. The significance of this taphonomic analysis is the documentation of a transported cephalopod fauna from an offshore biotope to a paleoshoreline environment. By studying the Coleman cephalopods, a specific criterion for assessing the type and degree of shell damage for beached fossil assemblages has been developed; e.g., predominance of fragmentary shells (Type D). The criterion can be used to evaluate the taphonomy of other cephalopod faunas around the world.

Cambrian Orsten Lagerstätte from the Alum Shale Formation: Fecal pellets as a probable source of phosphorus preservation

Abstract 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.

Stratigraphy and fossil bivalve assemblages of the mid-Cretaceous Goshoura Group, southwest Japan

ABSTRACT The mid-Cretaceous Goshoura Group, non-marine to shallow marine fossiliferous clastic deposits, is typically exposed on Goshoura Island, Amakusa, western Kyushu, Japan. Based on precise sedimentological analyses, the group is subdivided into the following three formations, the Eboshi, Enokuchi and Karakizaki Formations in ascending order. These formations are herein redefined, and the Eboshi and Enokuchi Formations are newly subdivided into members, i.e., the Eboshi Formation is composed of the Tanoshiri, Hobashiraiwa and Arakuchizaki Members, and the Enokuchi Formation consists of Hokahira and Gannohana Members. Geological age of the group is determined by age-diagnostic ammonite species, e.g., the Late Albian Mortoniceras cf. rostratum from the Hokahira Member, and the Early Cenomanian Graysonites adkinsi from the overlying Gannohana Member. Fifty-eight bivalve species belonging to 42 genera are identified from the group. These bivalve fossils are grouped into 7 fossil assemblages whose occurrences are closely linked with depositional facies. Several species occur as in life position in situ. Diversified Pterotrigonia are abundant in marine bivalve assemblages. Brackish-water bivalves such as Tetoria shishijimensis, Pulsidis higoensis and Crassostrea kawauchidensis repeatedly occur from tidal flat deposits at variable stratigraphic levels. The faunal diversity of the brackish-water assemblage increases from the estuarine deposits of the Eboshi Formation to the tidal-flat deposits on the shoreface of the Karakizaki Formation. These results in the Goshoura Group provide a new paleoecological scheme of the mid-Cretaceous bivalve fauna in the Far East Realm.

First discovery of Pravitoceras sigmoidale Yabe from the Yezo Supergroup in Hokkaido, Japan

Abstract An almost intact specimen of an uppermost Cretaceous heteromorph ammonoid, Pravitoceras sigmoidale Yabe, was recently discovered from the Hakobuchi Formation of the Yezo Supergroup in the Hidaka area, Hokkaido. The specimen is preserved in a lenticular calcareous nodule. It retains two whorls of planispiral phragmocone and a succeeding retroversal hook, which is associated with a lower jaw apparatus near the aperture. P. sigmoidale occurs within the Inoceramus shikotanensis Zone at the Hidaka section. Patagiosites alaskensis, Gaudryceras sp., Inoceramus shikotanensis, and Gigantocapulus problematicus cooccur with P. sigmoidale. The megafossil assemblage resembles those of the Upper Campanian-Lower Maastrichtian in the Sakhalin area. P. sigmoidale has a very short range assignable to the Upper Campanian. However, it has been assumed to be an endemic species of the Izumi Group in southwest Japan, and has never before been found from northeast Japan. Scarcity of common zone-indexing taxa is a bottleneck for biostratigraphic research of the uppermost Cretaceous System in Japan. The first discovery of P. sigmoidale from the Hidaka area is a significant step for much more precise biostratigraphic correlation between the Yezo Supergroup and the Izumi Group.

An exceptionally well-preserved Eocene dolichopodid fly eye: function and evolutionary significance

The exceptionally preserved eyes of an Eocene dolichopodid fly contained in Baltic amber show remarkable detail, including features at micrometre and submicrometre levels. Based on this material, we establish that it is likely that the neural superposition compound eye existed as far back as 45 Ma. The ommatidia have an open rhabdom with a trapezoidal arrangement of seven rhabdomeres. Such a structure is uniquely characteristic of the neural superposition compound eye of present-day flies. Optical analysis reveals that the fossil eyes had a sophisticated and efficient optical system.

Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish

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.

Exceptional Preservation Within Pleistocene Lacustrine Sediments of Shiobara, Japan

Abstract A new conservation Lagerstätte is described from the middle Pleistocene Shiobara Group of central Japan. The biota includes mammals, birds, amphibians, fish, insects, arachnids, flowers, abundant leaves, fungi, and bacteria preserved within laminites that were deposited in a lacustrine environment. Comminuted plant material in medium-grained, massive sandstones was deposited from high-density flows. This fragmentation of plant material probably indicates that it had decayed prior to transport. Plant and animal remains are largely nonfragmented and were thus transported prior to decay. The laminites are composed of rhythmic, millimeter-scale alternations of clay-to-silt-grade clastics with siliceous, diatom-rich layers. In the western part of the basin the diatoms are preserved as opal-A, but in the eastern part, where soft-part preservation is most common, they have been altered to opal-CT and form thin, white, porcelaneous layers with a lepispheric texture. Soft parts are preserved as carbon residues and microbial films, and although siliceous laminae enclose the fossils, permineralization of tissues is infrequent. Soft-part preservation was promoted by the self-sedimentation of aggregated mats of diatoms that shrouded the biota on the lakebed. This stabilized the carcasses and prevented them from being disturbed. It also prevented the diffusion of both the incoming nutrients and outgoing metabolic by-products between carcasses and surrounding water and may thus have promoted soft-part preservation. Silica cementation also inhibited the destruction of fossils by the intense weathering in the humid Japanese climate.

Original structural color preserved in an ancient leaf beetle

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.

Piggyback whorls: A new theoretical morphologic model reveals constructional linkages among morphological characters in ammonoids

A new theoretical morphological model is proposed for the analysis of growth, form and morphospace of ammonoid shells. In this model, the shape of a radial cross section through the shell is simulated by “piggybacking” of successive whorls. The “piggyback whorls model” is defined in terms of the enlarging rate of the perimeter and the proportion of the dorsal wall to the whorl periphery, if an isometric relationship is assumed between perimeter and area of the cross-sectioned whorl. Allometric coefficients on these growth parameters determine how compressed and evolute shells are formed. The present model successfully reproduced some correlations among purely geometric variables that have been reported in previous works and were also observed in our biometric analyses. This model yields a hypothesis of “constructional linkages” between aperture shape and coiling geometry that might provide a functional coupling between hydrostatic and hydrodynamic characters. The model may partly explain Buckmans Law of Covariation between rib features and shell shapes.