Paleontological Research

It has been suggested that the pseudopodia of radiolarians play a role in controlling buoyancy for floating behaviour. To understand the function of pseudopodia in terms of planktonic capability, we performed culture experiments on the flat-shaped radiolarian Dictyocoryne. A glass cell, a stereomicroscope and an X-Y-Z stage were used to observe the behaviour of Dictyocoryne from a lateral view. Under static conditions, Dictyocoryne grounded on the bottom of the glass cell extended pseudopodia from both sides of the flat disc surface. Subsequently, these individuals rose slightly by a length equal to that of the extended pseudopodia but remained attached to the bottom. These results suggest that Dictyocoryne lacks the ability to surface by obtaining buoyancy through the emergence of pseudopodia. Under conditions of convection flow, Dictyocoryne moved in the downstream direction only when pseudopodia were completely extended. When the convection flow moved upward, the individuals moved with the flow to just under the surface. In addition, convection flow changed the direction of a long, thick pseudopodium, called the axoflagellum, to be parallel with the flow. Consequently, the axoflagellum was always oriented towards the downstream side, being the disc face in the axoflagellum side on the upturn. Given that the flat-shaped spumellarians have symbiotic algae inside their cells, their unique planktonic capability leads to the stable efficiency of the algal photosynthesis.

Sedimentary sequences obtained from drilling during Integrated Ocean Drilling Program (IODP) Expedition 320/321, “Pacific Equatorial Age Transect (PEAT)” at eight sites (Sites U1331–1338) in the equatorial Pacific offer an ideal record for reconstructing the evolution of the ocean/climate system throughout the Cenozoic. The sediments drilled at Site U1335 record short-term events of paleoceanographic significance, including the early Miocene climatic optimum (MCO) and the middle Miocene climatic transition (MMCT). Abundant well preserved radiolarians were recovered from the lower Miocene radiolarian Zone RN2 through middle Miocene Zone RN5 at IODP Site U1335. A total of 46 radiolarian datum levels consisting of 20 first occurrences (FOs), 25 last occurrences (LOs), and one evolutionary transition (ET) was recognized within the studied interval at Site U1335. Of these datum levels, 36 radiolarian datum levels were directly tied to the geomagnetic polarity time scale (GPTS) across the early/middle Miocene boundary. The general magnitude of evolutionary change was estimated based on the total turnover rate (the sum of FOs and LOs per 0.5 m.y.) of tropical radiolarians, and two minor faunal turnovers of radiolarian species were recognized between 16.5 and 14.7 Ma and between 13.9 and 13.4 Ma. These faunal turnovers were associated with regional environmental changes such as the increased biological productivity in the equatorial Pacific during the MCO and the MMCT.

The Guadalupian (Permian) Gufeng Formation, distributed over the north margin of the South China block, is characterized by siliceous rock and muddy rock and yields several representative radiolarian fossils. The lithostratigraphy, radiolarian occurrences and biostratigraphy, and geochemical characteristics of the Gufeng Formation are reviewed and summarized in this paper. The distributional area of the Gufeng Formation is subdivided into the Lower, Middle, and Upper Yangtze regions. The Gufeng Formation in the Lower Yangtze region is lithostratigraphically characterized by muddy rock, chert, and nodule-bearing muddy rock in descending order. The Gufeng Formation in the Middle Yangtze region is lithostratigraphically characterized by chert, muddy rock with carbonate, and muddy rock in ascending order. The lithostratigraphic characteristics of the “Gufeng Formation” in the south margin of the South China block greatly differ from the typical Gufeng Formation in containing fewer siliceous rocks and a large amount of clastic rocks and in having a significantly greater total thickness; therefore, this article considers that the “Gufeng Formation” in the block's south margin should be isolated from the Gufeng Formation in the block's north margin. The radiolarian biostratigraphy of the Lower and Middle Yangtze regions is composed of the Pseudoalbaillella globosa, Ps. monacantha, and Follicucullus scholasticus-Ruzhencevispongus uralicus assemblage zones in ascending order. The lower Gufeng Formation has abundantly yielded the Albaillellaria; however, its occurrence ratio with respect to other radiolarian orders decreases stratigraphically upward. The geochemical characteristics indicate the following facts: (1) the siliceous rocks are generally biogenic; (2) even though a previous study concluded that the organic matter within the chert was originated from terrestrial or reworked organic matter, the origin remains debatable; and (3) the Gufeng Formation was formed on a continental shelf. The geochemical characteristics, in addition to the lithological characteristics, indicate that the redox conditions of the Gufeng Formation in the Lower Yangtze region changed from aerobic to suboxic to anoxic, while that in the Middle Yangtze region changed from oxic to anoxic to suboxic.

A new radiolarian genus, Ganjiangmoyea gen. nov., was discovered from the Lopingian (upper Permian) of the Yutouling section, Xiaodong area, Guangxi Zhuang Autonomous Region, South China. Ganjiangmoyea includes one new species (G. conica gen. et sp. nov.) and one possible new species (G.? striata gen. et sp. nov.). This new genus is characterized by numerous, swordlike radial spines extending from a central test. Single spines, presumably detached from the central test, co-occur with the Ganjiangmoyea species. Owing to these characteristics, Ganjiangmoyea could be placed under the family Oertlispongidae Kozur and Mostler. Paroertlispongus Kozur and Mostler and Pararchaeospongoprunum Lahm, belonging to the Oertlispongidae, also occur in the Permian, but their spines are bipolar and are not easily detached from the central test. Some of the Oertlispongidae genera, which occur abundantly in the Middle Triassic, also possess easily detached spines. Ganjiangmoyea might belong to a lineage of the Oertlispongidae that differs from that of Paroertlispongus and Pararchaeospongoprunum.

The Nadanhada terrane of northeastern Heilongjiang, northeastern China is composed of Jurassic accretionary complexes (i.e., the Yuejinshan Complex in the west, the Raohe Complex in the east) and succedent cover beds. In this paper we report two radiolarian assemblages recognized from four black claystone samples collected from the Dalingqiao Formation in the Dajiashan area of the Raohe Complex. The Striatojaponocapsa synconexa-“Tricolocapsa” tetragona assemblage of one sample consists of eleven species in eight genera, which indicates a middle Bathonian (Middle Jurassic) age, i.e., correlative with the uppermost Striatojaponocapsa plicarum Zone to the lower Striatojaponocapsa conexa Zone. The other three samples contain 34 species in 25 genera, which indicate a late Oxfordian–early Tithonian (Late Jurassic) age. The discovery of the Late Jurassic radiolarian assemblage indicates that the Raohe Accretionary Complex was formed during the Late Jurassic. The succedent late Tithonian–early Valanginian Buchia fauna-bearing Dong'anzhen Formation may be the earliest cover beds overlying the Raohe Accretionary Complex. Then, during the Early Cretaceous, the Nadanhada terrane received the deposition of the Aucellina bivalve fauna-bearing Dajiashan Group. This indicates paleogeographic differentiation between the Nadanhada terrane and the Tamba-Mino-Ashio terrane.

A metric analysis of the morphology of two related Eocene species (Podocyrtis sinuosa and P. mitra) that are part of the Lampterium evolutionary lineage was undertaken in order to evaluate hypotheses related to their mutual taxonomic distinction statistically. All analyses (landmark, outline semi-landmark and landmark-constrained outlines) support an interpretation of statistically significant species-specific shape differences. Moreover, landmark and semilandmark-based morphometric characterizations can be used to identify which regions of the test are best suited for making reliable taxonomic distinctions. These results suggest that both abdomen and thorax shapes represent species-specific characters. While this agrees, in part, with previous, qualitative diagnoses, our results shed light on precisely how abdomen and thorax shape differ between these species. In addition, our investigation demonstrates the taxonomic value of a morphometric approach to character analysis as thorax shape differences had gone unnoticed by previous investigators.

Disarticulated fossil euryalid ophiuroid vertebrae from the Middle Pleistocene Miyata Formation, Miura, Kanagawa Prefecture, eastern Japan, are described. The vertebrae are assigned to the family Gorgonocephalidae on the basis of arm branching and the presence of an open oral groove along the entire arm. This is the first record of fossil euryalids from the Indo-Pacific region.

Limnobiophyllum expansum (Lemnoideae, Araceae) was newly found in the lower Miocene (18.4–17.0 Ma) Hiramaki Formation of the Mizunami Group in the Kani Basin, Gifu Prefecture, central Japan. This genus was distributed widely in the Northern Hemisphere from the Late Cretaceous to the Paleocene, but a Miocene descendant (L. expansum) was reported only from Europe, in the Bohemian Basin, Czech Republic (early Miocene), Paldau, Austria (late Miocene), Schrotzburg, Switzerland (late Miocene) and Sośnica, Poland (late Miocene). Our finding is the first record of a Miocene Limnobiophyllum from an area other than Europe. The aquatic flora of Japan during the early Miocene is poorly documented, but this finding suggests a link between the aquatic floras of Europe and Asia.

Two early Carboniferous brachiopod species, Levitusia humerosa (Sowerby) and Grandispirifer mylkensis Yang, are described from Japan for the first time. These species, from the middle part of the Arisu Formation in the Okuhinotsuchi area, South Kitakami Belt, indicate an early Visean age. Therefore, the middle part of the Arisu Formation is correlated with the lower Visean. In terms of palaeobiogeography, occurrence of the two species suggests that South Kitakami was probably the eastern extension of the North China Province, and located near and to the east of North China (Sino-Korea) during the early Visean.