Vol.23 No.1

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A star-shaped trace fossil here assigned to Asteriacites quinquefolius (Quenstedt) was found in the Miocene Shirahama Formation, Wakayama Prefecture. This is the first report in Japan and stratigraphically youngest record for the ichnospecies. The fossil has five distinct arms and wide striations on both lateral sides of each arm, and the shape is bilaterally symmetrical. To clarify the fossil producing process, we conducted burial experiments of extant asteroids in aquaria and in situ for the first time. Asteroids buried themselves in the substratum using the tube-feet, and when asteroids were covered with thin sand, they escaped slantingly upward onto the sand tilting their body in a bilaterally symmetrical posture. As a result, the remaining trace was very similar to the fossil of A. quinquefolius from the Shirahama Formation. Accordingly, the results suggest the present fossil was formed by the behavior of escaping from thin sand cover by asteroids.

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In order to recognize and verify the lower Miocene deposits and the Aquitanian-Burdigalian boundary, benthic foraminifera from different localities in the north of the Central Iran Zone are considered. These facies-controlled foraminifera are useful for biostratigraphical studies, especially in the absence of planktic foraminifera. We investigated eleven stratigraphic sections of the north and northwest Central Iran Zone, and found datum levels of benthic foraminifera such as Borelis melo curdica, Peneroplis farsensis, Elphidium sp. 14, Meandropsinaanahensis, Meandropsina iranica, and Austrotrillina howchini. The most significant event is the first occurrence of Borelis melo curdica which appears at the beginning of the Burdigalian. Hence, this datum can be helpful to recognize the Aquitanian-Burdigalian boundary.

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A new deep-sea shark of the genus Scymnodalatias (Squaliformes, Somniosidae), S. kazenobon sp. nov., is described from the middle Miocene Yatsuo Group in Central Japan. This is the first fossil record of the genus Scymnodalatias from the Miocene strata and its first occurrence in the Pacific region. This discovery seems to indicate that major distributional changes occurred in the Pacific region sometime during the late Cenozoic era.

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Carboniferous and Permian limestones, as well as pre-Cretaceous cherts and basaltic volcaniclastic and volcanic rocks, are tectonically intermingled with lower Jurassic to upper Cretaceous siliciclastic rocks in the Yura area, Southern Chichibu Terrane of the western part of Kii Peninsula, Japan. They are seamount originated and highly fossiliferous. Fifty species assignable to 26 genera of Carboniferous foraminifers were distinguished from the limestone blocks in the Yura area (Kaimori, Tatego, and Shirasaki). Among them, 21 species assignable to 11 genera are systematically described, including two new species (Akiyoshiella kaimoriensis and Semistaffella vachardi). Foraminiferal biostratigraphic constraints on the limestone blocks result that the Kaimori block ranges from the middle Bashkirian to Kashirian and the Tatego blocks from the Visean/Serpukhovian to upper Serpukhovian or partly to Bashkirian, while a part of the Shirasaki block, from which the Carboniferous was first distinguished, is lower and middle Kasimovian. Characteristic species are Akiyoshiella kaimoriensis, Profusulinella prisca, and Bradyina nautiliformis in Kaimori; Eostaffella mosquensis and Bradyina sp. A in Tatego; and Protriticites variabilis, Obsoletes burkemensis, and Montiparus matsumotoi in Shirasaki.

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This study describes the right upper postcanine teeth of a single individual of a Pleistocene rhinocerotid (Mammalia, Perissodactyla) from the lower to lower Middle Pleistocene Kamo Formation of the Kokubu Group in Aira City, Kagoshima Prefecture, southwestern Japan. These teeth are heavily worn and are identified as P2-M2 with missing M1. They are identified as an indeterminate genus and species of the Rhinocerotidae, although they were previously identified as Rhinoceros aff. sinensis. These dental fossil specimens and the rhinocerotid footprints from the lower to lower Middle Pleistocene of Japan indicate that rhinocerotids certainly existed in Japan during the early to early Middle Pleistocene.

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A possible phylogenetic relationship of two species of Hyphantoceras (Ammonoidea, Nostoceratidae) was proposed, based on newly found specimens with precise stratigraphic occurrences in the Kotanbetsu and Obira areas, northwestern Hokkaido. Two closely related species, Hyphantoceras transitorium and H. orientale, were recognized in the examined specimens from the Kotanbetsu and Obira areas. Specimens of H. transitorium show wide intraspecific variation in the whorl shape. The stratigraphic occurrences of the two species indicate that they occur successively in the Santonian-lowermost Campanian, without stratigraphic overlapping. The similarity of their shell surface ornamentations and the stratigraphic relationships possibly suggest that H.orientale was derived from H. transitorium. The presumed lineage is likely indigenous to the northwestern Pacific realm in the Santonian-earliest Campanian. Hyphantoceras venustum and H. heteromorphum might stand outside a H. transitorium-H. orientale lineage, judging from differences of their shell surface ornamentation.