Vol.24 No.1

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The octoradiate Eoandromeda Tang et al. from the Ediacaran of South China and South Australia is poorly understood and there are different interpretations of its morphology and paleoecology. The carbonaceous compression known as Eoandromeda, which is collected in black shales of the upper Doushantuo Formation in northeastern Guizhou, South China, shows various patterns and complex structures. Eoandromeda is interpreted as an umbrella-shaped metazoan, with a dome-shaped polar structure on the top of its body, eight dextrally spiraling arms and tapering skirts. The spiral arms are differentiated into a main segment consisting of rigid and thick masses and a distal segment consisting of flexible and thin masses. Thus, we consider that the spiral arms may have consisted of gelatinous masses and primarily grew in their distal segments (approximately the tapering skirts). The numerous feather-like structures on the platy spiral arms are regularly arranged into two longitudinal rows. We believe that Eoandromeda lived in a primitive “Seabed Grassland” with an abundance and diversity of macroalgae and was capable of swimming in the water column by flapping its feather-like structures. Based on measurements of the maximum diameter of the disk-shaped compression and the maximum width of the spiral arms, Eoandromeda can be divided into a juvenile stage (< 10 mm diameter) that has not been found, an adult stage (10–30 mm diameter) with a high growth rate in the width of the spiral arms, and a senescent stage (> 30 mm diameter) with a slow growth rate in the width of the spiral arms. Fully grown Eoandromeda, with thick and rigid spiral arms, may have mostly stayed on the sediment surface, temporarily swimming to seek new habitat or prey. The juveniles, better swimmers, may have had a soft body with soft and thin arms, unlikely to be preserved, and may have been easily transported by water currents.

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The late early to middle Miocene limestone bodies in the Sagara and Izu Peninsula areas of central Japan are reefal deposits that were deposited under a tropical climate and provide a window into the paleodiversity of tropical volcanic islands in the northeastern Philippine Sea Plate. Specimens from the early middle Miocene Megami Limestone in the Sagara area and from the middle Miocene limestone blocks within the Yugashima Group on the Izu Peninsula are described as Turbo (Marmarostoma) histrioides sp. nov. and Turbo (Marmarostoma) izuensis sp. nov., respectively. Discovery of these two new species raises the number of Marmarostoma species from four to six in the Sagara and Izu Peninsula areas, demonstrating that the subgenus was more diverse in the northeastern Philippines Sea Plate during the middle Miocene than it is today. In particular, there are double the number of Marmarostoma species (four species) from the middle Miocene in the Izu Peninsula compared with the modern fauna on the tropical islands of the Izu-Ogasawara Arc. The highest richness of modern species of Marmarostoma is found in the central Indo-West Pacific, where molecular phylogenetic studies have suggested that the subgenus rapidly diversified in the late Oligocene or early Miocene. Nevertheless, Miocene species of this subgenus are sparse in the central IWP, being incongruent to the diversity pattern expected from the molecular studies. The findings reported herein provide an insight into the origin of the central IPW biodiversity hotspot.

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Newly collected graptolites from the Co To Formation, Co To archipelago, NE Vietnam, comprise assemblages indicative of two biostratigraphical levels within the lower Silurian, Llandovery Series, Telychian Stage: the co-occurrence of Spirograptus turriculatus and Torquigraptus proteus? suggests an interval most likely within the upper part of the Spirograptus turriculatus Biozone or ‘Monograptus’ crispus Biozone, whilst Oktavites spiralis and Monoclimacis cf. subgeinitzi identify the Oktavites spiralis Biozone. The graptolites provide important biostratigraphical evidence for the age of the upper part of the lower Co To Formation, biostratigraphical ties between the NE Vietnamese succession of the Bac Bo Region and graptolite assemblages of the Long Dai Formation in the Viet-Lao Region of central Vietnam, and include the new species Monograptus hamulus sp. nov. co-occurring with S. turriculatus, which is perhaps an ancestral form to the later Telychian species Monograptus drepanoformis. We also report the first chitinozoans, including Belonechitina, from the Co To Formation.

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A new species of Nyanzachoerus (Mammalia, Artiodactyla, Suidae, Tetraconodontinae), Nyanzachoerus nakaliensis, is described on the basis of gnathodental specimens from the basal upper Miocene Nakali Formation (ca. 10 Ma) of central Kenya. Ny. nakaliensis is characterized by a lower crown height and relatively weaker furrows of the molars and proportionally larger P3–P4 compared to M3 among the species of the genus. It is the oldest and morphologically most primitive species of the genus. It shows close morphological similarities of the dentition with the Pliocene Asian tetraconodontine genus Sivachoerus, implying a possible closer phyletic relationship of Sivachoerus prior with Ny. nakaliensis rather than with Nyanzachoerus tulotos or Nyanzachoerus devauxi. This phyletic relationship implies a possibility that S. prior diverged from a stock of Ny. nakaliensis during the early late Miocene (Tortonian) in East Africa and then the lineage moved from East Africa to Asia. Finally, it should be stressed that there seems to be a problem of the paraphyly of the genus Nyanzachoerus.

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A primitive sawfly, Madygella humioi sp. nov., belonging to the family Xyelidae (Hymenoptera: Symphyta), is newly described from the Upper Triassic Mine Group, Yamaguchi Prefecture, southwest Japan. The new species differs from the five previously known Madygella species in having a cell length of 1r plus 2r shorter than that of 3r + 4r and a cell height of 3r + 4r lower than 2r plus pterostigma in a forewing. To date, this is the oldest fossil record of sawflies in East Asia. Regarding genus Madygella, this is the first example found outside of the Kyrgyz Republic. This discovery provides an insight into the early evolution of the order Hymenoptera and suggests a widespread distribution of the pioneering genus Madygella during the Triassic period.

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Mid-Cretaceous ammonoids, Euhystrichoceras nicaisei, Mantelliceras japonicum, and Hypostlingoceras japonicum were collected from float rocks probably derived from the middle part of the Miyanohara Formation in the Sakawa area, Shikoku, southwestern Japan. Although it has been suggested that the stratigraphic correlation of this formation based mainly on bivalves such as trigoniids needs to be reexamined, the occurrence of these ammonoids confirms that the middle part of the Miyanohara Formation is correlated to the lower Cenomanian. The results of this study support the suggestion that the shallow marine deposits of the mid-Cretaceous that contain similar molluscan faunas are widely distributed throughout the northwestern Pacific region.