京都大学 / 新制・課程博士 / 博士(理学) / 甲第24428号 / 理博第4927号 / 新制||理||1704(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 佐藤 活志, 准教授 堤 昭人, 教授 田上 高広 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Beavers are members of Castoridae - the family of large rodents characterized by a robust skull of sciuromorphic type, a sciurognathous mandible, dentition with a tendency to hypsodoncy and incisives by uniserial microstructure. The aim of the thesis is a detailed morphometric analysis of the fossil material of beavers coming from the early Miocene (MN 3a) locality Ahníkov I, II in the Czech Republic. In the numerous material comprising 388 fragmentary specimens, all belonging to the genus Steneofiber, two distinct species were distinguished, attributed here as - Steneofiber eseri (the larger form) and Steneofiber aff. dehmi (the smaller form). Their taxonomy, systematics and assumed position within existing phylogenetic models were discussed. Key words: Castoridae, Steneofiber, Czech republic, Ahníkov, MN 3, early Miocene

The Late Hemphillian (latest Miocene or earliest Pliocene, 7-4.5 Ma) Gray Fossil Site in northeastern Tennessee is interpreted to represent a lacustrine paleokarst fed by a river or stream. This research focuses on the morphological and systematic relations of Nyssa endocarps (fruit pits) from the fossil site to extinct and extant Nyssa species. A combination of metric and nonmetric traits allows recognition of a new species: Nyssa grayensis sp. nov. This fossil species shares the most similarities with the extant Nyssa ogeche Bartram ex Marshall from southeast North America and the Eocene fossil Nyssa eolignitica Berry from western Tennessee. Affinities with Nyssa ogeche Bartram ex Marshall suggest a warmer winter climate than the present and periodically fluctuating water levels. Fossil vertebrates (Alligator, Heloderma, Hesperotestudo) and plants (Fossil relatives of Ilex vomitoria, Quercus virginiana, Taxodium, Acer leucoderme) with modern counterparts distributed in areas with mild winters support this interpretation.

The analysis of samples recovered from the abdominal area of an articulated tapir from the Late Miocene (4.5-7 million bp) Gray Fossil Site, revealed a rich palyno-fauna comprised of about 94% egg/oocyst-like structures and 6% pollen and other palynomorphs. In addition, a tight grouping of six hickory nuts (Carya) was recovered from the same area suggesting that the samples represent the abdominal contents. The analysis of a sample from immediately outside the tapir produced a sample with 98% pollen and less than 0.5% egg-like structures. The size, shape, and general morphology of egg-like structures were analyzed with light and scanning electron microscopy and were compared to a variety of intestinal eggs found in extant ungulates, and in particular the Perissodactyla. We also compared the fossil structures to the numbers and kind of intestinal parasites recovered from fecal samples from the Baird's tapir (Tapirus bairdii) in Costa Rica and from samples collected from the Lowland tapir (T. terrestris) from Ecuador to assess their similarity to our fossil sample. Based on these data we discuss what role parasites may have played in the biology of T. polkensis during the late Miocene-early Pliocene.

The preservation and quantity of fossil tapirs (Tapirus polkensis) from the Gray Fossil Site in northeastern Tennessee provides a unique opportunity for comparison and analysis of skeletal characters. Intraspecifically, modern tapirs show little to no variation in the morphology of the sagittal crest. However, several different morphologies exist within the sample at Gray. No osteological evidence of sexual dimorphism exists for tapirs, and no correlation between crest shape and sex was observed. Several juveniles display well defined crests, while some adults have only minor thickening of the temporal ridges; therefore, no distinct correlation between age and crest state could be established. Three different patterns of wear exist within the sample, but there is no correlation between these and crest morphology. No cranial pathologies were found to be associated with a crest type. Despite some correlations the sagittal crest could simply be a variable character due to intraspecific variation.

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Almost all sandstone beds occurring in the Upper Miocene formations at the Los Angeles basin were deposited by turbidity currents. Primary textures and structures indicative of turbidites occur in fair abundance throughout all three Upper Miocene formations. All accessible outcrops of the Puente, Modelo, and Upper Miocene portion of the Monterey and Capistrano Formations were scrutinized for sandstone beds containing primary sedimentary structures. Through study of these structures, the direction of current movement was determined. The pattern of current movement displayed reveals that sediment was being transported into the Los Angeles basin from all sides. Current directions and mineralogic studies indicate that essentially three source areas were supplying sediment into the basin. These source areas are 1) the San Gabriel Mountains, 2) an area to the east of the Santa Ana Mountains, and 3) a ridge of metamorphic rock paralleling the present coast line. The majority of sediment was derived from an area in the San Gabriel Mountains located northeast or the basin. This is evidenced by the fact that the thickness, grain size, and total sand content of the Upper Miocene units decrease southwestward across the basin.

Terrestrial carbon-isotope stratigraphy has proven a promising tool for stratigraphic correlation between the different exchangeable carbon-isotope reservoirs, as well as a powerful approach to reconstructing the evolution of δ13C of atmospheric CO2, which is closely associated with the evolution of palaeoenvironment and palaeoclimate. However, the limited understanding of pitfalls in specific application potentially restricts the method’s utility for stratigraphic correlation and palaeoenvironmental reconstruction. This thesis takes advantage of three case studies at two vital geological intervals which are both characterized by the significant carbon-isotope perturbation in the exchangeable reservoirs, to explore the nature of terrestrial carbon-isotope stratigraphy. Two of the case studies focus on the late Early to Middle Miocene, the period of the so called Monterey Event that is marked by remarkable positive carbon-isotope excursions in benthic and pelagic marine carbonate records. There are few terrestrial carbon-isotope records for the Monterey Event. In the present study, shallow marine sediments were collected from boreholes in the New Jersey margin, USA (IODP, Expedition 313) and North Sea Basin, Denmark. Phytoclasts are concentrated from palynological residues as the basis for a terrestrial carbon-isotope stratigraphy from the two locations. The carbon-isotope curves obtained can be correlated in detail locally, and correlated crudely on a global scale. However, there are no definite positive carbon-isotope excursions observed in the terrestrial isotopic stratigraphic records through the biostratigraphically determined Langhian interval equivalent to the Monterey Event. The reasons for the absence of relatively positive carbon-isotope excursions in terrestrial carbon-isotope stratigraphy might be caused by the reworking deposits of woody phytoclasts from older strata or some other process related to reworking. Another case study centres on the Triassic-Jurassic boundary and Early Jurassic fluvial and lacustrine succession in the Kuqa section, Tarim Basin, NW China. Macrofossil wood samples were collected to generate the terrestrial carbon-isotope stratigraphy. On the basis of the biostratigraphy and potential Stage/Age (sub-) boundaries implied by biological overturns, the terrestrial carbon-isotope stratigraphy in the Kuqa section can be well correlated with both terrestrial and marine carbon-isotope stratigraphic records from UK through the Early Jurassic. For the Triassic-Jurassic boundary, more precise correlation was made globally and an exact the position of Triassic-Jurassic boundary is proposed in the Kuqa section. In light of the biostratigraphy and the carbon-isotope stratigraphy obtained in the present study, an updated age assignment of the lithostratigraphic units is proposed to Age/Stage level in the Early Jurassic across the Northern Tarim Basin. The carbon-isotope stratigraphy thus significantly improves the terrestrial stratigraphic resolution. Terrestrial carbon-isotope stratigraphy is a powerful tool for global stratigraphic correlation and unifies stratigraphic correlation over marine and non-marine strata in cases when potential biasing factors are excluded.