抄録
Two fossil shark teeth found from the laminated gray sandy mudstone of the uppermost part of the Middle Miocene (15 Ma) Yokoo Formation (Northern Fossa Magna Region) in Ueda-city, Nagano Prefecture, central Japan, were described. In comparison with Recent specimens, these were identified as teeth of gulper shark, Centrophorus sp.. This report is the first description of the genus Centrophorus from Japan. The uppermost part of the Yokoo Formation is mainly composed of alternation of sandstone and mudstone (rich in sandy mudstone) which grades upward into glauconite sandstone. Therefore judging from the habitat of the Recent genus Centrophorus, the lithofacies,the molluscan and benthic foraminifer fossils, it is estimated that the uppermost part of the Yokoo Formation was deposited on the shelf slope at depths between 700 and 1500 meters under the reducing conditions.
