First record of a primitive radiolitid rudist from Japan

摘要: Abstract A radiolitid rudist, Eoradiolites cf. gilgitensis is described from a late early to Aptian shallowmarine limestone block in the lower part of Yezo Group, central Hokkaido, northern Japan. The Hokkaido characterized by compact (non-cellular) outer shell layer, as seen E. (from Iran, Afghanistan, Pakistan, and India), griesbachi Afghanistan), ngariensis western Tibet China), which are all located Southwest Asian region Tethyan margin. This one earliest records world primitive radiolitids with radiolitiform myocardinal arrangement. finding demonstrates that had already expanded Pacific at an evolutionary stage, faunal connection between northwestern Asia existed least Aptian.