Cooperina (Productida, Brachiopoda) from the Lower Permian of Japan

Cooperina is a minute, very distinctive productid brachiopod belonging to the Family Cooperinidae Pajaud, 1968. This genus was established by Termier et al. (1966) with Cooperina inexpectata Termier, Termier and Pajaud, 1966, from the Word Formation of the Glass Mountains, West Texas, USA, as type species. At that time, Termier et al. considered the genus as a possible ancestor of the Triassic–Recent thecideid brachiopods (Superfamily Thecideoidea Gray, 1840, Order Thecideida Elliott, 1958). Later, Cooper and Grant (1969, 1975) considered Cooperina as a genus of the Superfamily Aulostegacea Muir-Wood and Cooper, 1960, Suborder Productidina Waagen, 1883, based on well preserved material from the lower to middle Permian of West Texas. More recently, Waterhouse (2002) grouped Cooperina into the Superfamily Cooperinoidea Pajaud, 1968 within the Suborder Productidina. Five species of Cooperina have thus far been described from the lower to middle Permian of the United States, Venezuela and Thailand: Cooperina inexpectata, from the Wordian of West Texas (Termier et al., 1966; Pajaud, 1968; Cooper and Grant, 1975) and from the Roadian to Wordian of Venezuela (Hoover, 1981); Cooperina parva Cooper and Grant, 1975, from the upper Wolfcampian to the uppermost Leonardian of West Texas (Cooper and Grant, 1975); Cooperina subcuneata Cooper and Grant, 1975, from the uppermost Leonardian of West Texas; Cooperina triangulata Cooper and Grant, 1975, from the lower Wolfcampian of West Texas; and Cooperina polytreta Grant, 1976, from the upper Kungurian–Roadian Ratburi Limestone of southern Thailand. This paper presents the first description of Cooperina from Japan. The specimens, described here as C. inexpectata and Cooperina nipponica sp. nov., were collected by the second (Y. M.) and third (Y. O.) authors from the lower part of the Nabeyama Formation (Parafusulina yabei Zone, Kungurian) of Yamasuge (Loc. KY4 of Tazawa et al., 2012), Kuzu area, Ashio Mountains, central Japan (Fig. 1). The material was prepared by separating the silicified fossils from some limestone blocks by using formic acid (3–4%). The occurrence of Cooperina from the Kuzu area supports the Permian palaeogeography of the Yamasuge fauna as described by Tazawa et al. (2010, 2012), who suggested that the Nabeyama Formation was deposited in an equatorial region of Panthalassa during the early Permian (Kungurian), proximal to what is now West Texas. All of the specimens described below are registered with the prefix KFM and housed in the Kuzu Fossil Museum, Kuzu, Sano City, Tochigi Prefecture, central Japan.