The occurrence of giant bivalve Alatoconchidae from the Yabeina zone (Upper Guadalupian, Permian) in European Tethys

The Permian gigantic bivalve family Alatoconchidae forms a member of the tropical shallow marine fauna intimately associated with the Tethyan warm-water-adapted Verbeekinidae fusulines, such as Neoschwagerina and Yabeina. The Velebit Mountains in central Croatia is one of the nine areas in the world that yielded Alatoconchidae, as first reported early in the 1970 s. In addition to the Neoschwagerina Zone (Wordian, Middle Guadalupian) originally described, we newly found Alatoconchidae from the Yabeina Zone (Capitanian, Upper Guadalupian) from the Brušane area in the central Velebit Mountains. Alatoconchidae occur in three stratigraphic levels of the Velebit Formation composed of black fusuline/algal wackestone/packstone with Yabeina. Although fragmented, the Alatoconchidae shell reach sizes over 40 cm long, and possess unique morphology with a lateral flange plus a prominent prismatic external layer in the double-layered shell structure. Our results confirm, for the first time in Europe and thus in the western Tethyan domain, that the stratigraphic range of the gigantic bivalve family extends up to the Capitanian as well as in the superocean Panthalassa. As no occurrence has been reported from the overlying Lopingian (Upper Permian), Alatoconchidae likely became extinct globally at the end of the Guadalupian, i.e., through the Guadalupian–Lopingian boundary mass extinction.