First record of Plesiodiceras (Bivalvia, Hippuritida, Epidiceratidae) from the late Kimmeridgian (Late Jurassic) of Saudi Arabia, and its palaeobiogeographic significance

An allochthonous rudist horizon from the upper (?) Kimmeridgian Jubaila Limestone, central Saudi Arabia, is reported, which occurs northwest and south of Riyadh in equivalent stratigraphic position. The fossil assemblage is composed of abundant, densely packed to loosely spaced individuals of Plesiodiceras sp. (family Epidiceratidae) associated with rare stromatoporoids and gastropods. The fossil horizon has a continuous lateral extent of more than 10 km in its northern exposure. Its presence confirms the interpretation of the upper part of the Jubaila Limestone as a shallow marine unit, including deposits of back barrier lagoonal carbonate. This is the first record of Jurassic rudists from Saudi Arabia, and the first record of Plesiodiceras and the family Epidiceratidae from the southern margin of the Neo-Tethys and from Gondwana. Obviously, the broad tropical and subtropical shelves and shallow epicontinental seas of the Late Jurassic provided suitable habitats for the Epidiceratidae, both in Eurasia and Africa, and facilitated wider dispersal of the group than previously documented.