Archaeoradiolites, a new genus from the Upper Aptian of the Mediterranean Region and the origin of the Rudist Family Radiolitidae

Abstract

Archaeoradiolites gen. nov. (Radiolitidae), mainly
characterized by radially arranged branching walls structuring
the outer shell layer, includes two species, Archaeoradiolites
primitivus gen. et sp. nov. and Archaeoradiolites
hispanicus gen. et sp. nov. (type species), the distinction of
which is based on size, shell habit and development of the
radially branching microstructure. Their geographical distribution
is restricted to south-east Spain and south-west
France, i.e. the Western European Tethyan margin, whereas
data from the Black Sea coast of Turkey suggest a possible
extension to the Eastern European Tethyan margin. Each
species has a distinct biostratigraphic distribution within
the Upper Aptian (mainly the Gargasian). Agriopleura is
suggested to be the direct ancestor of Archaeoradiolites,
which in turn is considered as the progenitor of Eoradiolites.
The onset of the Radiolitidae is associated with global
oceanic changes that favoured calcite as opposed to aragonite
biomineralization. The acquisition of a porous shell
microstructure appears, in many respects, biologically
advantageous and may account for gaining a rapid
(< 1 myr) ecological ability for efficient colonization and
occupation of space of the family in the earlier phase of its
radiation.