Taxonomic and phylogenetic aspects of the shell ultrastructure of nine Cretaceous rhynchonellide brachiopod genera

Abstract

The shell ultrastructure of nine Cretaceous rhynchonellide brachiopod genera was studied using SEM with the purpose of finding additional criteria for the taxonomy and phylogeny of Late Cretaceous rhynchonellides. The genus Orbirhynchia is characterized by a coarse fibrous basiliolidine type structure of the secondary shell. The genera Cyclothyris, Cretirhynchia, Septatoechia, Belbekella, Lamellaerhynchia, Almerarhynchia, Burrirhynchia and Grasirhynchia have a fine fibrous rhynchonellidine type structure. An outline of some diagnostic characteristics for each genus is presented. Some diagenetic alterations of the shell, such as silicification and recrystallization are also discussed.