ABSTRACT
Among the genera of Mesozoic rhynchonellids more than 1600 species (including subspecies) are now placed in over 220 genera, about one fifth tentatively. The unequal size of genera is due partly to the working style of researchers and partly to the notorious problem of defining taxa unambiguously. In only a few instances does the size of the genus seem to reflect phylogeny. The life span of most Mesozoic rhynchonellid genera covers one to three stratigraphic stages. For long duration genera, up to 10 stages duration denotes their supposed conservative nature. Some paleogeographic implications, e. g. occurrence or migration pattern, are herein considered taxonomically. Mesozoic rhynchonellids assigned to a genus outside ‘Rhynchonella’” sensu lato, contain up to 90–95% of the revised species worldwide, and are just a part of the species which have been named in the last 150 years. Rhynchonnelid genera herein are organised according to species density.
