Generic longevity of articulate brachiopods in relation to the mode of stabilization on the substrate
Abstract The geologic ranges of the articulate brachiopod genera which appear in the Treatise are converted into numerical values with the aid of radiometric dates on the Phanerozoic time scale. Longevity—frequency distributions are plotted for the genera segregated according to their mode of stabilization on the substrate. The categories and their subdivision for the mode of stabilization include: (1) anchorage by spines, (2) cementation (early in and throughout life), (3) unattached, commissure horizontal (questionably mobile and sessile), (4) unattached, commissure vertical (interarea stabilization and umbonal weighting), (5) functional pedicle (tethered and combined with interarea stabilization). Statistical tests (Median and Mann-Whitney U ) reveal that the unattached, free-lying, questionably mobile genera and the cemented genera among the endemic brachiopods display a significantly greater generic longevity distribution than the unattached, free-lying, stationary and pedunculate genera. Genera cemented throughout their life show a significantly greater longevity distribution than spine-anchored genera. Brachiopod genera which combined interarea stabilization with a pedicle show a significantly greater longevity distribution than genera tethered on a pedicle. Among the cosmopolitan genera, pedunculate and cemented brachiopods display a significantly greater longevity distribution than the unattached, interarea-stabilized genera.