The life and death of torquirhynchia inconstans (brachiopoda, upper jurassic) in England

Torquirhynchia inconstans, a rhynchonellid brachiopod, shows a curious asymmetric commissure. This is interpreted as an adaptation to life in tidal environments. Type of preservation, growth line, and size frequency analysis indicate that the population analyzed consist of dominantly mature individuals, which by analogy with recent brachiopod populations is a primary feature of the original population, and not due to selective destruction, selective transport, or selective predation of smaller individuals. The possible functions of the asymmetry of Torquirhynchia inconstans are considered, and it is concluded that the brachiopod was adapted to life in tidal environments, a conclusion supported by sedimentological evidence. Asymmetric brachiopods are considered to have developed from colonies of partly asymmetric, variable brachiopods by selection of extreme variants.