The terebratulides: the supreme brachiopod survivors

Terebratulides are by far the most abundant and diverse group of brachiopods in modern oceans, greatly outnumbering the other articulated rhynchonellide and thecideid brachiopods in terms of both generic and species diversity and in total biomass. Although the small, cemented thecideids have remained a minor brachiopod group from their origin in the Triassic, immense numbers of terebratulides and rhynchonellides inhabited global seas in the Jurassic. Since the Early Cretaceous, however, rhynchonellides have declined in richness and abundance and now form a minor component of terebratulide-dominated faunas, mainly in deep-water habitats. This paper examines some of the distinctive morphological, physiological and ecological characteristics of terebratulides and rhynchonellides in order to explain why terebratulides, of all the articulated brachiopod clades that originated in Palaeozoic seas, should have survived the vicissitudes of environmental and biotic filters such as varying seawater chemistry, changing habitats, oscillating sea temperatures, competition and predation, to become the most successful of all groups of brachiopods.