ABSTRACT
Terebratulide brachiopods, the most prolific ordinal group of post-Palaeozoic brachiopods, are characterised by the possession of an internal skeleton known as the loop. Terebratulides are potentially important for the inference of morphological evolution, because they are abundant in the fossil record as well as in Recent seas, and their loop morphology exhibited a considerable diversification throughout their evolutionary history. However, it has been difficult to infer evolutionary processes of loop morphology without the risk of circular arguments, because the loop morphology itself has been the prime tool for the assessment of terebratulide relationships (Richardson, 1975). Taxonomic characters independent of loop morphology are needed, such as molecular sequence characteristics.
