Article: A new stem-group chordate from the lower Ordovician of South Wales, and the problem of locomotion in boot-shaped cornutes

The cornute Procothurnocystis owensi gen. et sp. nov.. from the Upper Arenig of South Wales, is reconstructed and described. Within the chordate stem-group, it probably represents a plesion between that of 'Cothurnocystis' fellinensis Ubaghs, 1969, on the anticrownward side, and that of Cothurnocystis elizae Bather, 1913, on the crownward side. On death by burial, the only known specimen of Procothurnocystis owensi seems to have swallowed a mouthful of mud. The locomotory cycles of Procothurnocystis owensi and Cothurnocystis elizae are reconstructed, using hand-powered working models on appropriate substrates of wet clay or wet sand respectively. In its locomotory peculiarities, Procothurnocystis owensi probably represents the more advanced condition and Cothurnocystis elizae the more primitive.