1. Janvier, P. Early Vertebrates (Oxford Univ. Press, Oxford, 1996)
2. Turner, S. in Recent Advances in the Origin and Early Radiation of Vertebrates (eds Arratia, G., Wilson, M. V. H. & Cloutier, R.) (Verlag Dr F. Pfeil, Muenchen, in the press)
3. Mader, H. Schuppen und Zähne von Acanthodiern und Elasmobranchiern aus dem Unterdevon Spaniens (Pisces). Göttinger Arb. Geol. Paläont. 28, 1–58 (1986)
4. Maisey, J. G. & Anderson, M. E. A primitive chondrichthyan braincase from the Early Devonian of South Africa. J. Vert. Paleontol. 21, 702–713 (2001)
5. Tucker, R. D. et al. New U-Pb zircon ages and the duration and division of Devonian time. Earth Planet. Sci. Lett. 158, 175–186 (1998)