1. Coates, M. I. & Clack, J. A. Nature 347, 66–69 (1990).
2. Bendix-Almgreen, S. E., Clack, J. A. & Olsen, H. Rapp. Gronlands geol. Unders. 140, 95–102 (1988).
3. Clack, J. A. Nature 342, 425–430 (1989).
4. Miles, R. S. Zool. J. Linn. Soc. 61, 1–328 (1977).
5. Jarvik, E. Basic Structure and Evolution of Vertebrates Vol. I (Academic, London, 1980).