Norman, D. (1994) Prehistoric Life: the Rise of the Vertebrates, London: Boxtree Sheldon, P., Palmer D., Spicer, B. (2001).
Norman, D. (1994) Prehistoric Life: the Rise of the Vertebrates (Viața preistorică: apariția vertebratelor), London: Boxtree Sheldon, P., Palmer D., Spicer, B. (2001).