1. Fraser, N.C. Palaeontology 25, 709 (1982); 27, 575 (1984); 29, 165 (1986).
2. Carroll, R.L. Paleontographica A189, 1 (1985).
3. Whiteside, D.I. Phil. Trans. R. Soc. B312, 379 (1986).
4. Darwin, C. On the Origin of Species (Murray, London, 1859).
5. Schopf, T.J.M. A. Rev. Earth planet, Sci. 12, 245 (1984).