1. Alpert, S. P., 1977, Trace fossils and the basal Cambrian boundary, Geol. J. Spec. Issue 9:1–8.
2. Anderson, D. T., 1973, Embryology and Phylogeny of Annelids and Arthropods, Pergamon Press, Oxford.
3. Arthur, W., 1984, Mechanisms of Morphological Evolution, Wiley, New York.
4. Arthur, W., 1988, A Theory of the Evolution of Development, Wiley, Chichester, England.
5. Barnes, R. S. K. (ed.), 1984, A Synoptic Classification of Living Organisms, Sinauer, Sunderland, Massachusetts.