1. Ayala, F.J., Rzhestsky, A., and Ayala, F.J., Origin of the Metazoan Phyla: Molecular Clocks Confirm Paleontological Estimates, Proc. Natl. Acad. Sci. U.S.A., 1998, vol. 95, pp. 606–611.
2. Bengtson, S., Spicules, in Early Cambrian Fossils from South Australia, Bengtson, S., et al., Eds., Mem. Assoc. Australas. Palaeontol., 1990, vol. 9, pp. 24–37.
3. Blair, J.E. and Hedges, S.B., Molecular Phylogeny and Divergence Times of Deuterostome Animals, Mol. Biol. Evol., 2005, vol. 22, no. 11, pp. 2275–2284.
4. Boardman, R.S., Cheetham, A.H., and Blake, D., and Cook, P.L., Bryozoa in Treatise on Invertebrate Paleontology: Part G, Revised, Robinson, R.A., Ed., Boulder and Lawrence: Geol. Soc. Am. and Univ. Kans. Press, 1983, vol. 1, pp. 1–625.
5. Bourlat, S.J., Juliusdottir, T., Lowe, C.J., Freeman, R., Aronowicz, J., Kirschner, M., Lander, E.S., Thorndyke, M., Nakano, H., Kohn, A.B., Heyland, A., Moroz, L.L., Copley, R.R., and Telford, M.J., Deuterostome Phylogeny Reveals Monophyletic Chordates and the New Phylum Xenoturbellida, Nature, 2006, vol. 447, no. 7115, pp. 85–88.