Darwin had hoped that later fossil discoveries would eventually eliminate what he regarded as the one outstanding anomaly associated with his theory. Walcott’s discovery was not that discovery. Not only did the Burgess Shale fail to reveal the expected ancestral precursors of the known Cambrian animal forms, but it revealed a motley crew of previously unknown animal forms and body plans that now demanded their own lengthy chain of evolutionary precursors, only complicating the task of explaining the Cambrian explosion in Darwinian terms.
