 In the 1970s and early 1980s the Burgess fossils were largely regarded as evidence that the familiar phyla of animals appeared very rapidly in the Early Cambrian , in what is often called the Cambrian explosion . This view was already known to Charles Darwin , who regarded it as one of the greatest difficulties for the theory of evolution he presented in The Origin of Species in 1859 . However , from the early 1980s the cladistics method of analysing " evolutionary family trees " has persuaded most researchers that many of the Burgess Shale 's " weird wonders " , such as Opabinia and Hallucigenia , were evolutionary " aunts and cousins " of present @-@ day types of animal rather than a rapid proliferation of separate phyla , some of which were short @-@ lived . Nevertheless , there is still debate , sometimes vigorous , about the relationships between some groups of animals . 
