Burgess Shale-Type Faunas and the Origin of Animal Bodyplans: Continuing Confusion?  

If the Burgess Shale and similar Fossil-lagerstätten (notably Chengjiang and Sirius Passet) are famous for anything other than their spectacular preservation, it is the remarkable diversity of forms, amongst which some look “very strange”.  Or so they did, because whilst a number remain in phylogenetic limbo (for example Dinomischus), in many other cases it is now apparent that, despite their bizarre appearances, the various fossil taxa are of unique importance in documenting how various body-plans are assembled.  The importance of this scarcely needs emphasis.  First, even though Darwin spelt out the solution fifty years before Charles Walcott “stumbled” on the Burgess Shale, half the biological community seems to persist in thinking that common ancestors are some vague set of chimaeras, conveniently simplified and carrying a burden of characters they might just need in the next hundred million years or so.  The reality is very different: ancestors are complex and to the first approximation look very different form what some workers think they “ought” to look like and more importantly from their descendant “phyla”.  Second, these transitions are achieved in an unremarkable, microevolutionary fashion: no sudden jumps, no sudden noises.  Third, groups we now identify at the highest taxonomic level were, in the Cambrian, arising from closely related taxa, separated by both trivial genetic and morphological differences.  Here I will outline, in collaboration with my co-workers Jean-Bernard Caron (Toronto), John Peel (Uppsala), and Degan Shu (Xi’an), how we can document some of the key steps in the evolution of the deuterostomes (notably vetulicolians and yunnanozoans), lophotrochozoans (notably halkieriids), and ecdysozoans (notably the palaeoscolecidans).