The lecture notes for the 3rd class – the Cambrian Explosion – can be downloaded here: 2013_LifeThruTime_Lect3
A University of Maryland website discussing ‘The Long Fuse of the Cambrian Explosion’ can be found here.
High-quality artist’s impressions of the weirdos of the Cambrian can be found on National Geographic here.
The fantastic Royal Ontario Museum (ROM) website about the Burgess Shale can be found here.
The equally good online guide to trilobites, by Sam Gon III, can be found here.
A good Wikipedia entry on the problematical early Cambrian fossils called halkieriids is here.
The amazing fossils of Chengjiang, China, are revealed on their UNESCO World Heritage page here.
The 2010 paper by Jean Vannier and colleagues, discussing the possibility that priapulid worms were the makers of the first Cambrian burrows, can be downloaded here: Vannier_etal2010_priapulid_PC